SLAM! Not only could you hear the check valve slam inside the pump house at this mining operation, but you could also feel the ground shake and see the pump house rock. The force of the water returning down the discharge pipe and slamming the check valve shut was enough to cause serious concern among the maintenance personnel, who believed the water hammer was causing damage to the pump, pipes, and valves.
Water hammer can cause serious damage to pumping systems. It is caused by a sudden change in momentum inside the pipe. Fluids are non-compressible and contain a lot of mass. As the fluid travels through a pipe, it also has velocity. When a valve is suddenly closed, the energy from the velocity and mass can no longer travel forward, so the energy transfers into the valve and pumping system. This causes a spike in pressure that travels as a shockwave through the pipe.
How water hammer is solved depends on several factors, including which type of valve is closed. Ball valves, gate valves, and other rotational valves require that the valve be closed slowly to minimize water hammer. Check valves, on the other hand, require a different solution.
As we all know, check valves are open or closed by flow through the pipe. When flow stops, reverse flow passes by the check valve disc before the valve is completely closed. The reverse flow forces the valve shut and causes the loud noise and shockwave.
To prevent water hammer with check valves, the valve must be able to close in a fraction of a second, or it must have a controlled slow closure with the aid of an oil dashpot, or another device. The pumping system will determine which is best for the application.
A low-head, relatively flat system allows for slow closure of the check valve. A system with high head, such as the system at the mine with a vertical pipe, requires very rapid closure (e.g. 20 milliseconds) to prevent water hammer.
Here is a video from Val-Matic that shows how faster check valve closure can reduce the negative effects of water hammer.
The pump house at the mine contained a large submersible pump, one capable of pumping 4,500 gpm. A swing check valve was installed on the discharge side of the pump on a vertical pipe. Every time the pump stopped, water in the vertical pipe would rush back towards the pump and slam the check valve shut. The water hammer rattled the piping, the very expensive pump, and the pump house.
Before serious damage could result from the water hammer, the production manager called on Crane Engineering to see if we could help solve the problem.
After a conversation with valve experts Ted Genske and John Witek, they suggested replacing the check valve with a Surgebuster® check valve from Val-Matic. Genske and Witek recommended this valve due to:
In just a few days, the new valve was delivered to the mine and installed. The next time the pump was turned off, the maintenance team noticed a huge difference. Instead of a slam that shook their pump house, they felt a small vibration that had minimal effect on the pipes, pump, and surrounding structure.
The mine has taken note of other check valves with slamming issues and hopes to replace them with the Surgebuster®.
Water hammer causing problems with your pumps and pipes? Ask us about it! We gladly provide technical assistance to businesses and municipalities in Wisconsin, Minnesota, Iowa, and upper Michigan.