In commercial fluid control systems, preventing backflow is vital for preserving their integrity, safeguarding the hardware and equipment, and ensuring they function correctly and safely.
Check valves and strainers provide a reliable and solid solution, operating automatically to allow flow in one direction while blocking the reverse flow.
Understanding how check valves work in the context of fluid control and management, and knowing how to choose the most appropriate type, can prevent costly equipment damage, contamination issues, and extensive, unplanned operational downtime.
What is a Check Valve?
A check valve, also known as a non-return valve or one-way valve, allows fluid to flow in a single direction whilst preventing backflow.
When installed correctly, high-quality check valves:
- Protect pumps from reverse rotation
- Prevent contamination of clean water
- Maintain adequate system pressure
- Avoid water hammering in pipework
Check valves operate automatically based on the rate of differential pressure, and do not require any external power source or control signal to work. When pressure on the inlet side excess the outlet side by a certain threshold, the valve opens. If flow attempts to reverse, or if the inlet pressure drops unexpectedly, the valve closes, thus blocking backflow.
How Do Check Valves Work?
As said above, check valves are reliant on differential pressure. Each valve has a minimum pressure threshold to open, which is known as the cracking pressure. Most industrial check valves possess a cracking pressure of 1 bar or lower.
When inlet pressure rises above this threshold, it overcomes the closing force (which could be via springs, magnetic forces, or gravity) and pushes the valve element away from its enclosure.
Once inlet pressure drops, or backpressure materialises, the closing mechanism returns the valve element back to its enclosure, thereby blocking the reverse flow.
The method and orientation of check valve installation matters profoundly. Most check valves contain an arrow on the housing or casing which indicates the correct flow direction. Accidentally installing a check valve backwards will prevent the forward flow entirely, and can cause a serious amount of pressure buildup, which could compromise the integrity of the entire underlying system hardware.
Types of Check Valves
Different check valve designs suit different applications, each offering specific benefits.
Swing Check Valves
These valves feature a hinged disc that swings open under forward flow and closes due to gravity, and they can be installed vertically as well as horizontally. The design allows for minimal pressure drops, and is ideal for applications such as water distribution, wastewater treatment, and industrial processes. This comes as part of our pump sets.
Spring Check Valves
Spring-loaded check valves use spring force to hold the valve element against its seat. When the inlet pressure overcomes the spring tension, the valve then opens, and because the spring mechanism means that these valves can be installed in any orientation, the faster closure is preferred in some applications. They are best suited for pulsating flow or where rapid valve closure minimises the risk of water hammer.
Ball Check Valves
Ball check valves employ a spherical ball as the sealing element. Spring-loaded versions can be installed vertically or horizontally, while non-spring versions must be installed vertically with upward flow. These valves are ideal for applications with particulate-laden fluids, such as fire protection, irrigation and sump pumps, as the ball self-cleans while in operation.
Lift Check Valves
Lift check valves feature a disc or piston that lifts vertically off its seat to allow flow. These valves must be installed horizontally and their design suits applications requiring frequent cycling and can handle saturated steam, such as high-pressure water or boiler systems.
Double Check Valves
Double check valves incorporate two single check valves in series within a single body, providing enhanced backflow protection. If one check valve fails to seal completely, the second provides a failsafe backup. You’ll often find these valves in water supply systems where backflow could contaminate potable water.
Common Applications of Check Valves
Check valves serve essential functions across numerous other industries not named above.
- Plumbing systems – they prevent sewage backflow, maintain water heater pressure and preserve pump stability.
- Industrial process systems – they prevent products from being contamination and maintain a stable process flow direction.
- Heating and cooling systems – check valves maintain proper refrigerant flow direction, ensuring the pumps function properly.
- Fire protection systems – these valves ensure water flows towards sprinkler heads while preventing drainage.
- Oil and gas operations – check valves are deployed for pipeline protection, pump discharge lines and wellhead preservation.
Selecting the Right Check Valve
When choosing the right industrial check valve, several factors must be considered, including:
- Body material – to ensure it resists corrosion and possible elevated temperatures. This means choosing stainless steel check valves for corrosive environments, brass check valves for general applications, and cast iron check valves for chemical resistance.
- Connection size – to ensure it can integrate with the incumbent piping to avoid unnecessary pressure dips.
- Pressure rating – this must exceed maximum system pressure to provide adequate safety.
- Cracking pressure – this should be well below normal operating pressure to prevent chattering.
- Installation orientation – some designs require specific mounting positions, which may not be possible given the building fabric.
Protect Fluid Control Systems With Quality Products from Applications Engineering
Check valves represent a small part of a substantial protective system, preventing reverse rotation and contamination in some applications, while maintaining product and system purity. For applications where backflow could cause damage or safety concerns, check valves are an invaluable layer of protection.
Given that they operate autonomously, this provides much-needed reassurance, but that doesn’t mean that they shouldn’t be periodically inspected. Spring-loaded designs experience wear and tear, debris can accumulate, seals can deteriorate, and process fluids can corrode intricate components, which is why monitoring and replacement are vital.
If you’re aware that your check valves need replacing, Applications Engineering possesses a healthy amount of stock at our Sussex facility, which can be delivered in a timely manner. Alternatively, knowing the correct product to buy can be challenging if you’re unfamiliar with the system setup, so if you need help finding the right valve products for your system, get in touch with our experts who would be happy to point you in the right direction.
