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How Check Valves Influence Water Pressure in Pipelines？
Check valves, also known as "one-way" valves, are autonomously operated unidirectional valves that allow fluid to flow in a singular direction, thus reducing or preventing backflow. They are designed with key factors in mind, such as the fluctuating nature of the closing assembly and pressure changes in the fluid flow upon the closing of the flow restrictor. One important consideration when installing a check valve is the orientation in which it is installed.
Various accessories such as hinges, pistons, screens, and flaps are employed in different types of check valves. In simpler terms, however, a flap of some kind is used to allow flow in one direction while restricting it in the other, hence the name “one-way valve.” The way the flap moves with the fluid flow is where most check valves differ. It may be supported by a spring (double door check valves), by gravity (swing check valves), or by a combination of both. Types of check valves include ball check valves, Y-type check valves (sometimes used with swing or ball check valves), and foot valves, which incorporate a screen and are typically used at the end of a pipeline.
Water Flow and Pressure in Piping Systems
Water pressure is the force exerted on water to push it through the pipeline. This pressure may be naturally created (gravity) or artificially created (pumps). Water flow, on the other hand, is the amount of water running through a pipe at any given time. To understand their relationship, consider the diameter of the pipe. With the same source, a wider pipe will allow more water to flow, but at a slower rate, due to less pressure exerted on it. However, the greater the amount of water flowing, the greater the pressure will be, and vice versa. Therefore, the flow-pressure relationship is not a simple one.
It’s important to be aware of the cracking pressure of the water check valve you are going to use. The cracking pressure is the precise upstream water pressure at which the valve opens, allowing a measurable flow of fluid through. The cracking pressure is influenced by the force required to open the check valve, which may depend on the tightness of the spring or the weight of a gravity-operated flap.
Several factors affect the pressure drop across a check valve, including the specific gravity of the fluid, the flow rate of the media, and the flow coefficient (Cv) of the valve. Increasing the flow rate of the media will lead to a higher pressure drop. Likewise, increasing the specific gravity of the fluid will also cause a higher pressure drop. Conversely, a larger Cv equates to a lower pressure drop.
Generally, gravity-supported water check valves, such as swing and tilting disk check valves, are best for horizontal and low-pressure applications, as the force required to open the restricting flap is minimal. However, they may be problematic in vertical applications. Spring-supported valves require higher water pressure to function but can be installed in either orientation and offer tighter backflow resistance. Restrictor water check valves are optimal for fluctuating water pressure situations due to their multi-spring assemblies, which allow you to set the cracking pressure of your choice.
Problems with Check Valves
Despite the many benefits, check valves can also cause problems that, if not addressed promptly, can result in significant damage to the piping system.
Mineral and Particulate Buildup: Depending on the fluid passing through, minerals and particulates can accumulate on the valve, especially on the closing assembly, preventing proper closure and disabling the valve's ability to stop reverse flow.
Chemical Compatibility: The material of the check valve, including the body and valve seat, must be compatible with the flowing media. Incompatibility can lead to valve failure. For example, saltwater will damage steel check valves but is compatible with polypropylene (PP) valves.
Reverse Flow: If the check valve is too slow to close or is oversized, reverse flow may occur. Similarly, if the valve is slow to open, water flow may be restricted, causing increased water pressure that can damage pumps and other fittings.
Water Hammer: Water hammer is one of the most common problems in piping systems. It occurs when a factor like pump shut-off or point-of-use closures forces the flow of media to stop or change direction, creating a hydraulic shock wave that can damage equipment, instrumentation, and pipes.
Why Valves Fail – and How to Fix Them？
As highlighted earlier, a failing check valve can cause significant damage to the piping system. However, valves often exhibit telltale signs of failure, which, if detected early, can prevent damage over time.
Excessive Noise and Vibration: These are often the first signs of a failing valve.
Wear and Tear: Internal valve components may show signs of excessive wear.
Reverse Flow and Water Hammer: These are strong indicators of valve failure.
To prevent valve failure, consider appropriate sizing, reaction speeds, and chemical compatibility. Installing filters, where feasible, will help prevent buildup and extend the life of your check valve.
If the valve is beyond repair, replacing it with a new one of the same type may be appropriate. In some cases, however, it may be necessary to replace the valve with a different type, especially if there are considerations about size, type, closing assembly, or reaction speed.
Need Guidance in Determining the Appropriate Check Valve?
If you're unsure which check valve is right for your application, feel free to contact us for expert advice.
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