Uses of Valves

Posted by sere on June 28th, 2021

Some custom valves are not industry specific; they can be used across a wide range of industries, including chemical processing, food and beverage, gas transmission, mining, oil and gas, and power generation.

Some are dedicated to fluid power applications, including solenoid, poppet, hydraulic, cartridge, and air logic valves. Others are for general pipeline applications or smaller-scale fluid systems and include plug, piston, pinch, globe, gate, disc, diaphragm, butterfly, and ball valves. Then there are valves designed to activate automatically in certain events including relief valves and check valves.

Some valves are so common that they are grouped by function, for example, boiler feedwater and blowdown control valves, faucet valves, float valves, double block and bleed valves, HVAC zone valves, or floor drain check valves. Some valves are so specialized that they may have only one or two applications, such as rotary solenoid valves used in excavators, or inverted vent check valves used in sewage systems and on ships.

As for pipeline valves, many can be thought of as suited either to blocking or throttling. A ball valve is better suited for on-off applications than it is for regulating flow. The same goes for gate and piston valves. For flow regulating, globe and butterfly valves are preferred choices, with globe valves being especially common. Ball valves can be designed so that friction loss through an open valve is no greater than what would be encountered in a like diameter pipe (also making them piggable in some cases). Other valve types usually introduce some loss in the valve owing to the need to place the components of the valve, actuating shafts, etc. directly in the stream and/or the need to redirect the direction of fluid flow.

Most pipeline valves are available with manual levers or handwheels which can be adapted to gear type actuators in larger sizes and fitted with electric or electro-pneumatic actuators for automatic control. Valves fitted with such actuators are sometimes called control or flow control valves in that with automatic actuation they can be integrated into control loops used for process automation. The phrase “control valve” is sometimes used to describe the valves used in hydraulic and pneumatic fluid power systems to actuate a ram, for example. Any valve can be a control valve, that is to say.

Any valves fitted with automatic actuators could be considered control valves, as they presumably would be tied in with remote process controllers. The same valve without the actuators would still be a globe valve, gate valve, etc. albeit one with manual control via handwheel or lever. Many control valves retain some form of manual control by which the valve can be opened and closed. Some valves are considered control valves if they have mechanical means of sensing flow rate, pressure, etc. and can adjust the valve through pilots, for example. In the smaller sizes, solenoid valves function as control valves. Many manufacturers will provide integrated valve and actuator combinations, for example, motorized ball valves.

Valve material can play an important role in valve selection especially when it comes to handling aggressive fluids, abrasive slurries, food products, and so on. Material concerns address not only the wetted parts but can extend to the materials of the valve body too. For instance, valves used for food processing need to resist caustic washdown chemicals and usually demand stainless steel even for exterior parts that do not contact the product. Some valves are lined to improve their resistance to corrosive fluids, etc. Check valves are sometimes lined with PTFE for improved operation and wear resistance. Valves are available in the smaller sizes in a host of plastics and find use in many laboratory applications. Ball valves, for example, are available in brass, stainless steel, polypropylene, and other plastics. So-called sanitary valves are fitted with quick disconnect flanges so that they can be removed from the pipeline easily for internal sanitizing, and are especially popular in the ball, butterfly, and plug designs. The valves themselves often have features which enable quick disassembly and reassembly. Two popular valve styles which use no contacting metal parts in the fluid are the diaphragm and the pinch valves.