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What Is Water Hammer and How to Stop It?

Chances are, you’ve probably heard loud banging and knocking sounds from your pipes at some point. Fluid motion can create a lot of pressure in your plumbing system. Water hammer in plumbing occurs when valves are used to manage the flow of liquids or steam close; it’s essentially a result of a pressure surge. A shockwave travels through a plumbing system at high pressure, causing fluid in motion to suddenly stop or change direction.

How Water Hammer Is Triggered

When water hammer occurs, it’s often triggered by a valve closing at the end of a pipeline. Tilting disc, swing, and double door check valves tend to close very rapidly, creating high pressure, but water hammer can be caused by pump failure as well. Water is an incompressible liquid, so an impact against a closed valve causes a shock wave that propagates at the speed of sound. It will continue until it hits the next pipe elbow or end of a pipeline.

In homes, water hammer often occurs when a washing machine valve closes after the drum reaches full capacity. Water continues to flow rapidly. It has nowhere to go, so slams against the side of the pipe, which can bump against other pipes or the frame in the wall.

Effect of Water Hammer on Plumbing Systems

Water hammer may happen momentarily, but it can cause a sudden plumbing failure or lead to damage over time. It may occur due to excess water pressure in supply lines, or perhaps plumbing pipes have come loose. Pumps, valves, expansion joints, gasketed joints, and welded joints can be seriously damaged, as can various fittings and connections. Water leaks, ruptured pipes, and property damage can result.

How to Stop Water Hammer

If water hammer is occurring in your home, there are steps you can take to alleviate it. Here are some effective measures:

  • Drain the Air Chamber: Home plumbing systems often have an air chamber to absorb the shock of water when a valve closes. Located inside walls, an air chamber can become waterlogged. This can be fixed by draining your plumbing system, which requires turning off the main water valve and opening the highest faucet in your home. Then drain water from the lowest faucet. The chamber should fill up with air once the water is drained and resolve your water hammer problem.
  • Install a Water Hammer Arrestor: This device has an air-filled cylinder to absorb the impact of abrupt increases in water pressure. Most water hammer arrestors install between the shut-off valve and supply line via screw-type connectors. One arrestor should be installed on the hot-water supply line and another on the cold-water supply line.
  • Adjust the Water Pressure: If the water pressure in your pipes is too high, the steps above will only work temporarily. You can regulate the pressure by adjusting the pressure-reducing valve, which is often located where the main water supply enters your home. To adjust the valve, turn the handle or, if necessary, with a wrench or screwdriver. The setting should be below 50 pounds per square inch (psi). Reducing water pressure also conserves water, saves energy, and can prolong the life of plumbing appliances.
  • Tighten Your Water Supply Lines: Sometimes, the U-shaped straps to fasten water pipes to wooden joists or studs aren’t tight enough. As a result, pipes can shift and cause noise. You can fix the problem by tightening the screws holding loose pipe straps. Additional straps can be added as well to improve stability. Pipe straps are usually made of thin metal or plastic, while padded types are available to reduce vibration.
  • Insulate Water Supply Lines: Foam pipe insulation not only prevents pipes from freezing. These tubes can also create a cushion for loose pipes. They fit easily over your water supply line and can usually be purchased in six-foot lengths.


Contact Village Plumbing and Air for Water Hammer Help

Water hammer in plumbing can lead to serious damage if not corrected. If you’re not comfortable attempting the steps above, our trained plumbing technicians can help. We provide piping and re-piping services in homes across the Houston area. Request service online or call 713-526-1491 to schedule an appointment.

One Response

  1. My water hammer problem is in my condo building. It is hammering pretty much constantly (I thought water had to be moving for water hammer to be active). I’ve drained the system as described and turned the water back on. It solves the problem temporarily but the constant hammering is back after a certain valve is opened… eventually. Do you think the water pressure is too high to the building?

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