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An alloy is essentially a mixture of two or more elements, the principal component being a metallic element (the ‘parent metal’ or ’solvent’), so that the resultant mixture exhibits metallic properties. A wide variety of mechanical and physical properties may be obtained by alloying, so that alloys, rather than pure metals, are of the greatest importance for engineering.
If the constituent metallic atoms are chemically similar to one another, they will crystallise as a single set of crystals, since all the atoms will behave as if they belonged to the same species. A single-phase solid solution is then said to form, and its microstructure is often indistinguishable from that of a pure metal.
However, there may be a tendency for the elements to crystallise separately to form distinct and different crystals joined at mutual grain boundaries. Such a structure is an example of a phase mixture, which can usually be distinguished from a single-phase solid by metallographic examination.
Note that this could include the formation of an intermetallic compound. These compounds are in themselves of little practical value, since they tend to be hard and brittle, but they can be important as constituents of alloy systems.
1.3 Solid Solutions
Initially when a solid solution is formed the crystal structure is the same as that of the parent metal - the atoms of the solute or alloying element are distributed throughout each crystal, and a range of composition is possible. The solution may be formed in two ways:
(a) In substitutional solid solutions the atoms share a single common array of atomic sites (Fig 4a).
In some systems the parent metal will dissolve any proportion of the solute and retain its original crystal structure. However, in many cases there is a limited solubility and in order to accommodate a larger proportion of the added alloying element a change in the initial crystal structure becomes necessary to form a different solid solution, that is, another phase. In this way two solid solutions may exist together over a range of composition.
(b) In interstitial solid solutions the atoms of the solute element are small enough to fit into the spaces between the parent metal atoms, as illustrated (Fig 4b).
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(a) substitutional
(b) interstitial
Fig 4 The formation of solid solutions
Because of the atom size limitation, interstitial solid solutions are less common than substitutional solutions, although Carbon atoms can dissolve in iron crystals in this way in steel. Similarly Nitrogen can dissolve in steel and this is the basis of the Nitriding surface hardening process. The very small atoms of Hydrogen will dissolve interstitially in ferrous alloys, usually producing brittleness.
1.4 Phase Mixtures
A phase, present in an alloy as a separate entity, can be pure metal, a solid solution or an intermetallic compound. Any mixtures of two or more of these can occur. In binary systems, that is those of two elements, generally not more than two phases can exist together.
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2. EQUILIBRIUM DIAGRAMS
Thermal equilibrium (also known as Phase or Constitutional) diagrams are of great importance in metallurgy for with their aid it is possible to determine exactly the structure of a particular alloy at any given temperature, provided the alloy has been allowed to reach a state of equilibrium. Thus the phases present, their quantities and the chemical composition of each phase can be shown with precision. The diagrams are constructed principally by thermal analysis but also with microscopic studies, the examination of volume changes, X-ray diffraction and other techniques.
Equilibrium can be considered as a state of balance ultimately arrived at by the components at the temperature of the system concerned. However, in some cases such a state would take a very long time to be reached while in others it may never be reached at the temperature in question. For example, if an alloy is rapidly cooled by quenching to room temperature, chemical and physical changes may be suppressed such that they will never take place unless the alloy is reheated to allow them to occur. Very slow cooling must then follow.
2.1 Iron-Carbon Equilibrium Diagram (Fig 5)
Steel may be defined as an alloy of Iron and Carbon (up to about 1.7%C). Here it may be helpful to recall the allotropic nature of iron and that up to 910°C it has a body centred cubic crystalline form known as alpha α Iron, from 910°C-1400°C a face centred cubic structure, gamma γ Iron, reverting to body centred cubic delta δ. Iron above that temperature. These terms are modified in steel to Ferrite, Austenite and δ Ferrite. Other phases in the equilibrium structure are Cementite the inter-metallic compound Fe3C, and, Pearlite a phase mixture known as a Eutectoid consisting in this case of alternate layers of Cementite and Ferrite. Pearlite contains about 0.83%C.
Ferrite and δ Ferrite, the body centred cubic structures dissolve only very small amounts of carbon: less than 0.01% at room temperature. The face centred cubic Austenite however, is capable of dissolving up to nearly 2%C at 1150°C although this structure will change on reaching the Lower Critical Temperature 723°C below which the Eutectoid reaction will be complete. (Fig 6)
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Fig 5 The Iron-Carbon phase diagram
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Fig 6 Part of the Iron-Carbon Thermal-equilibrium diagram
Note that the Lower Critical Temperature 723°C below which all Austenite has been converted to Ferrite and Cementite is commonly known as the A1 temperature. The temperature above which the structure will be wholly Austenite, the Upper Critical Temperature, is known as the A3 temperature. Also the temperature above which the steel reverts to a wholly body centred cubic δ ferrite is known as the A4 temperature.
2.2 Slowly Cooled Structures
The most important reaction in steel is the decomposition of austenite on cooling. Consider the slow cooling of a steel of 0.83%C content (i.e. of the eutectoid composition) (Fig 7a); at 723°C the structure will transform to an eutectoid mixture consisting of alternate lamellae or plates of ferrite and cementite.
A steel of higher carbon content (known as a ‘hyper-eutectoid’ steel) (Fig 7b), 1.20%C, will remain austenitic down to the temperature around, say, 870°C at which the solvus line is crossed, so that Fe3C will start to be precipitated at the austenite grain boundaries.
Continued cooling and precipitation of cementite Fe3C will reduce the carbon content of the austenite until it reaches that of the eutectoid 0.83%C. When the temperature falls to below 723°C, this residual austenite will transform to pearlite, and the final microstructure will be cementite plus pearlite.
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A lower carbon steel (i.e. a ‘hypoeutectoid steel) of 0.4%C (Fig 7c) will begin to transform when the temperature falls below the solvus line by the precipitation of ferrite at the austenite grain boundaries.
Continued cooling and precipitation of ferrite will increase the carbon content of the austenite until it reaches that of the eutectoid 0.83%C. At 723°C this remaining austenite will transform to pearlite resulting in a final structure of ferrite plus pearlite.
2.3 Quenched Structures
The previous microstructures form in plain carbon steels which have been moderately slowly cooled (e.g. by cooling in air) from temperatures within the austenitic phase field, say from 50°C above the lower boundary line CED. This is called a ‘normalising’ heat treatment, but medium and high-carbon steels are very commonly subjected to more complex treatments in order fully to exploit their properties. These treatments involve, first, heating the alloy into the austenite phase field, as before, but then quenching it in water or brine which suppresses diffusion and thus the formation of ferrite and cementite. Under these conditions the austenite transforms by a process not involving diffusion into a metastable distorted form of body-centred iron known as ‘Martensite’ (Fig 7d). This process is extremely rapid and the transformation may be completed in a few microseconds.

