Water Pipe Hammer

[bmac]

How do I stop water pipe hammer? Pipes vibrate (moan) when water is turned off (sometimes while still running).

bmac

[HayZee518]

Pipes that have a long run and are not fastened to the structure "move" when water goes through them. Hot water lines expand when water goes through them. You are gonna need access to the inside of the wall and install a vacuum breaker or at least an expansion nipple at the highest point in THAT run. Expansion Nipple - about a foot length of pipe - capped at the highest end of the run. This provides a shock absorber when the water is shut off.

[LazyPup]

The problem has nothing to do with the heat of the hot water. Technically speaking there is a law in Physics that states when the VELOCITY of a fluid (Liquid or gas)increases, the pressure DECREASES and conversely when velocity is decreased pressure increases. At static rest (faucett closed) the water is at constant pressure determined by the source pressure, either municipal water supply or well pump. When a faucett is opened water flow begins (incresing velocity) and the pressure in the line drops proportional to the rate of flow. With a faucett wide open the internal line pressure may typically drop as much as 1/2 the applied pressure. When the faucett is closed the pressure immediately rises to equal the applied pressure. The sudden and immediate rise in pressure causes a physical shock to the pipe which results in a banging sound which we call "water Hammer" ....TO PREVENT WATER HAMMER the pipes should be supported by approved hangers at not more than 4 foot intervals. In addition; a WATER HAMMER ARRESTOR is to be installed at or near the highest point in the water supply system. You can buy ready made water hammer arrestors at any building supply, plumbing supply or hardware store, or you can make one by simply installing a tee fitting, stub a piece of pipe up 10 to 12 inches and capping the top. In operation as the water is restored air is trapped in the vertical riser. Air is compressible whereas a fluid is not, so as the water rises in the tube the air is compressed until the pressure of the trapped air is equal to the water pressure. When water flow begins, the water pressure drops, the air expands and all is well. The moment the faucett is turned off, the internal line pressure immeditately rises, again compressing the air, which absorbs the shock. The code requires at least one water hammer arrestor be installed at the highest point, but, Water hammer arrestors should also be installed in the immediate vicinity of fast acting valves. The electro-magnetic solenoid valves in washing machines and dishwashers are fast acting valves, therefore, a water hammer arrest should be installed on the DW and Washing machine supply line. In the previous post it ws mentioned to use a vacuum breaker. VACUUM BREAKERS WILL NOT WORK and should only be installed on outside hose bibs or laundry faucetts equiped with an extension hose. The purpose of a vacuum breaker is to work as a check valve to insure that contaminated ground water can not be sucked up a hose and back into the potable water supply. Vacuum breakers are required on all outside hose bibs on a commercial plumbing installation and may be required on residential services depending on your local code. R. Rinard-journeyman plumber

[bmac]

That makes good sense.

Thanks alot guys.

bmac