Fix-it Guide:The Highs and Lows of Water Pressure

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Most appliances, valves, and fixtures that use water are engineered to take 50 to 60 psi. Mains deliver water at pressures as high as 150 psi and as low as 10 psi. Too much pressure is much simpler to cure than too little pressure.

Low pressure

The symptom of low pressure is a very thin trickle of water from faucets throughout the house. Chronic low pressure is typically found in homes on hills near reservoir level or in old homes whose pipes are badly clogged by scale and rust due to hard water. In many communities, periodic low pressure may occur during peak service hours through no fault of the home’s location or plumbing.

Remember that fixtures farther from the main water supply pipe get less water pressure than those nearer the main. Too-small pipes may aggravate the problem of low pressure, too.

If you add new fixtures, you may need to install a larger main sup ply pipe from the point where the water enters the house to the various branches of the supply network, in order to maintain satisfactory pressure.

Whatever the cause of chronic low pressure, you’ll probably want to think of improvements rather than complete cures. The latter are either very expensive or mechanically un feasible—they range from complete replacement of the plumbing to building your own reservoir in a tower tank above the house. Still, you can make modest improvements by flushing the pipes and by replacing the main supply pipe.

Flushing the pipes. A system showing early signs of clogged pipes can regain some lost pressure if the sys tem is flushed. To do this, take these steps:

• Remove and clean aerators on faucets.

• Close the gate valve that controls the pipes you intend to clean. It may be a shutoff valve on the water heater, or the main shutoff valve.

• Open fully the faucet at the point farthest from the valve, and open a second faucet nearer the valve.

• Plug the faucet near the valve (but don’t shut it off) with a rag.

• Re-open the gate valve and let water run full force through the farther faucet for as long as sediment continues to appear—probably only a few minutes. Close the faucets, re move the rag, and replace the aerators.

Replacing the main supply pipe. Be fore you decide to replace all the pipes in your house because of low pres sure, try replacing the one section that leads from the main shutoff valve to your house. If it’s a ¾-inch pipe, replace it with a 1-inch pipe. The larger size won’t increase the pressure, but the increased volume of water will compensate. And if you have a water meter, you can also ask your utility company to install a larger one.

High pressure

The symptoms of high pressure are loud clangs when the dishwasher shuts off or wild sprays when faucets are first turned on. High pressure usually occurs in houses on low-lying slopes of steep hills or in subdivisions where high pressure is maintained as a matter of fire protection.

If your house has particularly high water pressure, take precautions against appliance damage and floods.

• Turn off the main shutoff valve when you go on vacation.

• Turn off appliance shutoff valves, especially for a washing machine and dishwasher, when not in use.

Above-normal pressure can be cured easily and inexpensively by the installation of a pressure-reducing valve (see Ill. 91). This valve can reduce pipe pressure from 80 pounds per square inch (psi) or more down to a manageable 50 to 60 psi.

The method you’ll use to install a pressure-reducing valve depends on the type of pipe—galvanized, copper, or plastic—in your plumbing system. First, assemble the valve with the pipe fittings necessary to connect the threads of the valve to the existing pipe. Then, after shutting off the water supply, remove a length of pipe on the house side of the main shutoff valve long enough to accommodate the valve and the assembled fittings.

Install the valve, following manuf. instructions for pipe fitting. When the work is completed, you can turn the water back on. Be sure to check for any leaks in the new connections.

To minimize the water pressure, turn the adjusting screw at the top of the valve clockwise until the pressure is tow enough to end bothersome pipe noises. Be sure the valve still supplies adequate water flow to the upper floors or to far-away fixtures in the house.


Ill. 91. Install a pressure-reducing valve between the main shutoff valve and the house to minimize a high-pressure problem.


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Updated: Monday, December 13, 2010 13:12