All the carbon originally dissolved in the Austenite at high temperature remains after quenching in interstitial solution in the Martensite crystals. This has the effect of distorting the lattice from cubic to tetragonal symmetry. This lattice distortion by the dissolved carbon has the effect of hardening the structure and the resulting steels will not only be hard but brittle, for which there is little practical application. A second heat treatment called tempering is therefore required and this will reduce hardness and brittleness. If Martensitic steel is reheated to the temperature range 200-600°C (below the Austenite forming temperature) it rapidly decomposes to form body centred cubic ferrite and particles of Cementite.
This structure is on an extremely fine scale, the size of the carbide particles being dependent on the time and temperature of the treatment. The higher the temperature and the longer the time, the softer and less brittle the product.

HTML clipboardAngle Valve: A valve design in which one port is co-linear with the valve stem or actuator, and the other port is at a right angle to the valve stem. (See also Globe Valve.) Bellows Seal Bonnet: A bonnet that uses a bellows for sealing against leakage around the closure member stem (figure 1–6). Bonnet: The portion of the valve that contains the packing box and stem seal and can guide the stem. It provides the principal opening to the body cavity for assembly of internal parts or it can be an integral part of the valve body. It can also provide for the attachment of the actuator to the valve body.

Typical bonnets are bolted, threaded, welded, pressureseals, or integral with the body. (This term is often used in referring to the bonnet and its included packing parts. More properly, this group of component parts should be called the bonnet assembly.) Bonnet Assembly: (Commonly Bonnet, more properly Bonnet Assembly): An assembly including the part through which a valve stem moves and a means for sealing against leakage along the stem. It usually provides a means for mounting the actuator and loading the packing assembly. Bottom Flange: A part that closes a valve body opening opposite the bonnet opening. It can include a guide bushing and/or serve to allow reversal of the valve action. Bushing: A device that supports and/ or guides moving parts such as valve stems.

Cage: A part of a valve trim that surrounds the closure member and can provide flow characterization and/or a seating surface. It also provides stability, guiding, balance, and alignment, and facilitates assembly of other parts of the valve trim. The walls of the cage contain openings that usually determine the flow characteristic of Chapter 1. Introduction to Control Valves 10 Figure 1-8. Characterized Cages for Globe-Style Valve Bodies W0958/IL W0959/IL W0957/IL   
 
 the control valve. Various cage styles are shown in figure 1-8. Closure Member: The movable part of the valve that is positioned in the flow path to modify the rate of flow through the valve. Closure Member Guide: That portion of a closure member that aligns its movement in either a cage, seat ring, bonnet, bottom flange, or any two of these. Cylinder: The chamber of a piston actuator in which the piston moves (figure 1-7). Cylinder Closure Seal: The sealing element at the connection of the piston actuator cylinder to the yoke. Diaphragm: A flexible, pressure responsive element that transmits force to the diaphragm plate and actuator stem. Diaphragm Actuator: A fluid powered device in which the fluid acts upon a flexible component, the diaphragm. Diaphragm Case: A housing, consisting of top and bottom section, used for supporting a diaphragm and establishing one or two pressure chambers. Diaphragm Plate: A plate concentric with the diaphragm for transmitting force to the actuator stem. Direct Actuator: A diaphragm actuator in which the actuator stem extends with increasing diaphragm pressure. Extension Bonnet: A bonnet with greater dimension between the packing box and bonnet flange for hot or cold service. Globe Valve: A valve with a linear motion closure member, one or more ports, and a body distinguished by a globular shaped cavity around the port region. Globe valves can be further classified as: two-way single-ported; two-way double-ported (figure 1-9); angle-style (figure 1-10); three-way (figure 1-11); unbalanced cage-guided (figure 1-3); and balance cage-guided (figure 1-12). Lower Valve Body: A half housing for internal valve parts having one flow connection. The seat ring is normally clamped between the upper valve body and the lower valve body in split valve constructions.

Offset Valve: A valve construction having inlet and outlet line connections on different planes but 180 degrees opposite each other. Packing Box (Assembly): The part of the bonnet assembly used to seal against leakage around the closure Chapter 1. Introduction to Control Valves 11 Figure 1-9. Reverse Double-Ported Globe-Style Valve Body W0467/IL Figure 1-10. Flanged Angle-Style Control Valve Body W0971/IL member stem. Included in the complete packing box assembly are various combinations of some or all of the following component parts: packing, packing follower, packing nut, lantern ring, packing spring, packing flange, packing flange studs or bolts, packing flange nuts, packing ring, packing wiper ring, felt wiper ring, belleville springs, anti-extrusion ring. Individual Figure 1-11. Three-Way Valve with Balanced Valve Plug W0665/IL Figure 1-12. Valve Body with Cage-Style Trim, Balanced Valve Plug, and Soft Seat W0992/IL packing parts are shown in figure 1-13. Piston: A movable pressure responsive element that transmits force to the piston actuator stem (figure 1-7). Piston Type Actuator: A fluid powered device in which the fluid acts upon a movable piston to provide motion to the actuator stem. Piston type actuators (figure 1-7) are classified as either double-acting, so that full power Chapter 1. Introduction to Control Valves 12 Figure 1-13. Comprehensive Packing Material Arrangements for Globe-Style Valve Bodies B2565 / IL LOCATION OF SACRIFICIAL ZINC WASHER, IF USED. 
  

