Solenoid valves may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control. A spring may be used to hold the valve opened or closed while the valve is not activated.
A- Input side B- Diaphragm C- Pressure chamber D- Pressure relief conduit E- Solenoid F- Output side
A- Input side
B- Diaphragm
C- Pressure chamber
D- Pressure relief conduit
E- Solenoid
F- Output side

In some solenoid valves the solenoid provides the full power for the operation of the main valve while there is a certain type where the solenoid, using very little power, controls a secondary pilot valve and it is the pressure of the fluid itself which provides the power for the actuation of the main valve. These types of valves are commonly used in washing machines, gardening and similar uses.

The diagram to the right shows the design of one such valve. If we look at the top figure we can see the valve in its closed state. The water under pressure enters at A. B is an elastic diaphragm and above it is a weak spring pushing it down. The function of this spring is irrelevant for now as the valve would stay closed even without it. The diaphragm has a pinhole through its center which allows a very small amount of water to flow through it. This water fills the cavity C on the other side of the diaphragm so that pressure is equal on both sides of the diaphragm. While the pressure is the same on both sides of the diaphragm, the force is greater on the upper side which forces the valve shut against the incoming pressure. By looking at the figure we can see the surface being acted upon is greater on the upper side which results in greater force. On the upper side the pressure is acting on the entire surface of the diaphragm while on the lower side it is only acting on the incoming pipe. This results in the valve being securely shut to any flow and, the greater the input pressure, the greater the shutting force will be.

Now let us turn our attention to the small conduit D. Until now it was blocked by a pin which is the armature of the solenoid E and which is pushed down by a spring. If we now activate the solenoid, the water in chamber C will flow through this conduit D to the output side of the valve. The pressure in chamber C will drop and the incoming pressure will lift the diaphragm thus opening the main valve. Water now flows directly from A to F.

When the solenoid is again deactivated and the conduit D is closed again, the spring needs very little force to push the diaphragm down again and the main valve closes. In practice there is often no separate spring, the elastomer diaphragm is moulded so that it functions as its own spring, preferring to be in the closed shape.

From this explanation it can be seen that this type of valve relies on a differential of pressure between input and output as the pressure at the input must always be greater than the pressure at the output for it to work. Should the pressure at the output, for any reason, rise above that of the input then the valve would open regardless of the state of the solenoid and pilot valve.

A common use for 2 way solenoid valves is in central heating. The solenoid valves are controlled by an electrical signal from the thermostat to regulate the flow of heated water to the heating elements within the occupied space. Such valves are particularly useful when multiple heating zones are fed by a single heat source. Commercially available solenoid valves for this purpose are often referred to as Zone valves.

These new solenoid valves provide significant weight and space advantages for use on new generation lightweight and compact subsea control systems. Specifically designed for Oil & Gas Deepwater Drilling, Production, and Intervention Systems. The Company is looking forward to new ventures in Subsea Processing.

The solenoid valves are specifically created for harsh environment applications. The sealed construction of the solenoids conforms to IP68 of IEC529 standards for continuous immersion in water in ambient pressures to 4,500 psi (10,000 ft ocean depth). In addition, the solenoid valves are corrosion resistant in seawater, internally and externally.

The new Model 1719-100 environmentally sealed Solenoid Valve is a latching model, for an operating pressure of 3,000 psi differential, and having a flow capacity of 0.1 inch ESEOD. The solenoids are rated at 3.0 amp @ 24vdc and are provided with underwater connectors. Major advantages of this miniature series are its small size, low weight (only about 3.5 lbs), and low power.

Such emergency shutdown (ESD) shut-off valves are usually activated by a solenoid valve and are also equipped with limit switches for position feedback. Not surprisingly in ‘normal’ production situations, ESD shut-off valves remain unused, typically fixed in one position for many months or even many years.

Special test procedures have been developed and are used in most production environments which offer an effective and practical method for testing shut-off valves to ensure they will work when needed.

For example, partial stroke testing is a common practice, allowing valves to be partially stroked for testing purposes, without causing major interruption or down-time to the production process.

As part of their on-going development of a wide range of control valves, positioners and accessories, Samson Controls offers a range of electro-pneumatic positioners.
Further reading

Building automation system with Ethernet
The Trovis Modulon Automation System can easily be integrated into existing corporate networks thanks to its Ethernet interface and the use of the standard TCP/IP protocol

Temperature controller with electric actuator
The Samson temperature control designed for application in instantaneous water heating systems helps to achieve hot water at a constant temperature straight out of any tap in a building

These include their Type 3730-3 model which has been enhanced and incorporates an ESD function to enable partial stroke tests to be carried out, without disrupting the process line.

The positioner can be mounted on the valve in addition to the solenoid valve, or to replace it, and enables the valve to be moved precisely to follow the set point within the valve working range.

The partial stroke test is completely integrated into the positioner to detect a sticking valve, caused for example, by corrosion.

Test schedules are flexible and can be prolonged if necessary to suit specific application requirements, while test validation can be performed simply by using the corresponding instrumentation and initiating it over a commonly available SIS logic solver.