What are Non-Return Valves? A Guide

Despite their very simple function, non-return valves have become an invaluable, if often overlooked, component in pipelines and systems across the globe. But what are non-return valves, and why are they so useful?

In this article, we will detail everything you need to know about non-return valves. Keep reading to learn more…

What is a non-return valve?

Non-return valves are a vital component of a single direction fluid system. These valves, sometimes referred to as reflux valves, retention valves, foot valves, one-way valves, check valves, or simply NRV, are designed to prevent backflow – which otherwise might damage or contaminate equipment.

Non-return valves are a common valve used in many applications, from household plumbing systems, to large-scale industrial equipment.

While non-return valves may come in different designs, the key components remain the same: 

• The valve body is the main structure, which houses the internal components.
• The internal mechanism, usually made up of a disc, ball, or hinge and flap, allows and blocks the flow depending on the direction.
• The seal connects to the internal mechanism, and prevents leaking when the valve is in the closed position.

The simple, yet effective mechanism operates based on the principle of differential pressure. When fluid flows in the intended direction, the valve is pushed open to allow it to pass through. If the flow of the fluid reverses direction, the change in pressure causes the valve to close, blocking the attempt.

What are the different types of non-return valves?

As the function of a non-return valve is highly effective, the design has seen multiple variations to suit different applications and requirements. Understanding the function of non-return valves is crucial for ensuring you select the right valve for a specific application. Below, we’ve explored some of the more common types of non-return valve.

Ball check valves

Ball check valves use a ball trapped within a chamber to allow or prevent the flow. Usually made of rubber or metal, the ball rolls away from the valve seat when the flow is moving in the intended direction, and rolls back onto the seat when the flow reverses.

These valves are a simple, robust solution, and are commonly found in systems such as water treatment, chemical processing, and oil and gas industries.

Swing check valves

Swing check valves feature a disc attached to a hinge or pivot. As the flow moves through in the intended direction, the disc swings away from the seat, opening like a door to welcome through the flow. If the flow changes direction, it puts pressure on the rear of the disc, which swings it back into place on the seat – effectively closing the door.

The design of the swing check valve works best when in a pipeline with a horizontal flow, and is therefore best suited for water supply systems, HVAC systems, and applications where a low-pressure drop is desired.

Lift check valves

Similarly to swing check valves, lift check valves contain a disc. However, instead of swinging open, these discs lift off the seat to permit the flow of liquid, and will close automatically when the liquid stops, or changes direction.

As lift check valves are typically installed in horizontal or vertical pipes, they are commonly used in steam, gas, and high-pressure systems, where a compact design and reliable sealing are essential.

Spring valves

When a fast response is necessary, a spring valve is an excellent solution. These valves incorporate a spring into the internal mechanism to assist in the closing of the valve. The pressure of the spring can be adjusted to suit the various application requirements.

Spring valves are commonly found in fuel and hydraulic systems, or high-pressure applications where a fast response is required.

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Non-slam check valves

Also known as silent check valves, non-slam check valves are designed to close gradually, reducing the risk of an immediate blockage occurring. In order to slow the process of closing, they typically feature a spring-loaded mechanism to return the ball or disc slowly.

Non-slam check valves are ideal for pumping systems, irrigation, or water treatment systems where a sudden stop in flow may cause damage.

Double check valves

For systems that require added security and reliability, we have the double check valve. These valves contain two internal mechanisms, which act as a failsafe for one another to ensure that a potential backflow is prevented.

Double check valves have found wide appeal in fire prevention, lawn irrigation, and potable (human-safe) water systems, where backflow prevention is critical.

Low-pressure non-return valves

In situations where the pressure of a flow is too low to effectively open a valve, a low-pressure non-return valve is required. These valves are designed to open with even the minimal amount of forward pressure, without compromising the process of blocking a reversed flow.

Low-pressure non-return valves are usually found in applications such as air compressors, vacuum systems, or gas lines.