 14A1849-E 1 12A7837-A 
  
 13A9775-E can be developed in either direction, or as spring-fail so that upon loss of supply power, the actuator moves the valve in the required direction of travel. Plug: A term frequently used to refer to the closure member. Port: The flow control orifice of a control valve. Retaining Ring: A split ring that is used to retain a separable flange on a valve body. Reverse Actuator: A diaphragm actuator in which the actuator stem retracts with increasing diaphragm pressure. Reverse actuators have a seal bushing (figure 1-4) installed in the upper end of the yoke to prevent leakage of the diaphragm pressure along the actuator stem. Rubber Boot: A protective device to prevent entrance of damaging foreign material into the piston actuator seal bushing. Seal Bushing: Top and bottom bushings that provide a means of sealing the piston actuator cylinder against leakage. Synthetic rubber O-rings are used in the bushings to seal the cylinder, the actuator stem, and the actuator stem extension (figure 1-7). Seat: The area of contact between the closure member and its mating surface that establishes valve shut-off. Seat Load: The net contact force between the closure member and seat with stated static conditions. In practice, the selection of an actuator for a given control valve will be based on how much force is required to overcome static, stem, and dynamic unbalance with an allowance made for seat load. Seat Ring: A part of the valve body assembly that provides a seating surface for the closure member and can provide part of the flow control orifice. Separable Flange: A flange that fits over a valve body flow connection. It is generally held in place by means of a retaining ring. Spring Adjustor: A fitting, usually threaded on the actuator stem or into

Chapter 1. Introduction to Control Valves 13 the yoke, to adjust the spring compression. Spring Seat: A plate to hold the spring in position and to provide a flat surface for the spring adjustor to contact. Static Unbalance: The net force produced on the valve stem by the fluid pressure acting on the closure member and stem with the fluid at rest and with stated pressure conditions. Stem Connector: The device that connects the actuator stem to the valve stem. Trim: The internal components of a valve that modulate the flow of the controlled fluid. In a globe valve body, trim would typically include closure member, seat ring, cage, stem, and stem pin. Trim, Soft-Seated: Valve trim with an elastomeric, plastic or other readily deformable material used either in the closure component or seat ring to provide tight shutoff with minimal actuator forces. Upper Valve Body: A half housing for internal valve parts and having one flow connection. It usually includes a means for sealing against leakage along the stem and provides a means for mounting the actuator on the split valve body. Valve Body: The main pressure boundary of the valve that also provides the pipe connecting ends, the fluid flow passageway, and supports the seating surfaces and the valve closure member. Among the most common valve body constructions are: a) single-ported valve bodies having one port and one valve plug; b) double-ported valve bodies having two ports and one valve plug; c) twoway valve bodies having two flow connections, one inlet and one outlet; d) three-way valve bodies having three flow connections, two of which can be inlets with one outlet (for converging or mixing flows), or one inlet and two outlets (for diverging or diverting flows). The term valve body, or even just body, frequently is used in referring to the valve body together with its bonnet assembly and included trim parts. More properly, this group of components should be called the valve body assembly. Valve Body Assembly (Commonly Valve Body or Valve, more properly Valve Body Assembly): An assembly of a valve, bonnet assembly, bottom flange (if used), and trim elements. The trim includes the closure member, which opens, closes, or partially obstructs one or more ports. Valve Plug: A term frequently interchanged with plug in reference to the closure member. Valve Stem: In a linear motion valve, the part that connects the actuator stem with the closure member. Yoke: The structure that rigidly connects the actuator power unit to the valve.

HTML clipboardLinear Characteristic*: An inherent flow characteristic that can be repreChapter 1. Introduction to Control Valves 5 sented by a straight line on a rectangular plot of flow coefficient (Cv) versus rated travel. Therefore equal increments of travel provide equal increments of flow coefficient, Cv (figure 1-2). Loop: (See Closed Loop.) Loop Gain: The combined gain of all the components in the loop when viewed in series around the loop. Sometimes referred to as open-loop gain. It must be clearly specified whether referring to the static loop gain or the dynamic loop gain at some frequency.

Manual Control: (See Open Loop.) Open Loop: The condition where the interconnection of process control components is interrupted such that information from the process variable is no longer fed back to the controller set point so that corrections to the process variable are no longer provided. This is typically accomplished by placing the controller in the manual operating position. Packing: A part of the valve assembly used to seal against leakage around the valve disk or stem. Positioner*: A position controller (servomechanism) that is mechanically connected to a moving part of a final control element or its actuator and that automatically adjusts its output to the actuator to maintain a desired position in proportion to the input signal. Process: All the combined elements in the control loop, except the controller. The process typically includes the control valve assembly, the pressure vessel or heat exchanger that is being controlled, as well as sensors, pumps, and transmitters.

Process Gain: The ratio of the change in the controlled process variable to a corresponding change in the output of the controller. Process Variability: A precise statistical measure of how tightly the process is being controlled about the set point. Process variability is defined in percent as typically (2s/m), where m is the set point or mean value of the measured process variable and s is the standard deviation of the process variable. Quick Opening Characteristic*:

An inherent flow characteristic in which a maximum flow coefficient is achieved with minimal closure member travel (figure 1-2). Relay: A device that acts as a power amplifier. It takes an electrical, pneumatic, or mechanical input signal and produces an output of a large volume flow of air or hydraulic fluid to the actuator. The relay can be an internal component of the positioner or a separate valve accessory. Resolution: The minimum possible change in input required to produce a detectable change in the output when no reversal of the input takes place.

Resolution is typically expressed as a percent of the input span. Response Time: Usually measured by a parameter that includes both dead time and time constant. (See T63, Dead Time, and Time Constant.) When applied to the valve, it includes the entire valve assembly. Second-Order: A term that refers to the dynamic relationship between the input and output of a device. A second- order system or device is one that has two energy storage devices that can transfer kinetic and potential energy back and forth between themselves, thus introducing the possibility of oscillatory behavior and overshoot. Sensor: A device that senses the value of the process variable and provides a corresponding output signal to a transmitter. The sensor can be an integral part of the transmitter, or it may be a separate component. Chapter 1. Introduction to Control Valves 6 Set Point: A reference value representing the desired value of the process variable being controlled. Shaft

Wind-Up: A phenomenon where one end of a valve shaft turns and the other does not. This typically occurs in rotary style valves where the actuator is connected to the valve closure member by a relatively long shaft. While seal friction in the valve holds one end of the shaft in place, rotation of the shaft at the actuator end is absorbed by twisting of the shaft until the actuator input transmits enough force to overcome the friction. Sizing (Valve): A systematic procedure designed to ensure the correct valve capacity for a set of specified process conditions. Stiction: (See Friction.) T63 (Tee-63): A measure of device response. It is measured by applying a small (usually 1-5%) step input to the system. T63 is measured from the time the step input is initiated to the time when the system output reaches 63% of the final steady-state value. It is the combined total of the system Dead Time (Td) and the system Time Constant (t). (See Dead Time and Time Constant.) Time Constant: A time parameter that normally applies to a first-order element. It is the time interval measured from the first detectable response of the system to a small (usually 0.25% - 5%) step input until the system output reaches 63% of its final steady-state value. (See T63.) When applied to an open-loop process, the time constant is usually designated as
(Tau). When applied to a closed-loop system, the time constant is usually designated as λ (Lambda). Transmitter: A device that senses the value of the process variable and transmits a corresponding output signal to the controller for comparison with the set point. Travel*: The movement of the closure member from the closed position to an intermediate or rated full open position. Travel Indicator: A pointer and scale used to externally show the position of the closure member typically with units of opening percent of travel or degrees of rotation. Trim*: The internal components of a valve that modulate the flow of the controlled fluid.

