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This article is all about valves, and the various types of valves and fittings available. Valves are mechanical or electro-mechanical devices that are used to control the movement of liquids, gases, powders, etc. through pipes or tubes, or from tanks or other containers. In most instances, valves rely on some form of mechanical barrier—a plate, a ball, a diaphragm, for example—that can be inserted and removed from the flow stream of the material passing by. Some valves are designed as on-off varieties, while others allow very fine control of the passage of media.
Isometric drawing of a typical quarter-turn manual valve with bolted flanges.Image credit: cherezoff/Shutterstock.com
Material selection plays an important role in specifying valves to ensure the compatibility of the wetted parts of the valve with the fluid or powder passing through it. Sizing is determined by the pipe or tubing diameter, flow rate, and the width between flanges for pipeline valves being installed as replacements.
Aerosol Valves are used for dispensing the contents of aerosol cans. They consist of two primary components, the housing and the stem. Key specifications include the intended application, actuator type, output type, valve size, and materials of construction. Media dispensed can be a consideration as well. Aerosol valves dispense liquids, creams and ointments, gases, cleaning agents, and any other product that is packaged in an aerosol can.
Air Logic Valves are mechanical or electro-mechanical devices used to regulate the flow of air in pneumatic systems and can be used in place of electrical control in instances such as hazardous atmospheres or where electrical control is impractical. Key specifications include actuator type, number of ports, materials of construction, switching speed, port thread size, pressure ratings, and input voltage. Air logic valves are applied to pneumatic systems as e-stops, pilot valves, one-shot valves, etc.
Balancing Valves are used to control fluid flow by dividing flow evenly in multiple flow branches. Key specifications include the number of ports, port connections, valve size, and materials of construction. Balancing valves are used primarily in HVAC applications and fluid power systems. For example, they can be used in commercial heating/cooling systems to adjust water temperatures under varying loading conditions. They can also be used to provide a counterbalancing force for double acting cylinders.
Ball Valves are quarter-turn valves incorporating ported spheres that swivel in the pipe stream to either block, or allow, flow. Special designs are available which enable a degree of flow regulation. Key specifications include the number of ports, port configuration, port connections, valve size, and the materials that make up the valve body, its seat, seal, and stem packing. Ball valves are used practically anywhere a fluid flow must be shut off, from a compressed-air line to a high-pressure, hydraulic system. Ball valves can provide low head-loss characteristics as the port can exactly match the pipe diameter. Ball valves also tend to seal better than butterfly valves, but they can be costlier to purchase and maintain. Typically they are actuated with a lever which provides a visual indication of the valve status.
A ball valve in section, showing the full-diameter port that permits unrestricted flow.Image credit: Marina Demkina/Shutterstock.com
Blind Valves, or line blind valves, are mechanical devices used to stop flow through a pipeline. They are used primarily by the oil and gas industries as a means of isolating sections of a pipeline. Thes valves are also known as Piping Blinds. Key specifications include valve type, actuator type, port connections, valve size, as well as the material of the valve body, its seat, seal, and lining. Blind valves are common on ships and offshore platforms. They provide a visible, immediate indication as to whether a pipe is open or closed and are used to isolate portions of a pipeline to allow maintenance.
Butterfly Valves are quarter-turn valves which employ center-mounted circular flaps that swing into, and out of, the flow stream. Key specifications include port connection, valve size, and the materials that make up the valve body, its seat, seal, disc, and stem packing. Butterfly valves are used in wastewater plants, power plants, and process plants for shut-off and for regulating and isolating service and are especially popular in very large diameter pipelines. Generally smaller and cheaper than a ball valve of the same capacity, butterfly valves can be difficult to operate against high pressure and flow. They are also more leak-prone than ball valves and subject to higher head losses.
Butterfly valve with a worm-drive actuator provides increased closing/opening torque.Image credit: Yuthtana artkla/Shutterstock.com
Cartridge Valves are used to control flow in hydraulic and pneumatic fluid power systems. Their cartridge design allows them to be plugged into common manifolds and thus save weight and cost over discrete valve mounting. Key specifications include the intended application, valve type, actuator type, number of ports, valve size, and the materials of the valve body, its seat, seal, lining, and stem packing. Cartridge valves can be used in any of the common fluid power applications for which ordinary hydraulic or pneumatic valves serve, including check, directional control, flow control, logic, pressure control, motor control, etc.
