Valves

Drain Valve. Image Credit: Pexuniverse Regulator. Image Credit: Beswick Engineering. Solenoid air control valve. Image Credit: Grainger

Valves are mechanical devices that control the flow and pressure of liquids, gases, and slurries within a system. They are also known as regulators and are used in a wide variety of applications. For all types of media that are conveyed through pipes, there must be valves to control their flow. Valves vary greatly in size, design, function, and operation. It is vitally important to select a valve that will provide the most satisfactory performance, valve life, and least amount of maintenance.


Valves Categories

Air Valves (807 suppliers)

Air valves allow metered fluid flow in one or both directions. They are used in pneumatic circuits to regulate the rate of activation or exhaust of cylinders and other pneumatic devices.


Backflow Preventers (126 suppliers)

Backflow preventers are assemblies consisting of two check valves and two shut off valves. These assemblies may also include test cocks for each chamber.


Ball Valves (2,069 suppliers)

Ball valves provide tight shut-off and characterizable control. They have high rangeability due to the design of the regulating element and few complications from side loads typical of butterfly or globe valves.


Butterfly Valves (1,229 suppliers)

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. They are normally used as throttling valves to control flow.


Check Valves (1,941 suppliers)

Check valves are self-activating safety valves that permit gases and liquids to flow in only one direction, preventing process flow from reversing. They are classified as one-way directional valves. 


Compressor Valves (16 suppliers)

Compressor valves are valves used within a compressor to allow gas flow to and from the cylinder area.


Control Valves (1,710 suppliers)

Control valves or proportional valves are power-operated devices used to modify fluid flow or pressure rate in a process system.


Diaphragm Valves (417 suppliers)

Diaphragm valves close by means of a flexible diaphragm attached to a compressor.


Dispensing Valves (183 suppliers)

Manual or automatic devices for the accurate dispensation of fluid or granular materials.


Diverter Valves (274 suppliers)

Diverter valves direct flow from one inlet to one of two or more outlets.


Drain Valves (175 suppliers)

Drain valves are designed to automatically remove liquids from process lines as necessary.


Fire Sprinkler Heads (94 suppliers)

Fire sprinkler heads deliver a high-pressure flow of water or dry chemicals to a fire. They are usually are heat-activated and part of a larger fire prevention and safety system.


Gas Valves (520 suppliers)

Gas valves are used to handle and control the flow of gaseous media such as liquefied petroleum and natural gas. They are made of metal or plastic and vary in terms of valve size, pressure rating, number of ports, and flow.


Gate Valves (1,164 suppliers)

Gate valves and knife valves are linear motion valves in which a flat closure element slides into the media stream to shut off flow.


Globe Valves (772 suppliers)

Globe valves are linear motion valves with rounded bodies, from which their name is derived.  They are widely used in industry to regulate fluid flow in both on/off and throttling service. 


Hydraulic Valves (696 suppliers)

Hydraulic valves contain and transfer the flow and pressure of hydraulic fluid in hydraulic power systems. They range from simple shutoff valves to precision control valves.


Industrial Valves (3,319 suppliers)

Industrial valves are classified in many different ways. They can be distinguished by material of construction, media handled, and/or application.


Insertion and tapping valves are used to isolate media within the existing line while an additional connection is made.


Mixing Valves (196 suppliers)

Mixing valves combine the flow of two or more inlets into a single outlet for applications such as temperature and concentration control.


Needle Valves (561 suppliers)

Needle valves are small valves used for flow control in liquid or gas services. The fine threading of the stem and the large seat area allow for precise resistance to flow.


Pinch Valves (160 suppliers)

Pinch valves include any valve with a flexible elastomer body that can be pinched closed, cutting off flow, using a mechanism or fluid pressure.


Plastic Valves (342 suppliers)

Plastic valves are made from plastic materials and are used in applications that require corrosion resistance and/or chemical handling.


Plug Valves (456 suppliers)

Quarter-turn plug valves use a cylindrical or tapered plug with a hole in the center to control straight through flow when in the open position.


Pressure Relief Valves (989 suppliers)

Pressure relief valves are self-actuated safety valves designed to relieve excess pressure upstream from the line.


Sanitary Valves (208 suppliers)

Sanitary valves are designed for applications requiring clean or sterile processing. 


Servo Valves (90 suppliers)

Servo valves provide closed loop flow or pressure response to an electrical or electronic control signal. They are used in air, gas, and liquid applications.


Solenoid Valves (988 suppliers)

Solenoid valves are devices that use a solenoid to control valve activation.


Solids Feeders (541 suppliers)

Solids feeders are used to deliver powder, granular and other bulk solid materials along a process line, or to and from process units, storage bins, conveyors and product packaging.


Solids Valves (196 suppliers)

Solids valves are used to control or regulate the flow of powder, granular and other bulk solid materials along a process line, or to and from process units, storage bins, conveyors and product packaging.


Steam Valves (255 suppliers)

Steam valves are used to control the flow and pressure level of steam and heated water vapor.


Tempering valves and thermally actuated valves contain a thermal sensing component that opens or closes in response to temperature changes.


Water Control Gates (51 suppliers)

Water control gates are used to control the mass flow of water or wastewater in various environmental and process applications.


Water Valves (580 suppliers)

Water valves are designed to handle and control hot water, cold water, ground water, potable water, salt water and/or wastewater. They are made from metal or plastic.



Valve Construction

Although there are many different types of valves and many are designed for specific applications, there are several valve components that are uniform throughout all valves. When selecting a valve it is also important to consider the fitting and material that will needed for the system.