Valve: (See Control Valve Assembly.) Volume Booster: A stand-alone relay is often referred to as a volume booster or simply booster because it boosts, or amplifies, the volume of air supplied to the actuator. (See Relay.) Sliding-Stem Control Valve Terminology The following terminology applies to the physical and operating characteristics of standard sliding-stem control valves with diaphragm or piston actuators. Some of the terms, particularly those pertaining to actuators, are also appropriate for rotary-shaft control valves. Many of the definitions presented are in accordance with ISA S75.05,

Control Valve Terminology, although other popular terms are also included. Additional explanation is provided for some of the more complex terms. Component part names are called out on accompanying figures 1-3 through 1-6. Separate sections follow that define specific rotaryshaft control valve terminology, control valve functions and characteristics terminology, and other process control terminology. Actuator Spring: A spring, or group of springs, enclosed in the yoke or actuator casing that moves the actuator stem in a direction opposite to that created by diaphragm pressure.

HTML clipboardThe controller output (CO) is the input to the valve assembly and the process variable (PV) is the output as shown in figure 1-1. When the term Dead Band is used, it is essential that both the input and output variables are identified, and that any tests to measure dead band be under fully loaded conditions. Dead band is typically expressed as a percent of the input span. Dead Time: The time interval (Td) in which no response of the system is detected following a small (usually 0.25% - 5%) step input.

It is measured from the time the step input is initiated to the first detectable response of the system being tested. Dead Time can apply to a valve assembly or to the entire process. (See T63.) Disk: A valve trim element used to modulate the flow rate with either linear or rotary motion. Can also be referred to as a valve plug or closure member.

Equal Percentage Characteristic*: An inherent flow characteristic that, for equal increments of rated travel, will ideally give equal percentage changes of the flow coefficient (Cv) (figure 1-2). Final Control Element: The device that implements the control strategy determined by the output of the controller. While the final control element can be a damper, a variable speed drive pump, or an on-off switching device, the most common final control element in the process control industries is the control valve assembly. The control valve manipulates a flowing fluid, such as gasses, steam, water, or chemical compounds, to compensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point. First-Order: A term that refers to the dynamic relationship between the input and output of a device. A first-order system or device is one that has only one energy storage device and whose dynamic transient relationship between the input and output is characterized by an exponential behavior. Friction: A force that tends to oppose the relative motion between two surfaces that are in contact with each other. The friction force is a function of the normal force holding these two surfaces together and the characteristic nature of the two surfaces. Friction has two components: static friction and dynamic friction. Static friction is the force that must be overcome before there is any relative motion between the two surfaces. Once relative movement has begun, dynamic friction is the force that must be overcome to maintain the relative motion. Running or sliding friction are colloquial terms that are sometimes used to describe dynamic friction. Stick/slip or “stiction” are colloquial terms that are sometimes used to describe static friction. Static friction is one of the major causes of dead band in a valve assembly. Gain: An all-purpose term that can be used in many situations. In its most general sense, gain is the ratio of the magnitude of the output change of a given system or device to the magnitude of the input change that caused the output change. Gain has two components: static gain and dynamic gain. Static gain is the gain relationship between the input and output and is an indicator of the ease with which the input can initiate a change in the Chapter 1. Introduction to Control Valves 4 Figure 1-2. Inherent Valve Characteristics A3449/IL output when the system or device is in a steady-state condition. Sensitivity is sometimes used to mean static gain. Dynamic gain is the gain relationship between the input and output when the system is in a state of movement or flux. Dynamic gain is a function of frequency or rate of change of the input. Hysteresis*:

The maximum difference in output value for any single input value during a calibration cycle, excluding errors due to dead band. Inherent Characteristic*: The relationship between the flow coefficient and the closure member (disk) travel as it is moved from the closed position to rated travel with constant pressure drop across the valve. Typically these characteristics are plotted on a curve where the horizontal axis is labeled in percent travel and the vertical axis is labeled as percent flow (or Cv) (figure 1-2). Because valve flow is a function of both the valve travel and the pressure drop across the valve, conducting flow characteristic tests at a constant pressure drop provides a systematic way of comparing one valve characteristic design to another. Typical valve characteristics conducted in this manner are named Linear, Equal-Percentage, and Quick Opening (figure 1-2). Inherent Valve Gain: The magnitude ratio of the change in flow through the valve to the change in valve travel under conditions of constant pressure drop. Inherent valve gain is an inherent function of the valve design. It is equal to the slope of the inherent characteristic curve at any travel point and is a function of valve travel. Installed Characteristic*: The relationship between the flow rate and the closure member (disk) travel as it is moved from the closed position to rated travel as the pressure drop across the valve is influenced by the varying process conditions. (See Valve Type and Characterization in Chapter 2 for more details on how the installed characteristic is determined.) Installed Valve Gain: The magnitude ratio of the change in flow through the valve to the change in valve travel under actual process conditions. Installed valve gain is the valve gain relationship that occurs when the valve is installed in a specific system and the pressure drop is allowed to change naturally according to the dictates of the overall system. The installed valve gain is equal to the slope of the installed characteristic curve, and is a function of valve travel.

(See Valve Type and Characterization in Chapter 2 for more details on how the installed gain is determined.) I/P: Shorthand for current-to-pressure (I-to-P). Typically applied to input transducer modules. Linearity*: The closeness to which a curve relating to two variables approximates a straight line. (Linearity also means that the same straight line will apply for both upscale and downscale directions. Thus, dead band as defined above, would typically be considered a non-linearity.)

HTML clipboardWhat Is A Control Valve?

