Here are brief descriptions of the most common types of flow control valves used in the industry today.
Multi-Turn Valves, or Linear Motion Valves
A general service valve, primarily used for non-throttling on-off service. A vertical gate, or disc, closes the valve by sliding down through the valve and blocking the flow.
This design is used for on-off service and throttling applications. The valve is closed by lowering a flat or convex-bottomed plug onto a horizontal seat mounted centrally in the valve.
This valve is sealed using flexible elements, such as rubber tubing, that are pinched to shut off the flow of liquid. It is suited to slurries or liquids that contain a lot of suspended solids.
Suited to handling dirty, corrosive and erosive substances, this valve is closed by a compressor attached to a flexible diaphragm. When lowered by the valve stem, the diaphragm forms a seal to cut off flow.
This valve is fitted in small lines to restrict flow and control volume. Fluid passing through the valve turns 90 degrees and passes through a rod with a cone shaped tip. The tip is moved about the valve seat to alter the size of the opening and control the flow volume.
Many control valve manufacturers produce custom designed valves and actuators, in a wide range of sizes and materials, for specific applications. Each design has its advantages, and it is critical to select the correct valve, taking into account factors including the following.
– The nature of the substance
– The required flow rate
– Requirements for flow control and shutoff
– Working conditions and extremes of temperature and pressure
– Resistance to corrosion, erosion and other forms of attack
– Maintenance and repair requirements
– Any requirements for valve actuators.
Quarter Turn Valves, or Rotary Valves
This valve can be closed or opened by a quarter turn in either direction. This aligns the flow path with a hole in the center of the cylindrical or tapered plug and permits flow. Its primary use is on-off service, or in some throttling functions.
This works in similar applications to the plug valve, using a rotating ball with a hole through it that allows flow in the open position, or blocks flow when rotated by 90 degrees.
This is another design of pivoting valve inside a pipe. It features a circular disc, or vane, that pivots at right angles to the flow direction to control or shut off the flow. It has applications in throttling and on-off services.
This valve checks, or prevents, backflow. Fluid flow in the correct direction causes the valve to open, while any backflow forces it to close.
Pressure Relief Valve
This is a protective valve that opens to release pressure when it exceeds a certain level in steam, gas, liquid or air line. It is designed to protect the system from over-pressure, and will automatically close when pressure returns to a preset safe level.
A control valve is designed to vary flow rate automatically, based on signals it receives from sensors. It achieves precise and accurate proportional flow control. There are purpose-build control valves, or most other types of valves can be upgraded to control valves by adding devices such as positioners and power actuators to control the linear or rotary movement of the valve.