Casing Valves are used exclusively by the oil and gas industry to provide access to well casings. Key specifications include the intended application, actuator type, port connections, valve size, and materials of construction.
Check Valves permit fluid to flow through them in one direction only. Lift-type check valves are similarly constructed as globe valves and use a ball or piston, often backed by a spring that opens under a specified pressure but closes as the pressure decreases, thus preventing backflow. These valves are often suited for high-pressure applications. A variant is the stop check valve which doubles as a shut-off valve.
Swing check valves employ hinged gates, disc wafers, or wafers that are often spring-actuated to close against ports as pressure diminishes. These devices can be effective in low-pressure applications. A tilting disc check valve varies the theme somewhat by hinging the gate slightly inward to reduce the pressure required for opening. Butterfly or double door check valves use two half-circle gates or wafers that are hinged at the centerline of the valve port and open downstream in the direction of flow.
Rubber check valves are also available and include designs such as the flap and duckbill varieties. Check valves are used on gas lines, for air service, and with pumps—anywhere that fluid needs to move in a single direction. They can be miniaturized, manufactured in plastic, and may incorporate many special features such as metal seats.
Christmas Tree Valves are mechanical devices used for controlling the flow of media coming from wells or other systems. Key specifications include the intended application, number of ports, as well as the pressure and temperature ratings. Christmas tree valves are used primarily in the oil and gas well application and are typically mounted to the head of the well for shutoff or controlling the flow of the media. They are usually custom fabricated.
Cock Valves are used for draining tanks and the like and often incorporate a threaded means for opening and closing. They are also used as low-pressure shut-offs where they typically use a quarter-turn lever. Key specifications include valve type, port connections, valve size, and materials of construction. Cock valves are used in a range of product applications, including radiators, heaters, tanks, boilers, laboratory glassware, air systems, tanks, drums, etc.
Diaphragm Valves employ flexible membranes to close off flow in pipes. Like pinch valves, the diaphragm completely seals off the actuating means from the process fluid, a benefit for valves in sanitary service. Key specifications include port configuration, port connections, valve size, media, and seal material. Diaphragm valves are used mostly in the pharmaceutical, cosmetics, food, and semiconductor industries. Sometimes control valves that are actuated with pneumatic diaphragms are incorrectly called “diaphragm valves.” The reader is cautioned to make this distinction.
Disc Valves are mechanical devices used to control flow through a pipe. A disc valve consists of a round flat plate mounted to the end of a stem that enters the pipe at 45 degrees to the pipe longitudinal axis. Rotating the stem through a half circle opens or closes the pipe. Disc valves are almost exclusively found in food processing applications. Key specifications include valve type, actuator type, port connections, valve size, and the materials of construction. Disc valves are used in food, pharmaceutical, and dairy industries to for shut-off service of liquid, powder, or food slurries where sanitation is critical.
Double Block and Bleed Valves are mechanical or electro-mechanical devices consisting of dual inline blocker valves and single bleeder valves in common valve bodies and used for isolating fluid lines from upstream pressure. Key specifications include the intended application, actuator type, port connection type, flow coefficient, media, pressure rating, as well as the features. Double block and bleed valves are used primarily in process control applications for the purpose of shutting off the upstream pressure and bleeding off the fluid and/or pressure of the system. They may be manually operated or controlled by an electro-mechanical actuator. Media may include, water, chemicals, gases, oil, steam, or other similar fluids.
Engine Valves are used in engines to seal between combustion chambers and either the intake or exhaust systems. Key specifications include the intended application, head and stem diameter, and the material. Opening and closing of engine valves are controlled by a series of cams and springs. They are available in several materials and types depending on the application which may include automobiles, trucks, motorcycles, etc. with special designs available for racing applications.
Faucet Valves are used for controlling fluid flow into basins or sinks and typically lack outlet connections, though some are equipped with threads for connecting hose, often called a hose bibb or spigot. Key specifications include valve type, actuator type, port connections, valve size, and the material that make up the valve body, which includes its seat, seal, lining, and stem packing. Mounting type is another consideration.
Faucet valves are used in laboratories, on drums, as hose bibbs, and can be made of inexpensive materials that can be discarded once a container's contents are emptied.
Float Valves are mechanical devices which use hollow spheres or other shapes mounted on levers or tracks which open and close fluid inlets. A float valve is used primarily for maintaining fluid in a tank at a specific level. Key specifications include the intended application, port connections, valve size, float size, and the materials that make up the valve body, its seal and float. Float valves are used in bathroom toilets to replenish the water level after a flush and in many tank-level control systems.