Process plants consist of hundreds, or even thousands, of control loops all networked together to produce a product to be offered for sale. Each of these control loops is designed to keep some important process variable such as pressure, flow, level, temperature, etc. within a required operating range to ensure the quality of the end product. Each of these loops receives and internally creates disturbances that detrimentally affect the process variable, and interaction from other loops in the network provides disturbances that influence the process variable.

To reduce the effect of these load disturbances, sensors and transmitters collect information about the process variable and its relationship to some desired set point. A controller then processes this information and decides what must be done to get the process variable back to where it should be after a load disturbance occurs. When all the measuring, comparing, and calculating are done, some type of final control element must implement the strategy selected by the controller. The most common final control element in the process control industries is the control valve.

The control valve manipulates a flowing fluid, such as gas, steam, water, or chemical compounds, to compensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point. Many people who talk about control valves or valves are really referring to a control valve assembly. The control valve assembly typically consists of the valve body, the internal trim parts, an actuator to provide the motive power to operate the valve, and a variety Chapter 1. Introduction to Control Valves 2 of additional valve accessories, which can include positioners, transducers, supply pressure regulators, manual operators, snubbers, or limit switches. Other chapters of this handbook supply more detail about each of these control valve assembly components. Whether it is called a valve, control valve or a control valve assembly, is not as important as recognizing that the control valve is a critical part of the control loop. It is not accurate to say that the control valve is the most important part of the loop. It is useful to think of a control loop as an instrumentation chain. Like any other chain, the whole chain is only as good as its weakest link. It is important to ensure that the control valve is not the weakest link. Following are definitions for process control, sliding-stem control valve, rotary-shaft control valve, and other control valve functions and characteristics terminology.

NOTE: Definitions with an asterisk (*) are from the ISA Control Valve Terminology draft standard S75.05 dated October, 1996, used with permission. Process Control Terminology Accessory: A device that is mounted on the actuator to complement the actuator’s function and make it a complete operating unit. Examples include positioners, supply pressure regulators, solenoids, and limit switches. Actuator*: A pneumatic, hydraulic, or electrically powered device that supplies force and motion to open or close a valve. Actuator Assembly: An actuator, including all the pertinent accessories that make it a complete operating unit. Backlash: The general name given to a form of dead band that results from a temporary discontinuity between the input and output of a device when the input of the device changes direction. Slack, or looseness of a mechanical connection is a typical example. Capacity* (Valve): The rate of flow through a valve under stated conditions.

Closed Loop: The interconnection of process control components such that information regarding the process variable is continuously fed back to the controller set point to provide continuous, automatic corrections to the process variable. Controller: A device that operates automatically by use of some established algorithm to regulate a controlled variable. The controller input receives information about the status of the process variable and then provides an appropriate output signal to the final control element. Control Loop: (See Closed Loop.) Control Range: The range of valve travel over which a control valve can maintain the installed valve gain between the normalized values of 0.5 and 2.0. Control Valve: (See Control Valve Assembly.) Control Valve Assembly: Includes all components normally mounted on the valve: the valve body assembly, actuator, positioner, air sets, transducers, limit switches, etc. Dead Band: The range through which an input signal can be varied, upon reversal of direction, without initiating an observable change in the output signal. Dead band is the name given to a general phenomenon that can apply to any device. For the valve

Once considered the theoretical concept of academics, rarely applied in practice, life cycle cost analysis is fast becoming the accepted method for the evaluation of both capital projects and items of replacement plant. Indeed to assist pump users in the evaluation of whole life costs, the Confederation of Pump Manufacturers has in 1999 issued a specification (LLC) for establishing and reducing Life-cycle costs.
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The developed world has become acutely aware of the effect of its waste and the introduction of levies on CO2 emissions, now directly taxes the inefficient users of energy. Globalisation is squeezing maintenance budgets and demanding an increased mean time between major service outages.
Initial capital cost is, in most instances, a fraction of the whole life cost of a typical pumping installation. Energy consumption, unplanned downtime, maintenance and replacement parts can easily equate to in excess of 95% of the total life-cycle cost.
The increasing recognition amongst pump users that post installation costs clearly outweigh capital costs and are therefore the only true economic indicator applicable to capital purchases, prompted SPP Pumps Ltd to set up a combined Marketing & Engineering team to develop a range of low life-cycle cost utilities pumps.

Life-cycle Cost Analysis
What are the real costs associated with procuring, operating and maintaining water utility pumping plant? What are the largest, most variable or most invisible costs? Life-cycle cost can be broken-down for analysis purposes into a number of key components.
§ Initial Capital Cost
§ Operating/Energy Costs
§ Replacement/Wear Part Costs
§ Maintenance & Repair Costs
§ Disposal Costs

Initial Capital Cost
Capital cost is the most visible cost and has historically been the primary selection criterion for most items of capital equipment. Pump users are now becoming increasingly aware of post installation costs and their impact on the total cost of ownership. Lowest capital cost purchases rarely prove economic in the longer term and given that the initial capital cost of a centrifugal pump, inclusive of installation, typically equates to between 5%-20% of whole life cost, placing more emphasis on post installation cost will clearly prove much more economic.

Operating/Energy Costs
Energy costs can easily equate to as much as 90% of the whole life cost of a pumping installation, dependant on installed power and equipment utilisation. Analysis of operating costs, in terms of energy consumption, is relatively straightforward, given that pump utilisation and demand profiles are understood and predictable. The wire to water efficiency of existing or proposed installations can be compared and the results projected over the estimated lifetime of the installation. This should be a fundamental component of any tender assessment process or existing asset review procedure. The attached chart clearly depicts the cost of inefficiency, whilst providing visibility into the post installation savings associated with installing the most efficient equipment for a given duty.
Less visible however, is an installations capacity to operate at or near optimum efficiency throughout its operational life. A degree of degradation in hydraulic performance is inevitable with time. This degradation in performance is primarily a result of wear and erosion of internal clearances. Wear rings limit fluid re-circulation between the high and low-pressure areas within a centrifugal pump. A combination of erosion from high velocity fluid passing between the wear ring surfaces and mechanical wear, resultant from shaft deflection widens the clearances allowing an increase in internal re-circulation. Significantly, highlighting the importance of optimum pump selection, this process will be accelerated if the pump operates at a duty point less than 70% or more than 115% of best efficiency flow. The resultant loss of performances usually leads to the pump running for longer periods to deliver a given quantity of fluid. Erosion of hydraulic profiles and increases in the relative roughness of surfaces in contact with the pumped fluid, will also significantly impact on pump performance.

