Introduce check valve

What is a check valve? Check valves are generally installed in pipelines to prevent backflow. A check valve is basically a one-way valve, in which the flow can run freely one way, but if the flow turns, the valve will close to protect the piping, other valves, pumps etc. If the flow turns and no check valve is installed, water hammer can occur. Water hammer often occurs with an extreme force and will easily damage a pipeline or components.

Where are check valves used? Check valves are used in many different applications. For example, they are often placed on the outlet side of a pump to protect the pump from backflow. Centrifugal pumps, the most common type of water pumps, are not self-priming, and therefore check valves are essential for keeping water in the pipes. Also, check valves are very often used in HVAC systems (Heating, Ventilating and Air Conditioning systems). HVAC systems are e.g. used in large buildings, where a coolant is pumped many stories up. These check valves are installed to make sure that the coolant does not flush back down.

Considerations when choosing a check valve: When choosing a check valve, it is important to make a cost-benefit analysis of the specific system. Focus is often to reduce cost and at the same time obtain the lowest possible pressure loss, but when it comes to check valves, a higher safety equals a higher pressure loss. So in order to make sure the check valve protects the system properly, each system has to be assessed individually, and factors such as the risk of water hammer, acceptable pressure loss, and the financial consequence of installing a check valve with a too high safety margin against water hammer have to be considered. Please go to How to choose the right check valve for more details. 

Different types of check valves: There are various types of check valves available for water and wastewater applications. They work in different ways but serve the same purpose. AVK offers a wide range of swing check valves, ball check valves, tilted disc check valves, slanted seat check valves, nozzle check valves and silent check valves. Go to the complete range in our product finder. The most common types of check valves for water and wastewater are swing check valves and ball check valves. 

Swing check valves: A swing check valve is mounted with a disc that swings on a hinge or shaft. The disc swings off the seat to allow forward flow and when the flow is stopped, the disc swings back onto the seat to block reverse flow. The weight of the disc and the return flow has an impact on the shut-off characteristics of the valve. 

Ball check valves: A ball check valve functions by means of a ball that moves up and down inside the valve. The seat is machined to fit the ball, and the chamber is conically shaped to guide the ball into the seat to seal and stop a reverse flow.