What are non-return valves made of?

There are three main materials that non-return valves are commonly made from:

Brass

Brass non-return valves are a great choice for low-pressure applications, but are not a good fit for purified water, chlorinated water, or seawater, as brass fittings can lose zinc when submerged in water. This weakens the metal, and can make it porous.

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Stainless steel

Non-return valves made from stainless steel are regarded for their extreme robustness, and ability to withstand both high and low temperatures. However, this resilience comes at a higher cost than brass or plastic models.

PVC

Polyvinyl chloride (PVC) non-return pipes offer an excellent level of resistance to corrosive substances, such as acid, seawater, or solvents. However, as they are more susceptible to heat, and can degrade in hotter temperatures.

What are non-return valves used for?

Non-return valves have become an essential component in the operation of many industries, where a backflow can cause damage, contamination, or pressure loss to a system. Below, we’ve explored some of the most common applications…

Gas and oil industries 

Non-return valves play a critical role in maintaining pipelines and equipment. By ensuring a unidirectional flow, they are able to protect pumps, compressors and other sensitive components from damage by preventing the backflow of crude oil, natural gas, and other fluids.

Ensuring a consistent, one-directional flow helps to maintain steady pressure, and reduce the risk of leaks and spills, which could be hazardous to the environment, and costly to rectify.

Water treatment

Contamination is a serious concern in water treatment and distribution plants. Implementing non-return valves that ensure the water flows in the intended direction prevents backflow, which can spread bacteria into parts of the system that are required to stay clean.

Non-return valves are used in the distribution of water for households and businesses alike, and are vital for various stages of water treatment, such as filtration, disinfection, and distribution. Non-return valves protect public health by ensuring a reliable supply of clean water.

HVAC systems

Heating, ventilation, and air conditioning systems (HVAC) require non-return valves to maintain proper airflow. They maintain pressure within the system, preventing the backflow of gases or liquids. 

They find common application in air ducts, air handlers, heat exchangers, and many other HVAC components.

Manufacturing and industrial applications

Non-return valves have seen widespread use in the manufacturing and industrial industries thanks to their ability to protect equipment, and increase safety. 

By preventing backflow in fluid transfer systems, such as hydraulic circuits and pneumatic systems, they maintain a consistent pressure, and prevent equipment damage that would be caused by a reverse flow.

Plumbing systems

Non-return valves have found use in plumbing systems, from household to industrial level. Preventing the backflow of water and waste protects the integrity of the plumbing system, and ensures the safety of drinking water.

They are found in most situations where contamination is a risk, such as irrigation systems, water heaters, and sewage disposal systems.

Fire protection

Non-return valves play an essential role in fire protection systems such as sprinklers and fire hydrants. By ensuring water flows in the intended direction and maintaining the pressure needed for effective firefighting, they are able to ensure that fire protection systems are ready to work in an emergency.

Chemical processing

Maintaining the effective control of aggressive and corrosive chemicals is a vital consideration in chemical processing plants. Non-return valves prevent the backflow of hazardous substances, protecting equipment and personnel from harm. 

These valves are designed to withstand the harsh conditions of being subjected to chemical processing environments, to ensure safety and reliable performance.

Agriculture

Agricultural and irrigation systems require non-return valves to control the flow of water and nutrients to crops. 

Preventing backflow in these systems ensures an even and efficient distribution of fertiliser across the crops, which is required for the healthy growth of the plant life, and contributes to the efficient, sustainable agricultural practice.

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What are the benefits of using non-return valves?

As we’ve previously discussed, the ingenious design of the non-return valve has seen it achieve widespread use all over the world across a myriad of businesses and industries. As the design ensures that the flow of liquid or gas travels only in one direction, there are a number of benefits to using these in your work, which we will explore in more detail below.

Reducing risk of contamination

By controlling the flow of a gas or liquid, the non-return valve is able to reduce the risk of contamination to a system. This is particularly true in systems where different fluids or gases must be kept separate, such as chemical processing or pharmaceutical manufacturing.