Replacement/Wear Part Costs
The replacement of major components within a pump, whether as a result of wear, erosion or following a component failure is often a very significant contributor to whole life costs. A replacement rotating assembly will typically equate to 70% of the costs of a replacement pump. It is not uncommon for all components forming the rotating assembly to require replacement within the lifetime of a installation. The selection of a conservatively engineered pump, manufactured from high-grade materials should negate this, substantially reducing maintenance costs and increasing the mean time between failure and major service outages.

Maintenance & Repair Costs
The cost of regular monitoring and preventative maintenance is a necessary component of an installations whole life cost and historical evidence shows that regular maintenance is a lower cost option than unplanned emergency repairs. When calculating the cost of maintenance, installation downtime and resultant loss of productivity should be considered. Savings associated with increased mean time between failure and service outages will offset any higher initial capital costs incurred when installing a well-engineered pump, designed for ease of maintenance.
A well-engineered installation should be so designed as to offer good bearing and seal life and facilitate all but a major overhaul insitu, without recourse to disturb either pipework or prime movers.

Features
Having identified the key constituent parts of whole life cost, what key features would be required of a low life-cycle cost centrifugal pump? The majority of pumps employed on utility type applications fall into the category of either, Horizontal Split Casing, Vertical Suspended Bowl or End Suction Pumps. Only the latter are regularly manufactured to recognised international standards e.g. ISO 5199. The requirement for low life-cycle cost pumps was identified as being mainly for branch sizes 150mm and above and not really applicable to the majority of End Suction Pump applications. The following key areas were identified following discussions between pump users and designers.

Mechanical Design
A significant change has taken place over the last decade in that the switch from soft packed glands to mechanical seals for shaft sealing on utility applications is near universal. The benefits of this change however have not been fully realised, as mechanical seal life is generally proportional to certain key aspects of pump performance, not least shaft deflection, vibration levels and seal chamber design. The vast majority of utility pumps available today have their design roots in the packed gland era. In many instances this is leading to premature bearing and seal failures, as many pump shafts are quite simply too flexible without the support of numerous packing rings and neck bushes.
This is arguably the most significant factor, influencing the mean time between failures of utility pumps. Mechanical seals and bearings are intolerant of shaft deflection and residual unbalance. Therefore I suggest that a pump designed for low life-cycle cost would have a shorter span between bearings and an increased shaft diameter when compared to a similar pump designed in the packed gland era. Specifically shafts should be so designed, as to limit shaft deflection at the limits of the operating range of say, 50% - 115% of best efficiency flow, to a maximum of 0.05mm at the seal faces. Bearings likewise should be designed to provide a minimum L10 life of 50,000 hours at these limits.

Hydraulic Design
With the aid of 3-Dimensional Computational Fluid Dynamics, pump manufacturers are now able to produce hydraulic designs that achieve the theoretical maximum efficiency for a given specific speed or impeller geometry. The challenge is then to consistently replicate these designs in material form. High quality manufacturing techniques and procedures are therefore essential, particularly as pump casings and impellers (the most dimensionally critical components of any centrifugal pump) tend to be produced as castings. Only foundry techniques that ensure a high standard of dimensional accuracy and surface finish should be employed in low life-cycle cost pump production.

Efficiency Degradation
The maximum benefit of installing an energy efficient machine will only be realised if performance levels can be maintained for long periods of time between overhauls. Performance degradation is inevitable, however a combination of good hydraulic and mechanical design can have a positive impact in this area and prolong optimum efficiency for much longer periods of time.
Important hydraulic designs consi-derations are:
§ Maintenance of optimum clearances between the impeller outside diameter and the volute cut-water, which will avoid vane pass cavitation.
§ Optimisation of impeller geometry with satisfactory suction specific speed values, this will limit internal re-circulation and facilitate a wide band of operation (30%-115% of best efficiency flow).
§ Apply internal hydrophobic coating (low electronic affinity) in order to reduce the relative surface roughness value of the pump casing; Thus maintaining the relative surface roughness values at a more constant level, unlike that of a bare metal casing, which will oxidise once put into service immediately impacting on hydraulic performance.
Mechanical design considerations:
§ Minimisation of shaft deflection will ensure no contact between impeller eye ring and sealing/wear rings surfaces, thus maintaining as new clearances for longer periods.
§ Often overlooked but highly important is wear ring design. A labyrinth profile will help to provide a staged pressure drop across the wear ring, rather than simply allowing high velocity fluid to flow across wear ring faces rapidly eroding internal clearances.
§ High-grade materials of construction for the pump impeller with good erosion/corrosion properties will ensure that the relative roughness of hydraulic surfaces remain reasonably smooth throughout.

Packaging the Pumpset
When packaging a low life-cycle cost pump with a suitable prime mover, it is important to ensure that the same fundamental design principles be applied to the prime mover, baseplate/mounting assembly.
The benefits of a superior hydraulic design and first class component quality can easily be forfeited by coupling the highly efficient pump to a lower efficiency driver. Likewise bearing and seal design lives will not be realised if the pump and driver are connected via a flexible and inadequate baseplate or mounting frame.
The mounting arrangement as well as being rigid should facilitate a high degree of insitu maintenance. Mechanical seals and bearings should be accessible without recourse to disturb either driver alignment of connecting pipework. This dictates the use of spacer type couplings, if drive end bearings and seals are to be maintainable insitu.

Conclusion/Design Brief
Following the marketing & design review it was decided to develop a range of low life-cycle pumps, for water utility applications, based on the following brief:
A low life-cycle cost centrifugal pump will have hydraulic efficiency close to the theoretical maximum, thus minimising energy costs, identified as the largest single component cost.
In order to meet the demands of the 21st century utility application the pump should show stable characteristics associated with optimum suction specific speed, thus being able to operate reliably and efficiently across a wide range of flow conditions.
Shaft deflection should be kept to the absolute minimum in order to reduce vibration and maximise bearing and seal life. Specifically shaft deflection at the seal face with mechanically sealed pumps should not exceed seal manufacturers recommendations. This calculation should be carried out across all potential operating conditions. The pumps should firstly be designed for mechanical seals, which should be fitted directly onto the pump shaft, facilitating larger shaft diameters and reduced bearing spans..
Pumps should be so designed and pumpsets so configured that mechanical seals and bearings can be removed and replaced insitu without recourse to disturb either pipework or driver alignment. This will substantially reduce maintenance costs.
High-grade materials of construction should be utilised to maximise component life.
Pumps must not only be energy efficient as new, but must maintain a high efficiency for longer period between major overhauls.

