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Steam valves are used to control the flow and pressure level of steam and heated water vapor. They are usually made of aluminum, brass, bronze, cast iron, ductile iron, copper, steel, or stainless steel. There are several basic types of products. Angle valves position the inlet and outlet at 90° to provide maximum flow. Ball valves offer tight shutoff, predictable control, and ease of operation. Bellows valves feature a contaminant free, positive shutoff for high-purity gas and fluid systems. Butterfly valves control flow through a circular disc or vane by turning the valve’s pivot axis at right angles to the direction of flow in the pipe. Cartridge valves are directional control valves which are inserted into manifolds. Check valves are self-activating safety valves that prevent process flow from reversing. Diaphragm valves use an elastomeric diaphragm to separate the flow stream from the closure element. Gate valves or knife valves use a flat closure element to provide shutoff. Both pinch valves and globe valves provide on/off control and throttling service. Plug valves or stop-cock valves raise or lower a cylindrical plug within a seat to control flow. Poppet valves open and close ports with a sealing device composed of a disk, cone or sphere that is pressed against the seating surface using a spring. Other types of steam valves include regulators, servo valves, solenoid valves, spool valves, and toggle valves.

Specifications for steam valves include valve size, pressure rating, number of ports or ways, valve flow coefficient, and connection type. Valve size represents the size of the passage opening and is measured in English units such as inches (in) or metric units such as centimeters (cm). Pressure rating is the maximum pressure, usually measured in pounds per square inch (psi), for which products are rated. Valve flow coefficient is the number of gallons per minute of at which 60° F water flows through a valve at a specified opening with a pressure drop of 1 psi across the valve. There are many different connection types for steam valves. Threaded valves have internal or external threads for inlet or outlet connections. Compression fittings do not require soldering or threading because tightening the nut on one fitting compresses a washer to form a watertight closure. Some steam valves have bolt flanges, clamp flanges, union connections, or tube fittings. Others have socket weld or butt weld connections. Valves with a metal face seal sandwich a metal gasket between two fitting parts.

There are many different actuation methods for steam valves. Manual devices are opened or closed via a hand-operated wheel or crank. Mechanical valves are actuated by an unpowered component such as a float or cam. Electric and pneumatic valves are commonly available. Electro-hydraulic servo valves produce hydraulic control in response to an electrical signal input. Similarly, electro-pneumatic servo valves produce pneumatic control in response to an electrical signal input. Thermally-actuated valves are activated by a change in temperature in the handled media. Typically, temperature and pressure relief occurs once a preset temperature is reached.

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