Ensuring a unilateral flow direction prevents backflow from transporting bacteria or harmful substances to other parts of your machinery – protecting the system (and often, the fluids within).

Minimising risk of pressure loss

If the flow of a pipeline changed at random, the system it connects to could suffer a loss of pressure. Non-return valves are designed to minimise this risk, in turn maintaining system efficiency – and protecting your system from pressure-loss related damages.

This benefit has seen non-return valves used frequently in HVAC and hydraulic systems, where pressure consistency is crucial. 

Improving safety

Unexpected backflow can cause massive damage to systems that require a consistent, unidirectional flow. This damage can cause pressure surges, equipment failure, or even risk to human life.

Non-return valves can mitigate these risks, protecting both the equipment and personnel operating it.

Reliability and efficiency

Maintaining a consistent, one-directional flow helps systems to remain stable and operate at maximum efficiency. This reliability is not only important for critical systems, such as fire protection applications, but for protecting an operation as a whole.

Drops in stability can cause the need for frequent maintenance and replacements, which can be very costly for a business. Non-return valves can ensure this stability, which in turn improves the cost-effectiveness of an operation, and extends the lifespan of the system itself. 

Simplicity

The simplistic design of non-return valves allows them to work reliably, as there are fewer parts to malfunction or break over time. This reduces the need for monitoring, or making adjustments, which makes them a practical and dependable solution.

How to install a non-return valve

Correct installation is crucial for a non-return valve to work properly, so it’s important to get it right. Here are some bits of advice on how to properly install a non-return valve:

Selecting the correct valve

To find the correct valve for your application, consider factors such as the type of fluid or gas that will pass through, the level of pressure you expect, both the internal and external temperatures, and also the flow rate.

It is also important to ensure that you select the correct size of your valve. Non-return valves are usually installed in a pipeline at “line size”. For example, a 50mm valve is installed on a 50mm pipe. 

It is vital that you select the correct size valve. An oversized valve will not open fully, and will clatter, causing the seat and spring to wear out at a quicker rate, and resulting in broken parts. Similarly, an undersized valve will result in a high-pressure drop, which can constrict the flow, and waste energy.

Lastly, remember that some types of valves can only be installed horizontally, or vertically. If your pipe can only support one of these, make sure that you use a valve that will work with that alignment. 

Consider placement

There will likely come a time when you need to inspect or replace your non-return valve. As such, you should think about where you install it. Placing a non-return valve somewhere that allows for easy access for maintenance and inspection will make your life a lot easier in the future.

We recommend avoiding placing the valve near bends or other fittings in the pipeline, as these may cause issues that can affect the valve’s performance.

You should also notice that the non-return valve has a small directional arrow somewhere on the body of it. This is known as the flow direction arrow, and informs you which way the valve should be positioned to allow for the intended flow to pass through. Always make sure you properly fit the valve according to the flow direction arrow, or you may damage your system and need to make costly repairs – and refit the valve again.

Connect securely

A non-return valve needs to be securely fitted to ensure that it works properly and does not leak. To prevent issues, make sure that you use the appropriate fittings when connecting the valve, and tighten them thoroughly and uniformly to avoid any misalignment (which otherwise may lead to leaks or valve failure).

You should also ensure that the piping on either side of the valve is supported to prevent stress to both the valve connections, and the body. This will help to improve the longevity of your system, saving time and money in the long term.

How to maintain a non-return valve

Maintenance of a valve is good practice to ensure that you spot any issues or concerns before they become problems. We’ve included some of our best practice advice below…

Inspect regularly

Build routine inspections of your non-return valve into the scheduled maintenance of your pipeline. This will give you the opportunity to check for signs of wear, corrosion, or other damage.

Switch off the pipeline, uncouple the valve, and check inside to ensure there is no debris or build-up affecting the internal components that may affect performance.

