Solving Water Hammer

Threaded check valve

Occurring in all types of piping systems, water hammer is a very common, but potentially very serious, issue. Also called hydraulic shock, water hammer occurs when a flowing liquid (or gas) in a pipe system is suddenly forced to stop. The momentum of the fluid abruptly stopping creates a pressure wave, which moves through the media in the piping. 
Everything in the system is then vulnerable to this extreme force. Often, the surge dampens or dissipates quickly. However, the waves, which can easily exceed five to 10 times the working pressure of the system, can place a great deal of stress on the system as a whole, causing significant — and even dangerous — problems.

The Causes of Water Hammer

A valve closing too quickly or a pump shutting down suddenly are the most common causes of water hammer. But various other circumstances can cause water hammer, including improper valve selection, improper valve location, poor maintenance practices, incorrect pipe or radiator pitch, near-boiler piping that doesn’t meet manufacturer specifications, bad steam quality, and an overfired boiler.

Other catalysts include insufficiently insulated steam pipes, a priming or surging water line, a long nipple on the Hartford Loop (where the equalizer and the wet return join), a flooded system, improperly dripped mains, a clogged gravity-return line, malfunctioning steam traps, and insufficient vertical space between the boiler water line and the end of the main. 

Certain types of valves — such as swing check valves, tilting disc checks, and double-door check valves — can also contribute to water hammer. Because these valves rely on reverse flow and backpressure to push the disc back onto the seat and allow the valve to close, they’re especially prone to slamming.

Recurring cases of water hammer can cause more than just irritating thumping and pounding noises. Consistent water hammer can seriously damage pipelines, pipe joints, gaskets, and all other components in a system, such as flowmeters and pressure gauges. It can also cause leaks at the joints in the system, cracked pipe walls, and deformed piping systems — all of which necessitate costly repairs and downtime.

Reducing the Risk of Water Hammer

Although some degree of water hammer is inevitable in piping systems, it is possible to significantly reduce the risks and effects with the use of accumulators, expansion tanks, surge tanks, blowoff valves, and other mitigating solutions. 

Also, installing a spring-assisted, non-slam check valve can greatly reduce — or even eliminate — the effects of water hammer. These one-way valves don’t rely on gravity or fluid flow for closure, so sudden slamming isn’t an issue. Instead, they close based on the decrease of differential pressure across the valve’s closure member. Another option is to install an air chamber — a vertical pipe in a wall cavity adjacent to the water valves where the water is turned on and off. Typically installed at critical locations throughout a building, air chambers prevent water from generating the pressure waves that travel through pipes and cause surges. 

Water pressure regulators can also be installed to prevent water hammer issues that result from high water pressure. These pressure reducer valves guard against surges that can damage water-supplied appliances, such as dishwashers. In residential settings, installing a pressure reducer valve where the main water supply enters the home is preferable to installing multiple air chambers, allowing for a simpler, more streamlined solution. 

Mechanical water arrestors are another reliable alternative for spaces where the use of air chambers is impractical. Typically used in commercial buildings, arrestors feature a spring and air bladder to absorb any water movement. Finally, it’s important to ensure pipe-mounting straps are secure and tight; these straps are used to attach pipes to framing in order to reduce pipe movement as media runs through the piping system. Water hammer can arise quickly if straps become loose.

Learn More

When water hammer occurs, the resulting shockwave can exert pressure at hundreds of pounds per inch. The results are more than just loud and annoying — they can be potentially devastating to your home or business, incurring extra costs, downtime, and labor needs. 
Although some water hammer is to be expected in any type of piping system, recognizing the signs of it and addressing the issue before it causes significant damage can save a great deal of hassle — and a great deal of cash.


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