Fundamentals of Valve Design: Types, Sizes, and Common Errors
Valve design refers to creating and defining a valve’s specifications that can perform specific functions within a fluid handling system. It involves determining the size, shape, materials, and operating parameters of the valve that would best meet the requirements of the system and the intended application.
Valves are carefully-designed components that regulate or control fluid or the direction it flows using numerous kinds of opening, closing, or partially cutting-off apertures. They control the pressure and flow of fluid within a system.
Valve design varies from different materials and is available in different types. Since they are vital for plant operation, they function within piping systems as any of the following:
- Multi-port valves (divert flow)
- Regulating valves (regulate or control flow)
- On-Off valves (start and stop the fluid flow)
- Check valves (prevent backflow of fluid)
- Pressure-vacuum relief valves or pressure relief valves (relieve pressure from a piping system)
This shows the various valves that control or regulate fluid flow rate in a piping system or a reciprocating compressor.
Types of Valve Design
As highlighted in the previous section, different valves are designed for specific purposes, and valve design plays a crucial role in this. Below is a list of the most commonly used valve types in the piping industry:
- Gate valves
- Ball valves
- Check valves
- Needle valves
- Butterfly valves
- Plug valves
- Diaphragm valves
- Globe valves
- Pinch valves
- Pressure relief valves
Let’s take a brief look at each of these valve types.
Gate valves are a commonly used type in many process plants and play a critical role in valve design. The fluid flow is controlled by linear motion, and they are either fully closed or fully open. These valves are used in various fluid services, including fuel gas, lube oil, feedwater, hydrocarbon, and more, making them versatile in valve design.
Gate valves provide excellent shut-off when in operation. However, they cannot be used as a control or regulating valve since the apertures are opened or closed slowly when opening them.
There are four distinct types of gate valves:
- Flexible wedge gate
- Solid wedge gate
- Parallel disks or split wedge gate
- Rising Stem or OS & Y gate valves
These will be discussed in other articles.
Ball valves, shaped like balls, are rotary turn quarter valves. They are quick-acting valves that can be turned off at 90 or zero degrees.
The ball spigot is smaller and lighter in rating compared to gate valves. They can be controlled clockwise or anticlockwise through the plunger.
Check valves are used primarily in preventing backflow within a piping system. They only allow the flow to pass in only one direction.
Whenever back pressure is created within a system, the check spigot shuts off automatically and prevents fluid flow. In addition, check valves are capable of intercepting and checking the flow of reversal.
The three common types of check valves used in piping systems are:
- Lift check valves
- Piston check valves
- Swing check valves
These will be discussed in other articles.
Needle valves share a slight similarity with globe valves. However, the most significant difference between these two valves is that the needle valve looks like a needle, hence the name.
Needle valves are required in instruments that call for an ultra-accurate flow of fluid. It is usually employed in a small-diameter pipe and finds much use in very low-pressure control applications.
Needle valves are commonly used in nearly every industry for many applications, including metering or control of gas, steam, oil, and non-viscous liquids.
Butterfly valves are quarter-turn rotary motion valves that help in regulating start-stop flows. The most significant benefit of this valve type is that it has a thin body, which takes up a very small space within piping systems. This is why butterfly valves are used extensively in various applications.
Butterfly valves are lightweight and compact, capable of moving like a butterfly within a closed space.
Plug valves are quarter-turn rotary valves in which the disc rotates in a circular motion. They are called plug valves because the disc takes up the shape of the plug, and it also has a passage.
Leakages from plug valves are negligible. This is why they are used in vacuum and high-pressure services.
Globe valves are used for regulating fluid and start-stop functions. A globe stopper kicks into action at a particular place within the system where controlling fluid flow is necessary while considering the system’s tightness and leakage.
Globe valves are much more expensive than their counterparts, i.e., gate valves. However, the additional expense is worth it since they offer excellent tightness and are more leakproof than gate valves. In addition, globe valves can be used as control valves.
Globe valves are also used in transporting lube oil and fuel oil. Their spherical shape at the bottom is one of the reasons for their name.
The three distinct types of globe valves are:
- Angle types globe valves
- Y types globe valves
- Z types globe valves
They will be discussed in other articles.
Pinch valves come with a single pinch tube and simple mechanisms. The pinch tubes are made of Normally rubber.
The most significant benefit of pinch valves is that they can be used in solid particles with lots of slurries.
Pressure Relief Valves
Pressure relief valves release pressure when an overpressure occurs within the pressure relief equipment or piping system. The vacuum created within this system is getting eliminated, thanks to vacuum valves that swing into action to protect the piping system.
In other words, this considerable pressure relief secures the entire piping system.
Valve Design Classification
Valves can be classified based primarily on the movement of the closure element. Here are the categories they are classified in:
The closure member – i.e., parallel gate or wedge gate – of this valve type moves at right angles to the flow direction at the valve port. Gate valves, plug valves, ball valves, and butterfly valves fall into this category.
In this type of valve, the closure member – i.e., plug or disc – moves along the seat axis away from or towards the direction of the port or valve seat. Globe valves, piston valves, and needle valves are in this category.
The closure member of this type of valve is a flexible passage that is pinched or flattened to restrict the flow and vice versa to let fluid pass through the valve. For example, pinch valves fall into this category.
The closure member of this type of valve has a port that is turned 90 degrees so that it aligns perfectly with the direction of fluid flow. This allows full flow across the valve.
The port can also be at right angles to the direction of fluid flow, effectively shutting off the fluid flow.
By understanding the most commonly used valve types in piping systems, identifying and repairing issues in your compressor or piping system can be easier. This highlights the importance of being knowledgeable in valve design.
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