Valves

Ball Valve
A ball valve (like the butterfly valve, one of a family of valves called quarter turn valves) 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 position lets you "see" the valve's position.

There are three general types of ball valves: full port, standard port, and reduced port.

• A full port ball valve has an oversized ball so that the hole in the ball is the same size as the pipeline resulting in lower friction loss. Flow is unrestricted.
• A standard port ball valve is usually less expensive, but has a smaller ball and a correspondingly smaller port. Flow through this valve is one pipe size smaller than the valve's pipe size resulting in slightly restricted flow.
• In reduced port ball valves, flow through the valve is two pipe sizes smaller than the valve's pipe size resulting in restricted flow.
• A "trunnion" ball valve has a mechanical means of anchoring the ball at the top and the bottom.

Gate valve
A gate valve is a valve that opens by lifting a round or rectangular gate 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.

All gate valves have 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 leakproof 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.

Globe Valve
Globe valves are named for their spherical body shape. The two halves of the valve body are separated by a baffle with a disc in the center. Globe valves operate by screw action of the handwheel.
A bonnet provides leakproof closure for the valve body. Globe valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest bonnet, offering a durable, pressure-tight seal. Union bonnet is suitable for applications requiring frequent inspection or cleaning. It also gives the body added strength. Bolted bonnet is used for larger or higher pressure applications.

Butterfly Valve
A Butterfly valve is a type of flow control device, used to make a fluid start or stop 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 a handle on the outside of the valve. Rotating the handle turns the plate either parallel or perpendicular to the flow of water, shutting off the flow.

There are three types of butterfly valve:

1. Resilient butterfly valve which has a flexible rubber seat. Working pressure up to 1.6 Mpa
2. High performance butterfly valve which is usually double eccentric in design . Working pressure up to 5.0 Mpa
3. Tricentric butterfly valve which is usually with metal seated design. Working pressure up to 10.0 Mpa

Check valve
A check valve is a mechanical device, a valve, that normally allows fluid or gas to flow through it in only one direction. An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.

Solenoid Valve
A solenoid valve is an electromechanical valve (for use with liquid or gas) controlled by running (or stopping) an electrical current through a solenoid, (which is a coil of wire) thus changing the state of the valve. Solenoid valves may have two or more ports: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports.
Solenoid valves may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control. Multiple solenoid valves can be placed together on a manifold. A spring may be used to hold the valve opened or closed while the valve is not activated.

Relief Valve
The relief valve is a type of valve used to control or limit the pressure in a system by allowing the pressure source fluid to flow from an auxiliary passage, away from the main flow path. The relief valve is designed or set to open at a predetermined pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits. When the pressure setting is exceeded, the relief valve becomes the "path of least resistance" as the valve is forced open and a portion of the fluid is diverted through the auxiliary route. The diverted fluid (liquid, gas or liquid-gas mixture) is usually routed through a piping system known as a flare header to a central, elevated gas flare where it is burned and the resulting combustion gases are released to the atmosphere.

In the petroleum refining, petrochemical and chemical manufacturing, natural gas processing and power generation industries, the term relief valve is synonomous with the terms pressure relief valve (PRV), pressure safety valve (PSV) and safety valve. In most countries, such industries are legally required to protect pressure vessels and other equipment by using relief valves. Also in most countries, equipment design codes such as those provided by the ASME, API and other organizations must be complied with and those codes include design standards for relief valves.

Actuation