Valves

A valve is a device that regulates the flow of a fluid (gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. Valves are technically pipe Fittings, but are usually discussed as a separate category.

Valves are also found in the human body. For example, there are several which control the flow of blood in the chambers of the heart and maintain the correct pumping action. Valves are used in a variety of contexts, including industrial, military, commercial, residential, and transportation.

Oil and gas, power generation, mining, water reticulation, sewerage and chemical manufacturing are the industries in which the majority of valves are used. Valves may be operated manually, either by a hand wheel, lever or pedal. Valves may also be automatic, driven by changes in pressure, temperature or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or steam boilers. More complex control systems using valves requiring automatic control based on an external input (i.e., regulating flow through a pipe to a changing set point) require an actuator. An actuator will stroke the valve depending on its input and set-up, allowing the valve to be positioned accurately, and allowing control over a variety of requirements.

A huge variety of valves are available, and valves have infinite applications and sizes ranging from .004" (0.1 mm) to 24" (600 mm). Special valves can be manufactured to have a diameter exceeding 200" (5000 mm).

Valves can be categorized into the following design types, and although there are hundreds of variations, they all fit into these basic types:

• Gate Valves
• Poppet Valves
• Plug Valves
• Globe Valves
• Check Valves
• Butterfly Valves
• Diaphragm Valves
• Ball Valves
• Needle Valves
• Pinch Valves

Valves may be classified by how they are operated:

• Manual Valves
• Solenoid Valves
• Hydraulic/Pneumatic Valves

A gate valve, also known as a sluice valve, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar. The gate faces can form a wedge shape or they can be parallel. Gate valves are sometimes used for regulating flow, but many are not suited for that purpose, having been designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss.

Gate valves are characterized as having either a rising or a nonrising stem. Rising stems provide a visual indication of valve position. Nonrising stems are used where vertical space is limited or underground.

Bonnets provide leak proof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest, offering a durable, pressure-tight seal. Union bonnet is suitable for applications requiring frequent inspection and cleaning. It also gives the body added strength. Bolted bonnet is used for larger valves and higher-pressure applications. Another type of bonnet construction in a gate valve is pressure seal bonnet. This construction is adopted for valves for high pressure service, typically in excess of 15 MPa (2250 psi). The unique feature about the pressure seal bonnet is that the body - bonnet joints seals improves as the internal pressure in the valve increases, compared to other constructions where the increase in internal pressure tends to create leaks in the body-bonnet joint.

Gate valves normally have flanged ends, which are drilled according to pipeline compatible flange dimensional standards. Gate valves are typically constructed from cast iron, ductile iron, cast carbon steel, gun metal, stainless steel, alloy steels, and forged steels.

A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft called a valve stem. The shaft guides the plug portion by sliding through a valve guide. In most applications, a pressure differential helps to seal the valve and in some applications open it.

Poppet valves are used in much industrial process from controlling the flow of rocket fuel to controlling the flow of milk.

The semiconductor industry often uses ultra-clean poppet valves as isolation valves. Here is an animation of a generic poppet valve.

Plug valves are valves with cylindrical or conically-tapered "plugs" which can be rotated inside the valve body to control flow through the valve. The plugs in plug valves have one or more hollow passage ways going sideways through the plug, so that fluid can flow through the plug when the valve is open. Plug valves are simple and often economical.

When the plug is conically-tapered, the stem/handle is typically attached to the larger diameter end of the plug. Plug valves usually do not have bonnets but often have the end of the plug with the handle exposed or mostly exposed to the outside. In cases like that, there is usually not much of a stem. The stem and handle often come in one piece, often a simple, approximately L-shaped handle attached to the end of the plug. The other end of the plug is often exposed to the outside of the valve too, but with a mechanism which retains the plug in the body.

Slightly conically-tapered metal (often brass) plug valves are often used as simple shut-off valves in household natural gas lines.

A Globe valve is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body.

Globe Valves are named for their spherical body shape with the two halves of the body being separated by an internal baffle. This has an opening that forms a seat onto which a movable plug can be screwed in to close (or shut) the valve. The plug is also called a disc or disk. In globe valves, the plug is connected to a stem which is operated by screw action in manual valves. Typically, automated valves use sliding stems. Automated globe valves have a smooth stem rather than threaded and are opened and closed by an actuator assembly. When a globe valve is manually operated, the stem is turned by a hand wheel.

Globe valves are used for applications requiring throttling and frequent operation. For example, globe valves or valves with a similar mechanism may be used as sampling valves, which are normally shut except when liquid samples are being taken. Since the baffle restricts flow, they're not recommended where full, unobstructed flow is required.

Check valves, or non-return valves, are installed in pipeline systems to allow flow in one direction only. They are operated entirely by reaction to the line fluid and therefore do not require any external actuation. In this text, the expected, or desired direction of flow is termed 'forward flow', flow in the opposite direction is 'reverse flow'.

There are a number of reasons for using check valves, which include: Protection of any item of equipment that can be affected by reverse flow, such as flow meters, strainers and control valves.

