What is check valve?
Check valves are commonly used to prevent backflow in pipes. A check valve is essentially a one-way valve that allows flow to travel freely one direction but closes if the flow turns to safeguard the piping, other valves, pumps, and so on. Water hammer can develop if the flow turns and no check valve is fitted. Water hammer frequently happens with high force and can easily destroy a pipeline or its components.
Where are check valves used?
Check valves are utilized in a wide range of applications. For example, they are frequently installed on the outlet side of a pump to protect it from backflow. Because centrifugal pumps, the most popular form of water pump, are not self-priming, check valves are required to maintain water in the pipes. Check valves are also commonly employed in HVAC (Heating, Ventilation, and Air Conditioning) systems. HVAC systems are utilized in huge buildings, for example, to pump coolant many storeys up. These check valves are designed to prevent the coolant from flushing back down.
Considerations when choosing a check valve
When selecting a check valve, it is critical to conduct a cost-benefit analysis of the specific system. The goal is generally to save money while achieving the lowest possible pressure loss, however with check valves, higher safety implies more pressure loss. To ensure that the check valve properly protects the system, each system must be evaluated individually, with factors such as the risk of water hammer, acceptable pressure loss, and the financial consequences of installing a check valve with an excessive safety margin against water hammer taken into account. For further information, please see How to Choose the Right Check Valve.
Check valves of various sorts
Check valves for water and wastewater applications come in a variety of styles. They function in various ways but accomplish the same goal. Swing check valves, ball check valves, tilted disc check valves, slanted seat check valves, nozzle check valves, and quiet check valves are all available from AVK. Go to our product finder to see the entire selection. Swing check valves and ball check valves are the most popular types of water and wastewater check valves:
- Swing check valves are characterized by a disc that swings on a hinge or shaft. The disc swings away from the seat to allow forward movement, and then swings back onto the seat to prevent reverse flow. The weight of the disc and the return flow have an effect on the valve’s shut-off characteristics.
- Ball check valves: A ball check valve works by moving a ball inside the valve up and down. The seat is machined to accommodate the ball, and the chamber is conically designed to guide the ball into the seat and seal it, so preventing reverse flow.
Water hammer and pressure surges
What exactly is water hammer?
Water hammer is created by a rapid shift in the velocity of a fluid in a pipeline system and is often caused when moving fluid suddenly comes to a halt, such as when it collides with an object. A valve that is closed too quickly, for example, may send a shock wave down the pipe, potentially damaging both the pipe and the apparatus. It will continue to flow up the pipeline until the energy has been released, causing a localized increase in pressure and loud noises, sometimes simulating a hammering noise, which is the noise of the pipe expanding under these conditions.
Why do pipeline pressure surges occur?
If a pump fails or a valve closes too quickly, the flow will continue, resulting in a vacuum downstream of the pump or valve and extremely high pressure at the opposite end of the pipeline. When two differing pressures exist in a pipeline, the flow will flow in the direction of the lowest pressure, causing a pressure surge. The flow will continue to move back and forth until the energy has been spent and the pressures have been equalized.
Although a pressure surge may only last a few seconds, it can increase typical system pressures by up to tenfold or more. Due to the formation of vacuum pressures, this can cause significant damage to the system, including pipe cracks, bursts, cavitation, and implosion. Aside from the expenditures and downtime that these failures cause, the health and safety implications are also significant. These failures may not be the result of a single huge pressure surge, but rather recurring surges that finally create system exhaustion.