Gate Valves are used mainly for blocking fluid flow and are less likely to be employed for flow regulation. A gate valve uses a plate-like barrier that can be lowered into the flow stream to stop the flow. Its operation is similar to that of a globe valve except the gate provides less flow restriction than with a globe-valve plug when the valve is in the fully opened position. Key specifications include port configuration, port connections, valve size, and the materials that make up the valve body, its seat, seal, lining, and stem packing. Gate valves can use wedge-shaped plugs or parallel plates. Plugs usually seal both the up and downstream sides of the valve while plates usually only seal on the upstream face. Wedges can take on a variety of design alternatives that reduce or accommodate wear of the sealing surfaces. Although the advantage of gate valves is their reduced head loss when open compared to globe valves, they are not useful for throttling and may not produce the positive shut-off that globe valves provide. Gate valves are used in wastewater plants, power plants, and process plants for shut-off and for isolating service.
Gate valves are usually designated as rising-stem and non-rising stem designs. The advantage of rising-stem valves is that they permit easy visualization as to whether a valve is open or closed. The advantage of the Non-Rising Stem, or NRS valves, is that the stem is protected from exposure to corrosive or other environmental conditions by the valve bonnet. Neither design has much impact on the actual valve function.
Globe Valves, named for their spherically shaped valve bodies that were at one time common, are also named for their use of a globe-shaped disc that constricts flow by closing against a restricting orifice. The disc is opened and closed with a handwheel on manually operated valves and with an actuator and sliding shaft on automatic valves. Key specifications include valve type, port configuration, port connections, valve size, and the materials that make up the valve body, such as its seat, seal, lining, and stem packing. Globe valves are used for shut-off and regulating, and are used in wastewater plants, food processing facilities, and process plants, for example. The most common variety is the Z-style valve, so-called because of the path which the fluid follows through the valve body. These two right-angle turns that the fluid must make through the valve account for the design’s relatively high head losses. A less restrictive design is the Y-style valve, which orients the valve stem at 45° to the valve body. Another style is the angle valve, which turns the flow 90°.
The shape of the disc can be varied to produce a valve that goes to full-flow quickly, or, by using a more tapered plug design, produce a valve that can precisely regulate flow.
Globe valves can seal against the fluid flow or with it, depending on the requirements of the installation (i.e. fail closed vs. fail opened) and the choice plays a major role is sizing an actuator. Like gate valves, globe valves can be rising-stem or NRS varieties.
A typical Z-shape globe valve in section, showing the two turns the fluid must make through the body.Image credit: Surasak_Photo/Shutterstock.com
A typical Y-shape globe valve is less restrictive to fluid flow than the Z-shape valve.Image credit: PHOTOCREO Michal Bednarek
Hydraulic Valves are mechanical or electro-mechanical devices used to control fluid flow in hydraulic fluid power systems. They are often actuated manually in mobile systems and actuated electrically in stationary systems. Key specifications include valve type, actuator type, port connections, number of ports, port configuration, materials of construction, and pressure ratings. Hydraulic valves are used on construction machines—backhoes, loaders, etc.—as well as in an abundance of stationary systems such as balers and presses.
Hydraulic valves
Image credit: Metro Hydraulic Jack Co.
Needle Valves are used to meter fluid flow through tubing or ports. Flow is regulated by inserting or withdrawing a tapered stem into or out of a similarly tapered orifice, creating a very precise way of adjusting fluid flow through the orifice. Key specifications include valve type, port connections, valve size, and the materials that make up the valve body, which includes its seat, seal, lining, and stem packing. Needle valves are used in vacuum systems and for metering systems where precise flow regulation is required. Because of the high number of turns required to close a needle valve, they are not ideally suited for use in shut- off service applications.
Pinch Valves are mechanical devices used to control fluid and dry-product flow through pipes. A pinch valve uses a flexible tube that serves as a conduit, which can be squeezed shut through the use of air or fluid pressure against its outer surface. It can be actuated mechanically as well. Key specifications include valve size and the material used in the tube. In a pinch valve, the tube itself is the only material in contact with the product in the pipe. Pinch valves are used for flow regulating and shut-off of food slurries, dry products, sand, gravel, and the like.
