Valves
Ball Valves
The flow control of a ball valve is a ball with a round hole through it. The ball rotates about an axis that is perpendicular to the hole and to the fluid path. The ball is always in the fluid path. Because the ball valve is symmetrical, either can be the fluid inlet, and thus flow can be from either direction.
The form of control for which ball valves are best suited is starting and stopping flow; however, they can be used for changing flow direction.
Diaphragm Valves
The flow element of a diaphragm valve is a flexible membrane, called a diaphragm that is used to close the fluid path. Because the diaphragm valve is symmetrical, either can be the inlet, and thus flow can be from either direction through the valve.
The form of control for which diaphragm valves are suited is as a stop valve, that is for starting or stopping flow, or regulating flow volume (called throttling)
Gate, Globe & Check Valve
Gate Valves- The flow control element of a gate valve(called a gate, wedge or slide) enters the fluid path from the side and transverses it until the fluid path is completely closed off, stopping the flow. When the valve is open, the gate is entirely cut of the fluid path. Thus flow is in a straight line, with very little resistance from the valve. Because the gate valve is symmetrical, either end can be the inlet, and thus flow can be from either direction through the valve. The form of control for which gate valves are suited is starting and stopping flow.
Globe Valves- The body of a globe valve is configured so that the flow control element ( called a disc) is moved along the axis of the fluid path. The disc is always in the fluid path. The valve opening is annular. The form of control for which globe valves are best suited is regulating flow volume ( called throttling) ; however they can be used as stop valves( for starting and stopping flow).
Check valves- Check valves have different configurations. The most common are the swing check valve, tilting- disc check valve, wafer check valve, lift check valve and stop-check valve. The form of the fluid control of the check valve is the prevention of fluid flow reversal. Check valves are used to isolate separate services connected to a common header to prevent fluid flow from one service to another thereby preventing contamination. Check valves are also used to isolate low- pressure – rated systems and equipment from downstream high – pressure surges.
Butterfly Valves
The butterfly valve is one of a group of valve types commonly called quarter-turn valves. This is because their flow control element moves from the fully open position to the fully closed position with just 90 degrees shaft rotation.
The form of control for which butterfly valves are best suited is regulated flow volume (called throttling); however they can be used as stop valves (for starting and stopping flow).
Plug Valves
The flow element of the plug valve, the plug, is a cylinder or a truncated cone with a hole through it. Because the plug valve is symmetrical, either can be the fluid inlet, and thus flow can be from either direction.
The forms of control for which the plug valve is suited are starting and stopping flow and changing flow direction.
Knife Edge Gate Valves
A style of gate valve different from the standard gate, the knife gate valve is also called a slide valve.The major advantage of the knife gate valve is the ability of its gate to cut through solids that would fill the space between the seat rings in a standard gate valve and prevent closure.
This makes it ideal for use with slurries, solids carried in air, and in dry service such as on storage hoppers. Consequently, knife gate valves are used extensively in process industries such as pulp and paper, waste treatment and mining processing.