SPP’s Lowest Life-cycle Cost Series
During October 2004 SPP Pumps Ltd successfully launched their Lowest Life-cycle Cost Series pumps. The range incorporates all of the key features identified by our business partners and design engineers.

Hydraulic Design
The above test curve depicts the hydraulic performance of a 200 mm discharge Horizontal Split Casing, radial vane impeller, from the Lowest Life-cycle Cost Series range. Values of NS 1,191 and NSS 7,886, in imperial units. Note that high efficiency is achieved from 50% of best efficiency flow, peaking at 90% actual efficiency.

Mechanical Design
Vertical Direct Mounted Low Life Cost Axial Split casing Pump
The above section drawing depicts a packaged axial split casing pump. Firstly note the maintenance features of the pump; the motor mounting stool is extended to accommodate a spacer type coupling, sized to facilitate removal of the drive end seal and cartridge mounted mechanical seal insitu, also note that a product lubricated bearing is fitted at the none drive end. An antifriction bearing would be susceptible should the installation flood or the lower seal fail. A double row thrust bearing assembly is chosen for the drive end.
The short bearing span and generous shaft diameter are clearly evident. In order to replicate good hydraulic design in material form, world class manufacturing methodology is required. Note the internal surface finish on the above double suction impeller. SPP Low Life-cycle cost pumps achieve predicated performance levels with very little variation or need to hand finish components. Austenitic stainless steel is the optimum impeller material combining excellent corrosion and mechanical properties with good castability.
Standard materials of construction for low life-cycle cost utility pumps are:-
§ Casing- Cast Iron (option coated)
§ Impeller – Austenitic Stainless Steel
§ Shaft – Chrome Steel
§ Wear Rings – Grade SG Iron

Baseplates
Low levels of vibration and accurate alignment of pump and driver cannot be maintained without a substantial baseplate. A low life-cycle cost baseplate should be rigid, easily grouted in and incorporate motor alignment screws and machined mounting pads to assist with site alignment.

Vertical Suspended Bowl Pumps
Major savings in civil engineering costs can be achieved by suspending a vertical shaft driven or submersible pump directly into a wet sump, as opposed to constructing a wet sump with accompanying flood resistant dry well.
This has resulted in a growth in vertical turbine and submersible pump sales. The majority of these pumps supplied for utilities applications however are not maintainable in-situ and are proving very expensive to repair. Submersible pumps are prone to electrical failure, owing to ingress of water and tend to have limited bearing life. Motor efficiencies also tend to be low when compared to TEFC energy efficient machines.
The majority of vertical suspended bowl pumps require removal from site into a workshop environment for minor service/replacement of bearings and mechanical seals. Major overhaul can often result in a need to replace line shafting and connecting coupling which are screwed together.
When applying the same low life-cycle cost philosophy to suspended bowl pumps, major consideration was given to mechanical seal replacement in-situ and as such a bespoke spacer coupling was developed, capable of transmitting the total thrust generated by the bowl assemblies, through to the headpiece thrust bearing. This facilitates mechanical seal replacement in-situ, without recourse to disturb either the drive motor or thrust bearing assembly.
It was decided to connect all intermediate shafting by keyed couplings thus facilitating disassembly without risk of damaging these expensive component parts.
Shaft lengths were limited and diameters set to ensure all pumps operate well below the first critical speed. An important consideration given the growing use of variable speed drives.

Summary
This short paper serves to demonstrate the concept employed by SPP in the development of a genuine range of low life-cycle cost pumps.
A thorough understanding of the intended application, operation and maintenance of pumping plant is a fundamental requirement when considering such a project. This could not have been achieved without the input of pump users and designers alike. <<

The Pneutronics Division of Parker Hannifin
announces the release of its new Low Energy Solenoid Valve, the TenX® Le. This
electro-magnetic poppet valve offers high performance in a lightweight 10mm design.

Providing up to 22lpm of flow through a 0.060in orifice, this 2/3-way
normally closed, normally open or 3-way distributor valve operates at up to 30psi with a fast response time (to 5 msec full cycle) and high reliability (rated for 20 million cycles without any performance degradation). The TenX® Le incorporates efficient pulse width modulation (PWM) circuit technology, which consumes an insignificant amount of power and generates minimal heat, making it an ideal fit for portable medical and analytical devices.

“We designed the TenX® Le to meet the needs of customers who require solenoid control and are sensitive to the size and power constraints on their systems.” says Dan Bantz, Product Manager at Pneutronics. “This integrated valve and electronics solution offers a pulse and hold circuit which drastically reduces energy requirements and fits this into a compact 10mm package - essential requirements for portable equipment”

The miniaturized pulse and hold circuit is virtually invisible since it is
perfectly integrated into the 10mm valve package. The circuit function is also
transparent to the application and does not require extra connectivity. The TenX® Le can be used as a stand alone valve with tube connections or in multi-station manifold mount applications.

More information is available at www.parker.com/pneutronics/tenX.

About Parker

With annual sales exceeding $12 billion, Parker Hannifin is the world’s
leading diversified manufacturer of motion and control technologies and systems,
providing precision-engineered solutions for a wide variety of commercial, mobile,
industrial and aerospace markets. The company employs more than 61,000 people in 48
countries around the world. Parker has increased its annual dividends paid to shareholders for 52 consecutive years, among the top five longest-running dividend-increase records in the S&P 500 index.

Where process applications require control valves which are able to withstand the effects of highly corrosive media Badger RC250 barstock valves are the ideal choice.

The Badger range of valves is available in the UK through liquids handling specialists Pump Engineering, and includes a wide range of options, such as the RC250 model.

The valves are available in a range of materials including, stainless steel, Hastelloy, Monel and titanium and will handle flows from 100 lit/hour up to 8000 lit/hour, at pressures up to 9 Bar. RC250 valves feature; Linear or equal % trims, Hastelloy C and Tantalum trims, Kynar trim Cv’s from 6.0 to 0.05 and metallic trim CV’s from 6.0 to 0.0000018. The valve is available in sizes ¼”, ½”, ¾” and 1” with NPT or wafer style connections and a  choice of Teflon CV rings or REK packing is available. Control options include pneumatic and electric actuators.

