Water utilities have to be cautious with a phenomenon known as water hammer. This happens when a fluid (or gas) is stopped or redirected suddenly, such as when a pump turns off without first ramping down. Like a train wreck, the fluid in motion crashes against the pipe or valve and sends shockwaves back through the system.
An everyday example of water hammer often wakes people up at night. When a household appliance automatically shuts off water, you will often hear pipes banging or shuttering. This is a direct result of water hammer. It may seem innocent enough at home, but in industrial settings it can get out of hand.
Depending on a few factors, such as water velocity and pipe diameter, the shockwave from water hammer can be several thousand PSI. In severe cases, this can break pipes, fixtures, and anything else in its path – including pressure transducers. The thin diaphragm on a transducer can be flexed too much, causing permanent distortion.
There are several safety measures that can be taken, many of which have to do with system design. Specific to pressure transmitters, a snubber can be used to protect the diaphragm of the sensor. However, a snubber cannot protect against sustained pressure – anything more than a few milliseconds.
One of our water utility customers in Florida was having trouble with finding a pressure sensor that would withstand water hammer. They finally chose to install one of our PT-400s on their force main, and have since been very happy. They recently commented to us during a field visit that it was the only pressure transducer that would handle water hammer in their system. Considering the destructive power behind water hammer, we took it as quite the compliment.
Let us know if you have any concerns about your pressure transmitters and water hammer. We’d love to hear what steps you’ve taken to prevent damage.