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Water Hammer 101: Common FAQs

19 June 2019 by Clara Fernandez

You have the washing machine on in the laundry room, the dishwasher on in the kitchen, or maybe even the faucet turned on in the tub. When the water is shut off, there is a sudden loud knocking coming from somewhere in your water pipes. This bothersome problem is known as water hammer, and it can be incredibly annoying to contend with and hard on your pipes. To get familiar with this common plumbing issue, take a look at some of the most common questions about water hammer and the answers you may want to know. 

What exactly causes water hammer?

Water hammer is caused by the sudden shut off of water in a plumbing line. When the flow of water is disrupted suddenly, it sends a hydraulic shock back through the line. It is more common for the problem to happen when a water line is feeding an outlet at a rapid rate and then is quickly disrupted. For example, a washing machine fills the tub pretty rapidly but has a solenoid that instantly cuts off water flow when the tub is full. Some plumbing systems will only experience the water hammer issues when a specific appliance is operating. 

Why is water hammer more common in older homes?

There are a few reasons why water hammer may be more common in older homes. For one, pipe systems may not be quite as secure in older homes, which can cause them to rattle and shake to hit surrounding fixtures or wood. Sometimes the problem is relative to improper airflow too, especially in tighter installations where there is a series of pipes crammed into one spot. It is not uncommon for modern pipes to be installed in a way that prevents that hydraulic shock that causes water hammer symptoms. 

How can the problem be prevented?

Traditionally, water hammer was solved by installing air chambers that set atop a line to allow the excess air to kick up into that chamber when a hydraulic shock happened. This air chamber would sort of cushion the effect and minimize the problem. However, there are other solutions these days that are far more effective and practical. Water hammer arrestors are capable of absorbing all of the force from a shock wave when water pressure is suddenly disrupted. These arrestors contain a piston inside that moves to absorb the shock when it happens so noises are kept at bay and damaging pressure is absorbed. 

To prevent or address water hammer, be sure to reach out to local plumbing repair services.

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