Introduction to check valves
What is a check valve?
Check valves are one-way valves and are installed in pipes to prevent backflow. A check valve allows the flow to flow freely in one direction, but if the flow reverses, the valve automatically closes to protect the pipes, other valves, pumps, etc. If the flow reverses and a check valve is not installed, water hammer can occur. Water hammer is a phenomenon that occurs with extreme force and can cause significant damage to the pipe or its components.
Where are check valves used?
Check valves are used in a wide variety of applications. For example, they are often placed on the discharge side of a pump to prevent backflow and thus protect the pump. Centrifugal pumps, which are often used in water supply systems, are not self-priming, so check valves are essential to keep water in the pipes.
Check valves are also often used in HVAC (heating, ventilation and air conditioning) systems. For example, HVAC systems are used in large buildings where coolant is pumped up many floors. Check valves are installed here to ensure that the coolant does not flow back, keeping the system efficient and preventing damage.
Considerations when selecting a check valve
When selecting a check valve, it is important to thoroughly evaluate the application needs and perform a cost-benefit analysis. Often the goal is to reduce costs while achieving the lowest possible pressure drop, but with check valves, increased safety equals increased pressure drop. To ensure that the check valve protects the system, each system must be individually evaluated for factors such as the risk of water hammer, acceptable pressure drop, and the financial implications of a check valve with too high a safety margin against water hammer. View our page.
Please go to How to choose the right check valve for more details.
Types of check valves
There are several types of check valves available for water and wastewater applications. They operate in different ways but serve the same purpose of preventing backflow. AVK offers a wide range of check valves including ball check valves, soft and hard seated butterfly check valves and nozzle check valves. The check valves can be installed both horizontally and vertically and are easy to maintain. The most commonly used check valves for water and wastewater are check valves and ball check valves.
Please go to our product pages Swing check valves and Ball check valves for more details.
Water hammer and pressure waves
What is water hammer?
Water hammer occurs when the velocity of a fluid in a piping system changes rapidly, usually due to a sudden cessation of flow caused by an obstruction. For example, this can happen when a valve is closed too quickly. A rapid change in velocity sends a pressure wave through the pipe, potentially damaging both piping and equipment.
This pressure wave continues to travel through the pipe until the energy is dissipated, and can cause a localized increase in pressure and produce loud hammering sounds.
Why pressure waves occur in pipelines?
Pressure waves occur when a pump stops or a valve closes too quickly, allowing flow to continue and creating a vacuum downstream of the pump or valve, while very high pressure builds up at the other end of the pipe. When different pressures are present in the pipe, the flow will move toward the area of low pressure, creating a wave that continues to move back and forth until the energy is dissipated and the pressure has stabilized.
Although a pressure wave may only be short-lived, it can increase system pressure by a factor of 10 or more, potentially causing serious damage such as pipe rupture, bursting, cavitation or implosion caused by vacuum pressures. In addition to repair costs and operational downtime, such incidents pose significant health and safety risks. In addition, repeated smaller pressure waves can lead to fatigue failure of the system over time.
