Understanding Water Hammer in Well Systems
Water hammer is a pressure transient that occurs when the velocity of water in a pipeline changes abruptly. The term comes from the audible knocking or banging that results, a sound often mistaken for someone striking the pipe with a mallet.
Water Hammer in Conventional Well Installations
In a standard well setup, water hammer typically develops under one of two conditions:
- The check valve on the drop pipe is positioned more than 30 feet (9 meters) above the water level, or
- A check valve on the drop pipe fails to seal properly while a check valve installed higher in the system holds tight
In either scenario, an air gap or partial vacuum forms in the section of pipe between the two points. When the pump restarts, water rushes to fill that void at high velocity, then slams into the closed check valve and the motionless column of water above it. That sudden deceleration generates the pressure spike responsible for the hammering effect. Left unaddressed, repeated surges can crack pipe joints, rupture pipeline sections, or place added mechanical stress on the pump and motor. If you notice these symptoms, shut the system down and contact a qualified pump installer to diagnose and correct the issue before restarting.
Water Hammer in Submersible Pump Systems
Submersible pumps experience water hammer through a slightly different mechanism: a sudden stop in flow velocity sends a pressure wave oscillating back and forth through the pipeline until it dissipates.
Here’s how it plays out: when the submersible pump cycles off, the water column above it begins draining back down toward the pump. The check valve reacts instantly, snapping shut to block that reverse flow. The moving water slams into the now-closed valve, and the resulting pressure wave travels back up the pipe until it reaches the nearest closed point (a valve or fixture), then rebounds downward again. Each successive bounce loses energy, so the hammering is usually heard once or a few times in quick succession before the system settles.
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