Piston Valves are mechanical devices used to control fluid flow through a pipe. A piston valve uses a cylindrical plug to close off flow through the valve and is typically used for isolation service. Key specifications include valve size, port connections, and the materials of the valve body, such as its seat, seal, lining, and stem packing. Piston valves are used for isolation service in steam, condensate, and other liquid systems.
Plug Valves are quarter-turn valves used to control fluid flow through a pipe. A plug valve constricts flow similarly to a ball valve, using a ported plug rather than a ported ball that swivels in the flow stream to constrict or allow flow. Key specifications include valve type, port configuration, port connections, valve size, and the materials that make up the valve body, as well as its seat, seal, lining, and stem packing. Plug valves are used for shut-off and are used as control valves for the chemical process industries, processing plants and wastewater treatment facilities, for example. A distinction is made between lubricated plug valves, which inject a lubricant between the plug and valve body to act as a sealant, and unlubricated types, which instead rely on a polymeric sleeve for sealing and friction relief.
Poppet Valves are mechanical or electro-mechanical devices used to control air flow to pneumatic cylinders. The term “poppet” also describes a kind of check valve. Engine valves are also sometimes called poppet valves. Key specifications include valve type, valve size, materials of construction, flow coefficient, and pressure ratings. Poppet valves are used in pneumatic systems and can be controlled with pilot air or electrically with a solenoid.
Image credit: Dmitrii Pridannikov/Shutterstock.com
Relief Valves protect pressurized systems such as boilers or piping from over-pressure conditions, usually by way of a spring-loaded diaphragm. They can relieve internal pressure as well as external pressure caused by vacuum formation within a tank, for example. Key specifications include valve type, port connections, valve size, pressure rating, intended application, and the materials of construction.
Relief valves are used on pneumatic compressors, on gas lines, and in cryogenic systems — in short, anyplace where over-or under-pressure conditions can occur. Pressure and vacuum relief valves operate automatically but can have a manual means of actuation for testing. Atmospheric relief valves are used on condensers. A surge control valve is a kind of relief valve intended to reduce damage to hydraulic systems from a phenomenon known as a hydraulic surge.
Rotary Valves are sometimes called rotary airlocks and are used mainly for dispensing powders and other dry, flowable products. Hopper valves are closely related, used to dispense dry products from hoppers and similar dry-storage containers.
Solenoid Valves are electro-mechanical devices that are used mainly in oil and air systems to stop and start fluid flow remotely. They depend on electro-mechanical solenoids for direct or piloted operation. They are not generally used for proportional flow control. Key specifications include valve type, number of ports, port configuration, port connections, valve size, materials of construction, pressure ratings, and input voltage. Solenoid valves are used to actuate hydraulic jacks, control the hydraulic cylinders on trucks, and control the flow of water, oil, or solvents through piping systems. They are used extensively in pneumatic systems as well. A solenoid latching valve is designed to lock an air valve into position without requiring that power be maintained at the solenoid.
Solenoid valves can be used to direct air to pneumatic devices such as this air-actuated assembly fixture.Image credit: asharkyu/Shutterstock.com
With some exceptions (for instance, aircraft fuel valves or refrigeration valves) 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.
Pipeline valve sizes usually correspond to flange dimension for various standard pipe sizes and pressures, i.e., 150 psi, 300 psi, etc. ANSI B16.10 lists face-to-face dimensions for ferrous flanged and welded end valves in steam, hydraulic, and high-temperature service.
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.
A pneumatic actuator atop a globe valve is sandwiched between two manual globe valves.Image credit: engineer story/Shutterstock.com
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. Instead, actuators work on flexible, usually rubber, elements which open and close the valve passages, and eliminate the need to insert metal parts into the fluid stream and the packings, that go along with them.
Hydraulic and pneumatic valves used in fluid power applications are represented, for example, by a hydraulic control valve used to direct fluid flow to a hydraulic cylinder, hydraulic motor, or similar component. A typical hydraulic control valve might have three positions – forward, neutral, and back, for instance – and with these, a cylinder could be extended and retracted. Often the valves have some degree of flow control to vary the speed at which the controlled device moves. A popular name for some hydraulic and pneumatic valves is spool valves, owing to a spool-like member that shifts inside the valve body to open and close ports. Another kind is a hydraulic diverter valve, so named because it allows an operator to switch between systems that are not used simultaneously, reducing the number of discrete components needed for any given system. A solenoid actuated air valve uses a solenoid to open a small pilot valve that in turn opens (or closes) the valve output ports. Air valves such as this are used in automated machinery of all kinds to operate cylinders, rotary devices, and end-of-arm tooling, for example. Air is also used in hazardous locations to operate full-size valves in a fail-safe manner, such as pneumatic tank shutoff valves employed on tank farms.
