Check valves are a simple and straightforward way to provide engineers and installation teams alike with a relatively inexpensive and reliable method of preventing the backflow of a liquid or gas in a variety of applications. Often found in petrochemical, oil and gas applications; check valves are a great way to prevent corrosive fluids and gases from flowing backwards in an application.
However, this versatile valve doesn’t just stop there! Suitable for both domestic and industrial applications, from process water control to drinking water systems, the check valve is a great way to secure the directional flow of your water or gas. Read on to find out more about the array of check valves available and how you should select the most appropriate one for your application.
What is a check valve?
Generally speaking, a check valve is installed into a pipeline to prevent back flow of gases and liquids. This means that a check valve is essentially a one-way valve, through which the flow can run freely one way, but not the other. This is because if the flow turns in a check valve, the valve itself will close in order to protect the piping, other valves, the pump or other instrumentation that is part of this solution.
However, if the flow turns and no check valve is in place, a water hammer can occur which can in turn cause costly damages to pipelines or components due to the extreme force with which the water hammer takes place.
What is water hammer?
In a pumped system, water is often forced from a lower level up to a higher level by using a pump. This means that the liquid will only flow in one direction when the pump is in operation, however, when the pump is stopped the flow of the fluid will reduce until that also stops. One working example of this is the use of a pump to extract crude oil from deep beneath the ocean flow on a North Sea oil rig. As the crude oil is pumped upwards towards the rig to be extracted and utilised in oil applications, we do not want to lose any of this oil by it flowing back down the pipeline. This is where a check valve comes in as this prevents the crude oil from returning back down the pipe.
Most of the time, the rate at which the liquid reverses back down the pipeline is not a cause for concern, which is why standard check valves do often perform well. However, in some pumped systems with fast flow reversal, it is crucial that a check valve that can stand up to the challenge is selected. This is because, if the pump stops and the forward flowing fluid reverses back down the pipeline before the check valve has fully closed, the flow of the fluid will force the valve door to slam onto its seat. This will instantaneously stop the reverse flow of the liquid, whilst also in turn stretching the pipe which can cause costly damage and lead to expensive breakdowns. This damage is caused by the surge in pressure which can lead to cracked pipes or bust pipes due to vacuum pressure being formed.
How to prevent water hammer
To prevent the occurrence of a check valve slamming and therefore causing a water hammer, the valve should close one of two ways. If a valve is set to close very quickly, this will prevent the onset of reverse flow. If the valve is set to close slowly, it will require additional equipment to make this possible. These additional kits include hydraulic dampers to cushion the valve closed.
Additionally, slower closure does allow fluid to pass through the check valve until it closes, which means that consideration must be given to the upstream pump to ensure that it is suitable for the reverse flow of liquids in a check valve application.
Where are check valves used?
Check valves are suitable for use in an array of applications, with one such example being that they are often placed on the outlet side of a pump. This is done to prevent a pump from back flow, whilst centrifugal pumps are not self-priming and therefore check valves are essential to keep water in the pipes and prevent the costly ramifications of water hammer.
Check valves are often also used in HVAC systems. HVAC systems are heating, ventilating and air conditioning systems. These systems are often used in large buildings where a coolant needs to be pumped to a level that is a number of stories high. Here, check valves are used to make sure that these coolants and other fluids are unable to flush back down the pipeline.
What are the different types of check valves
There are a range of different check valves available on the market, all of which are designed to suit an array of applications. These include:
Non-return check valves – These valves allow the flow of media in a single direction only and are often the most cost-effective check valve on the market. In addition, non-return check valves are available in a wide range of sizes and materials to ensure that they can act under pressure in a variety of liquid and gas applications.
Water check valves – High-performance water check valves are up to the challenge of handling liquids and adhering to an array of process environments and their requirements.
Gas check valves – Often manufactured from durable stainless steel, gas check valves are compatible with all semiconductor gas applications and processes, including those with corrosive media.
Selecting the correct check valve
Selecting the most suitable check valve for your application can be tricky. With valve solutions from industry leading brands such as Parker, there are plenty of options available to you. To keep your application running smoothly, it is important to select the most appropriate solution for your problem. Choose between water check valves, gas check valves and non-return check valves to find the most suitable solution.