The RC250 (807) barstock model is also available in PVDF and  will therefore withstand a wide range of corrosive media occurring in water treatment, chemical feed, pH control, semiconductor and pulp & paper applications. These type of applications could involve aggressive fluids such as; sodium hypochlorite, chlorine dioxide, sulphuric acid, sodium chlorate, ammonium fluoride and hydrochloric acid, all of which can be safely handled by the RC250 PVDF valve

Emerson Process Management announces the release of the Fisher GX 3-way control valve and actuator system.  The new GX 3-way has the ability to accurately control the temperature of water, oils, steam, and other industrial fluids.  Applications include heat exchangers and lubricating skids.

The flow cavity of the GX 3-Way valve body has been engineered to provide stable flow and reduce process variability.  This linear stability is perfectly suited for temperature and pH control applications.  The GX 3-way valve is multi-faceted in its ability to cover both flow mixing (converging) and flow splitting (diverging) applications with no extra parts needed.  Unlike other 3-way valves, it features both side-port and bottom-port common trim.

The GX 3-way valve package addresses the space limitations of the OEM industry.  It meets the requirements of both EN and ASME standards.  In addition, it is available with a complete accessory package, including the FIELDVUE DVC2000 integrated digital valve controller.  The GX 3-way is rugged, reliable, and easy to select.  Internal valve trim is designed to ensure long service life and avoid unnecessary maintenance.

I am writing to support the re-election of Ron Walter for Chelan County commissioner. I know Ron from the private and public sector and have always found him caring and very open to receive constituents’ input. He assembles the facts and makes sound decisions for our county. He is an honest and conscientious man, so why consider a change?

Keith Kuechmann

Wenatchee

Largent a wise choice

I live in Douglas County but own property in Chelan County, where voters now have the unique opportunity to voice a necessary change in the commissioners’ office. Recently Ron Walter, as commissioner, sought amendment of the definition of a “winery” under the Chelan County Code, as a favor to Saint Laurent Winery, owned by Mike and Laura Mrachek. This was after a hearing examiner correctly determined that the winery failed to meet the county regulatory definitions for that type of business, and was operating improperly.

Saint Laurent has been out of compliance with several of the original approved operating conditions established by the hearing examiner over three years ago, and has made little effort to become compliant. Rather, the Saint Laurent owners decided it a wiser investment to quickly become contributors to the Walter re-election campaign. (Source: Washington Public Disclosure Commission.)

This scenario underscores what decent citizens find most distasteful (vinegar rather than wine) about our elective process: the giving of political favor in exchange for campaign money. Put another way, Walter has sought to retroactively legalize prior improper operation of Saint Laurent, while rejecting the rule of law protecting surrounding property owners.

In exchange, Walter received money from those benefitted, the Mracheks. If you condone this kind of behavior, vote to retain Mr. Walter, because you certainly have a right to expect more of the same. But if you think that more of the same isn’t a wise moral choice or good planning practice, perhaps you should vote for Chuck Largent.

Scott Kane

East Wenatchee

Recount proof

Eastern Washington voters need to remember that we actually elected Dino Rossi as governor in 2004, twice! This was an amazing accomplishment considering how far left the Puget Sound region is. This will probably be our last chance to elect Dino or any other fiscal conservative as governor to give us a chance to avoid bankruptcy. If you want to see where we are headed with four more years of one-party control, just look at California. We will be broke and their answer will always be to increase spending and raise taxes. What businesses would want to locate here? Don’t forget, Gregoire plans to convince us we need a state income tax too!

Dino Rossi is an honest man who understands how to balance a budget, not a life-long politician serving special interests.

We need a recount-proof margin of victory to keep this election from being stolen again. Call your friends and relatives, drive people to vote, whatever it takes. Eastern Washington can make a difference if we stick together and vote for the best person for governor at this dangerous time — Dino Rossi!

Scott Hudson

Moses Lake

More change, please

Please vote on Nov. 4, and I would like to encourage you to vote for the Obama/Biden ticket. I ask this so that it might help my finances. Let me explain that I have been unemployed for the last four years, mostly by choice, so that I might migrate to a warmer climate during the cold months in Washington. I could not help but be excited by Sen. Obama’s comment about “spreading the wealth around,” and I for one could use a bit of the working persons’ wealth while I lounge on the beach.

So please keep working so that I might share in the fruits of your labor. Please don’t concern yourself over Sen. Obama’s lack of world experience or knowledge of our 57 states or the corrupt past of his associates, as I am more concerned about change, that change being the change of your money to my pocket.

Ron L. Schmidt

Riverside

Stick to news

I was dismayed that The Wenatchee World chose to run a front page story about the Wenatchee teacher who resigned after drinking on the job (The World, Oct 22).

The fact that she was intoxicated at work indicates that there is a significant problem of alcoholism with her. While there is much social stigma attached to alcoholism, it is a disease. It is extremely difficult to deal with.

Anyone who has dealt with the illness, and is still dealing with it, as well as anyone who has family or friends who are dealing with it, know that it is a day-by-day struggle. It results in great anxiety and pain for all involved.

It is certainly not appropriate fodder for discussion in public.

I can only hope that The World will refrain from such publications in the future and stick to real news.

Terry Fitzpatrick

North Central WEA UniServ

It’s capitalism that made us

It continuously amazes me the number of young and older adults who think business is bad, greedy and not paying taxes.

Small and large businesses are what make the wheels go round in this country. They contribute to the gross domestic product, create jobs, pay taxes, Social Security, unemployment, workers compensation etc., and make it possible for the “service industry ” — i.e., teachers, government, medical — to even exist.

Business has acquired a bad name because of the few CEOs, mainly in the finance world who have been greedy and produce nothing, simply shuttle figures and paperwork.

The CEO of Corning for five years drew zero compensation until Corning was “back on track.” Most business compensation is based on performance, as it should be for teachers, government employees, etc.

The media tend to print the negating or exceptions, but keep in mind, if it were not for the Alcoas, Comings, GMs, etc., in this country, we all would be drawing food stamps.

Please pass this information on to your children and teachers in our schools who sometimes have no clue as to what it takes to cut their paychecks. Again, capitalism is what has made this country great and the envy of the entire world.

Tom Hohn

Wenatchee

All letters must include the author’s signature, address and telephone number. There is a 300-word limit, and all letters are subject to editing.

Send letters to The Safety Valve, Box 1511, Wenatchee, WA 98807.