Valve components


Basic parts of a valve.
Image Credit: RoyMech

Valves can vary greatly in size and design but there are several basic components to valve functionality.

The body of the valve holds the parts together. The ends are designed to connect into the pipe or equipment in the system and generally are butt or socket welded, threaded or flanged. The body is the first pressure boundary to come into contact with the surrounding environment and system media. The environment is an important consideration when selecting the body material.

The bonnet is the cover for the opening in the body. This is the second most important boundary of a pressure valve and is made from the same material as the body. The bonnet can also support internal valve parts, such as the stem, disk, and actuator.

Trim is a term used for the replaceable internal parts such as the disk, seat, stem, and sleeves used to guide the stem. The trim is responsible for the basic motions and flow control features of the valve.

The disk and seat provide the capability for permitting and prohibiting fluid flow. The system is under full pressure when the disk is closed. The seat provides a surface for the disk to seal to in order to stop the flow. The valves may have one or more seats depending on the type. For example, a gate valve has two seats; one on the upstream side and the other on the downstream side. The design of the disk is generally where valves get their name.

The stem is responsible for the movement of the disk, plug or the ball for opening or closing the valve. It is usually forged and connected to the valve hand-wheel, actuator, or the lever by threading. The stem moves the disc in a linear or rotary movement to open or close the valve.

  • There are five types of valve systems depending on the application.

    • Rising stem with outside screw and yoke - The exterior of the stem is threaded, while the portion of the stem in the valve is smooth. The stem threads are separate from the flow medium by the stem packing. This type of valve is common for larger valves.
    • Rising stem with inside screw - The threaded part of the stem is inside the valve body, and is in contact with the flow medium. When rotated, the stem and the hand-wheel rise together to open the valve.
    • Non-rising stem with inside screw - The valve disc travels along the stem, like a nut as the stem is rotated. Stem threads are exposed to the flow medium so this model is appropriate when space is limited to allow linear movement, and the flow medium does not cause erosion, corrosion or abrasion of the stem material.
    • Sliding stem - The valve stem slides in and out of the valve to open or close the valve. This design is for hand-operated, rapid opening valves, and control valves that operate by hydraulic or pneumatic cylinders.
    • Rotary stem - This is a commonly used model in ball, plug, and butterfly valves. A quarter-turn motion of the stem opens or closes the valve.

Stem packing is used to form a tight seal between the stem and the bonnet. The packing is fitted with one of several components: a gland follower, a gland, stuffing box, packing material, or a backseat. Packing is important in preventing damage to the stem and fluid or gas loss. It is commonly a fibrous material or compound (such as Teflon®) that forms a seal between the internal and the outside parts of a valve.

The yoke and yoke nut are used to connect the body with the actuating mechanism. The yoke must be strong enough to withstand the forces, movements, and torque developed by the actuator. The nut is used to control the movement of the stem.

Valve Fittings

Threaded
Compression
Fitting
Bolt Flange
Clamp Flange
Union
Tube Fitting
Butt Weld
Socket Weld /
Solder


Valve Actuator

The valve actuator operates the stem and disk to open and close the valve. There are several types of actuators to consider depending on the needs of the system such as the torque necessary to operate the valve, speed and the need for automatic actuation.

To select the correct valve actuator, visit GlobalSpec’s How to Select Valve Actuators.

Material of Construction

Valves are made of a wide variety of materials including metallic and nonmetallic options. When selecting a material, the operating environment (i.e. ambient heat), lifespan (i.e. maintenance), and media (i.e. gas or corrosive liquid) should be considered. The most common material is carbon steel because it does very well in high heat, is easily available, and is inexpensive, but it is not suited for corrosive materials. Stainless steel is strong and exhibits resistance to both corrosion and high temperatures, but costs more than carbon steel. Special alloys are used for severe applications such as high pressure or extremely corrosive materials.

Selection Tip: Will the valve be mostly open or mostly closed? Some materials show different characteristics in stagnant verses continuous-flow conditions.

Performance Specifications

Flow

A valve can be used to stop and start as well as throttle or regulate the flow or movement of media through a system. The given and desired properties of the flow can be used when selecting a valve. For a full break down of performance specifications and calculations, visit GlobalSpec’s Valve Flow page.

For information on monitoring and maintaining flow rate variables, visit GlobalSpec’s How to Select Flow Controllers.

Valve Sizing

The science behind valve sizing is determining the flow through the diameter of the valve. Correct valve sizing is important for throttling valves as well as for open/close valves. More information on determining the best valve size is available on GlobalSpec’s Valve Size page.

Installation

Before installation, valves should be stored in a safe, clean, dry place to prevent contaminates from getting into the moving parts and damages to the body of the valve. The inside of the valve should be blown or flushed out to remove all dirt and grit from manufacturing, packaging, and storage.

Cost

Open/close - Some of these valves are considered to be a onetime purchase; use until they break and then discard them

Throttle - Throttle valves have a number of cost factors, not including the initial cost and true installed cost.

The true installed cost over time includes the purchase price, installation and start up, training, maintenance, and cost of spare parts. The reliability of the valves can also affect the cost because the more reliable valves will not need as much maintenance.

Once installed, GlobalSpec’s Valve Repair page can be consulted to find valve repair specialists.


Other Information

Standards

See GlobalSpec’s Valve Standards page for a full list of valve standards and regulations.


Applications

See GlobalSpec’s Valve Application page for more information.


Terminology

See GlobalSpec’s Valve Terminology page for more information.


Symbols

See GlobalSpec’s Valve Symbols pages for more information.