In selecting pipeline valves, an important consideration is whether the valve will be used for start-stop operations or for throttling. Water hammer—i.e., a surge in pressure or change in momentum caused when a moving fluid suddenly stops or changes direction—which may result from such operations can cause damage to the valves and equipment involved. Choosing a valve design which minimizes water hammer can mitigate the level of damage suffered by the system and its components, and reduce the risk of complete failure.
Another important consideration is the nature of the fluid that will flow through the valve. Fluids that contain particulates can have abrasive effects on valves whose mechanisms are exposed to the fluid, a butterfly valve, for instance. And for these fluids, a ball valve is a better choice owing to the uninterrupted path it presents to the fluid. Corrosive fluids such as chlorine add further complications to materials selection.
Actuation is another topic that may or may not be of concern. A simple ball valve in a small laboratory or in a residential setting may need nothing more than a quarter-turn lever. A large gate valve in a process pipeline may need electric or pneumatic actuation and all the electronics associated with controlling it.
Valve actuation depends on the valve type. Ball valves, for instance, are usually opened and closed with a lever because the ball turns only a quarter revolution between the two positions. A globe valve will often employ a handwheel which works on a lead screw to raise and lower the globe valve plug out of and into the orifice. In large valves, a reduction gear may augment the handwheel to provide the operator some mechanical advantage when opening or closing the valve. Pipeline valves generally fall into one of these two types.
The face-to-face dimensions of valves are critical when considering a replacement.Image credit: RachenStocker/Shutterstock.com
An important consideration when replacing a valve is the face-to-face distance between flanges, which can be clearly seen in the image above. Generally, a valve needs to fit in the space between fixed pipes so this dimension can be critical if modifications to existing piping are undesirable and are to be avoided. Some manufacturers will offer their valves as direct dimensional replacements for valves of other types.
In their larger sizes, valves typically adhere to the standardized ASME flanges for their connections. In smaller sizes, the connections can vary from sanitary (Tri-clamp type) to compression type.
Ports and ways refer to the number of passages into the valve, and for most pipeline valves there are two. Ball valves are routinely available with three or more ports and use a ball that has an “L” shaped passage.
Hydraulic valves are generally controlled automatically on stationary industrial machinery and manually on mobile machines. Cartridge designs are available for either venue. Hydraulic valves are often mounted in common manifolds or ganged together as valve stacks to simplify plumbing and reduce space requirements. Some hydraulic valves are designed as monoblocks, meaning the multiple valve body is cast as a single unit.
Air logic valves represent the analogous version of hydraulic valves which use air as the fluid (instead of oil) and are as ubiquitous in factory/manufacturing operations as hydraulic valves are in mobile systems. Many of the same considerations for hydraulic valves are paralleled in the world of air logic valves.
Types of Valves and Fittings -
Important AttributesCv relates to flow through the valve body and represents the number of gallons of water per minute at 60oF that can pass through the valve with a 1 psi pressure drop across the valve. It is a common method of comparing valve performance.
Valve sizes in both inches and millimeters generally correspond to the size of the pipes they work with. Flanges, etc. are usually sized based on the valve size.
Valves are often rated according to ANSI classes of 150 psi, 300 psi, etc., corresponding to standard pipeline ratings. Domestic ball valves can be rated as high as 600 psi.
True union refers to the connections on a valve body which allows it to be inserted in a pipeline without moving the pipes apart. This is common for small ball valves where the pipe connections are often threaded. Single union valves have this connection on only one side. Compression fittings also apply mainly to small valves used with tubing of copper, plastic, etc. Flanges are common port connections in larger valves. Connections can be brazed in many smaller valves used for water service. Plastic valves can have socket connections for solvent welding.
Valves are often deemed as being bubble-tight, a description for valves which will not allow any liquid passage upon closure. Certain designs are more apt to be bubble tight than others, particularly those valves that are intended for on-off service versus those that are used mainly for regulating flow.
Valve standards are almost too numerous to list but the reader is directed to various standards organizations such as ASME, ANSI, and API for their comprehensive collections of pipeline and valve standards. A sampling includes:
This guide provides a basic understanding of valves and their selection and uses in various environments such as hydrogen applications. For more information on related products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources or view details on specific products.
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