• To check the pressure surges associated with hydraulic forces, for example, water hammer. These hydraulic forces can cause a wave of pressure to run up and down pipe work until the energy is dissipated
• Prevention of flooding.
• Prevention of reverse flow on system shutdown.
• Prevention of flow under gravity.
• Relief of vacuum conditions.

A diaphragm check valve uses a flexing rubber diaphragm positioned to create a normallyclosed valve. Pressure on the upstream side must be greater than the pressure on the downstream side by a certain amount, known as the pressure differential, for the check valve to open allowing flow. Once positive pressure stops, the diaphragm automatically flexes back to its original closed position.

A swing check valve is a butterfly-style check valve in which the disc, the movable part to block the flow, swings on a hinge, either onto the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle Although swing check valves can come in various sizes, large check valves are often swing check valves.

A clapper valve is a type of check valve used in firefighting, and has a hinged gate (often with a spring urging it shut) that will only remain open in the out flowing direction. A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. When the valve is open, it acts as a check valve, but the valve can be deliberately shut to stop flow.

A lift-check valve is a check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly. When the pressure is no longer higher, gravity or higher downstream pressure will cause the disc to lower onto its seat, shutting the valve to stop reverse flow.

A butterfly valve is a type of flow control device, typically used to regulate a fluid flowing through a section of pipe. The valve is similar in operation to a ball valve. A flat circular plate is positioned in the center of the pipe. The plate has a rod through it connected to an actuator on the outside of the valve. Rotating the actuator turns the plate either parallel or perpendicular to the flow. Unlike a Ball valve, the plate is always present within the flow, therefore a pressure drop is always induced in the flow regardless of valve position.

A butterfly valve is from a family of valves called quarter-turn valves. The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the process fluid. The valve may also be opened incrementally to regulate flow.

There are different kinds of butterfly valves, each adapted for different pressures and different usage. The resilient butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high performance butterfly valve, used in slightly higher-pressure systems, features a slight offset in the way the disc is positioned, which increases the valve's sealing ability and decreases its tendency to wear. The valve best suited for high-pressure systems is the tricentric butterfly valve, which makes use of a metal seat, and is therefore able to withstand a greater amount of pressure.

Butterfly valves are valves with a circular body and a rotary motion disk closure member which is pivotally supported by its stem. A Butterfly valve can come in various styles including eccentric and high-performance valves. These are normally a type of valve that uses a flat plate to control the flow of water. As well as this, Butterfly valves are used on fire apparatus and typically are used on larger lines, such as front and rear suctions and tank to pump lines. A Butterfly valve is also a type of flow control device, used to make a fluid start or stop flowin

through a section of pipe. The valve is similar in operation to a Ball valve. Rotating the handle turns the plate either parallel or perpendicular to the flow of water, shutting off the flow. It is a very well known and well used design.

• Resilient butterfly valve which has a flexible rubber seat. Working pressure 232 psi
• High performance butterfly valve which is usually double eccentric in design. Working pressure up to 725 psi.
• Tricentric butterfly valve which is usually with metal seated design. Working pressure
  up to 1450 psi.

Diaphragm valves (or membrane valves) consists of a valve body with two or more ports, a diaphragm, and a "saddle" or seat upon which the diaphragm closes the valve. The valve is constructed from either plastic or steel.

Originally, the diaphragm valve was developed for use in non-hygienic applications. Later on the design was adapted for use in the bio-pharmaceutical industry by using compliant materials that can withstand sanitizing and sterilizing methods.

There are two main categories of diaphragm valves: one type seals over a "weir" (saddle) and the other (sometimes called a "straight-way" valve) seals over a seat. The main difference is that a saddle-type valve has its two ports in line with each other on the opposite sides of the valve, whereas the seat-type has the in/out ports located at a 90 degree angle from one another. The saddle type is the most common in process applications and the seat-type is more commonly used as a tank bottom valve but exists also as a process valve. While diaphragm valves usually come in two-port forms, they can also come with three ports and even more. When more than three ports are included, they generally require more than one diaphragm; however, special dual actuators can handle more ports with one membrane.

Diaphragm valves can be manual or automated. Their application is generally as shut-off valves in process systems within the food and beverage, pharmaceutical and biotech industries. The older generation of these valves is not suited for regulating and controlling process flows, however newer developments in this area have successfully tackled this problem.

A ball valve is a valve that opens by turning a handle attached to a ball inside the valve. The ball has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. The handle or lever will be inline with the port position letting you "see" the valve's position. The ball valve, along with the butterfly valve and plug valve, are part of the family of quarter turn valves.

Ball valves are durable and usually work to achieve perfect shutoff even after years of disuse. They are therefore an excellent choice for shutoff applications (and are often preferred to globe valves and gate valves for this purpose). They do not offer the fine control that may be necessary in throttling applications but are sometimes used for this purpose.

Ball valves are used extensively in industry because they are very versatile, pressures up to 10,000 psi, temperatures up to 200 Deg C. Sizes from 1/4" to 12" are readily available They are easy to repair, operate manually or by actuators.

The body of ball valves may be made of metal, plastic or metal with a ceramic center. The ball is often chrome plated to make it more durable.