Clean and lubricate

During your inspections, separate the non-return valve from the pipeline and clean it thoroughly. Over time, debris or sediment may build up inside the valve, which will impact its performance, and may lead to backflow.

Use appropriate cleaning products that are compatible with the valve to remove any build-up. Where necessary, lubricate the moving parts, such as the hinge, to ensure it functions properly. 

Top tip: the valve manufacturer should be able to list any cleaning agents or lubricants that are recommended for use with your non-return valve.

Test and monitor

Running periodic tests of your valve will ensure that it is working properly. This may involve checking the non-return valve’s response to intended flow and backflow, ensuring that it closes completely when the latter is apparent.

During these tests, monitor the system’s pressure levels. Sudden changes may indicate issues inside the valve or system that would need to be addressed.

Replace damaged or worn parts

Over time, the components of a non-return valve may start to show signs of wear, or get damaged. During your inspections, check each part of the valve, and test thoroughly. If in doubt of the valve’s performance, replace the affected parts.

Top tip: we recommend keeping spares on hand, especially for critical systems that require minimal downtime.

Common issues with non-return valves

Like all valves, non-returns are susceptible to wear and damage over time. If you are in doubt of the performance of your valve, here are some common issues that you can check for:

Leakage

If your non-return valve has sprung a leak, check for worn or damaged areas and replace them. Ensure that the valve is seated correctly, and that there are no bits of debris or other obstructions that may prevent a tight seal.

Noise

If the non-return valve has started making an unusual noise, such as a hammering or chattering, this may indicate that either the valve was incorrectly installed, or contains a blockage.

With the pipeline shut off, disconnect the valve and give it a proper inspection, cleaning and lubricating where necessary. Once you are assured that the valve is free of obstructions, reconnect it, ensuring that the alignment and fittings are correct and sealed tight.

Low pressure

If you notice a loss of pressure, or a reduced flow, it may be that there is a blockage or build-up inside the non-return valve.

Shut off the pipeline and disconnect the valve. Remove any blockages and clean or replace the components where necessary.

Backflow

If you notice that a degree of backflow has started to occur, this is likely an issue with the internal component inside the non-return valve. The most common issue is that the valve has stuck open, and may require cleaning, lubricating, or replacing entirely.

Disconnect the valve from the pipeline and make your checks, applying the correct solution where necessary, before returning the valve, and ensuring that it is properly installed.

Industry and regulatory standards for non-return valves

Before you select a non-return valve, you should make sure that it meets regulatory standards and compliance requirements, to ensure that it can provide a safe and effective operation. Here are some key aspects you should consider:

Industry standards

Industry standards define the design, performance, and safety requirements of non-return valves. Relevant standards for non-return valves include:

• ISO 14313: this covers the design and performance requirements for non-return valves that are used in the petroleum and natural gas industries.
• ASME B16.34: this provides guidelines for the design, materials, and testing of non-return valves used in industrial applications.
• BS 5155: this is a British Standard requirement for non-return valves used in water supply systems.

Regulatory bodies

Regulatory bodies exist to oversee the compliance of non-return valves across various industries, ensuring that they meet safety, and performance standards. Relevant regulatory bodies include:

• Water Regulations Advisory Scheme (WRAS): this body provides guidelines and approval in the UK for non-return valves used in water supply systems.
• American Water Works Association (AWWA): the AWWA provides certification in the US for non-return valves used in water treatment and distribution systems.
• Institution of Gas Engineers and Managers (IGEM): IGEM provides standards for non-return valves used in gas distribution systems.

Fulfil all your non-return valve needs with The Hosemaster

Looking for new parts for your piping system? At The Hosemaster, we stock both female to female, and male to female non-return valves across a variety of diameters – so you can find what you’re looking for when you shop with us.

If, at any point in your buying journey you have more questions, please feel free to contact us online, or call 01282 604 002 to speak to one of our knowledgeable members of staff.

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