Multi-port ball valves with 4 ways, or more, are also commercially available, the inlet way often being orthogonal to the plane of the outlets. For special applications, such as driving air-powered motors from forward to reverse, the operation is performed by rotating a single lever 4-way ball valve. The 4-way valve has two L-shaped ports in the ball that do not interconnect, sometimes referred to as an "×" port.

Ball valves in sizes up to 2 inch generally come in single piece, two or three piece designs. One piece ball valves are almost always reduced bore, are relatively inexpensive and generally are throw-away. Two piece ball valves are generally slightly reduced (or standard) bore, they can be either throw-away or repairable. The 3 piece design allows for the center part of the valve containing the ball, stem & seats to be easily removed from the pipeline. This facilitates efficient cleaning of deposited sediments, replacement of seats and gland packings, polishing out of small scratches on the ball, all this without removing the pipes from the valve body. The design concept of a three piece valve is for it to be repairable.

A needle valve has a relatively small orifice with a long, tapered, conical seat. A needle-shaped plunger, on the end of a screw, exactly fits this seat. As the screw is turned and the plunger retracted, flow between the seat and the plunger is possible; however, until the plunger is completely retracted the fluid flow is significantly impeded. Since it takes many turns of the finethreaded screw to retract the plunger, precise regulation of the flow rate is possible.

Uses

Needle valves are usually used in flow metering applications, especially when a constant, calibrated, low flow rate must be maintained for some time.

Since flow rates are low and many turns of the valve stem are required to completely open or close, needle valves are not used for simple shutoff applications.

Since the orifice is small and the force advantage of the fine-threaded stem is high, needle valves are usually easy to shut off completely, with merely "finger tight" pressure. Small, simple needle valves are often used as bleed valves in hot water heating applications

A pinch valve is a full bore or fully ported type of control valve which presents no obstruction to flow passage. There are a few types of pinch valves based upon application.

Pinch valves used for fluids usually employ a device that directly contacts process tubing. Forcing the tubing together will create a seal that is equivalent to the tubing's permeability.

Major components of a pinch valve consist of body and a sleeve. The sleeve will contain the flow media and isolate it from the environment hence reducing contamination to the environment. Generally used for slurries or processes with entrained solids, because the flexible sleeve allows the valve to close drop tight around solids that would typically be trapped by the seat or stuck in crevices in globe, diaphragm, butterfly, gate, or ball valves. The sleeve material can be selected upon the corrosiveness and abrasiveness of the flow media, a suitable synthetic polymer can be chosen. A pinch valve may be the best type of valve for flow control application if the operation temperature is within the limit of the polymer.

The media controlled by the solenoid valve enters the valve through the inlet port (Part 2 in the illustration above). The media must flow through the orifice (9) before continuing into the outlet port (3). The orifice is closed and opened by the plunger (7).

The valve pictured above is a normally-closed solenoid valve. Normally-closed valves use a spring (8) which presses the plunger tip against the opening of the orifice. The sealing material at the tip of the plunger keeps the media from entering the orifice, until the plunger is lifted up by an electromagnetic field created by the coil.

Solenoid valves are the most frequently used control elements in fluidics. Their tasks are to shut off, release, dose, distribute or mix fluids. They are found in many application areas. Solenoids offer fast and safe switching, high reliability, long service life, good medium compatibility of the materials used, low control power and compact design.

Fluidics (also known as fluidic logic) is the use of a fluid or compressible medium to perform analog or digital operations similar to those performed with electronics.

The use of two-way solenoid valves in central heating systems is not generally recommended due to the high closing speeds, causing water hammering (in the case of direct operated valves), or insufficient pressure drop to operate the pilot system in pilot-operated solenoid valves.

Another use for solenoid valves is in automatic irrigation sprinkler systems.

In the paintball industry, solenoid valves are usually referred to simply as "solenoids." They are commonly used to control a larger valve used to control the propellant (usually compressed air or CO₂).

How to avoid problems

• Ball valves should be transported and stored with the ball in the fully open or fully closed position.
• Flanged ends and welded ends should be protected.
• End protection should be removed only when the valve is installed in the line.
• Valves should be handled using the proper lifting lugs.
• Valves should be stored according to GM storage procedures. Long term storage should be avoided.
• For welded-end valves, advise GM if there will be a post-weld heat treatment (transition pups may be necessary to avoid damages to seals).
• Flush and clean the line before opening/closing the valve.
• Make sure no line-testing fluid is left in the line and/or the valve body.
• Avoid leaving the valve body filled with salt water to prevent internal corrosion.
• During line-testing, valves should be left in the partially open position for the minimum possible amount of time.
• Standard ball valves should be used for on-off service only. Throttling service (use of the valve with the ball partially open) can damage the seats.
• Make sure to take into consideration the actual service conditions when selecting materials for O-rings and seat inserts.
• Always specify anti explosive decompression material for valves to be used in high pressure gas service.
• Make sure the selected actuator has been properly sized (an oversized actuator can be as dangerous as an undersized one).
• Advise GM of cycle frequency to ensure proper sizing of actuator.
• Do not use the actuator to lift the valve.