How a Water Pressure Regulator Works

The Spruce / Michela Buttignol

A water pressure regulator (sometimes called a pressure-reducing valve, or PRV) is a specialized plumbing valve that reduces the water pressure coming into the home through the main water line. This valve brings down the pressure to a safe level before the water reaches any plumbing fixtures inside the home. Too much water pressure can cause many plumbing problems, so it is very important to keep the water pressure under control. Although it is not necessary for every plumbing installation, a water pressure regulator can be essential in situations where the municipal water supply enters the home at a very high pressure, or where water pressure is irregular.

Most home plumbing fixtures are designed to work best at a pressure of about 50 psi (pounds per square inch), but it is not uncommon for municipal water supplies to enter the home with pressures as high as 150 or 200 psi. If such high pressures is present on a regular basis, the strain can eventually cause joints to fail, faucets and other fixtures to leak, and appliances to break down. Clothes washers, dishwashers, and some other household appliances have built-in pressure regulators, but a whole-house water pressure regulator still offers protection to those appliances, and it also serves to protect all the pipes and fixtures throughout the house.

How a Water Pressure Regulator Works

A water pressure regulator is a dome-shaped brass fitting that generally is found just past the main shutoff valve, where the main water line enters the house. It usually has an adjustment screw on top. Inside, a water pressure regulator has a variable spring-loaded diaphragm that automatically widens and narrows depending on the amount of water pressure entering the valve.

When the water enters the regulator at high pressure, the inner mechanism constricts the diaphragm to narrow the flow of water. This can reduce the pressure into a range of 50 to 80 psi, greatly reducing the stress on pipes and fixtures installed past the valve. Conversely, when the incoming water pressure drops, the diagram opens wider to allow more water to flow through the valve. An adjustment screw on the top of the regulator can be tightened to increase the tension on the inner spring (thereby reducing the pressure of the water as it exits the valve), or loosened to allow water to flow more freely through the valve (thereby increasing the outgoing water pressure).

When the system is protected by a water pressure regulator, there is less stress on the inner valves of appliances, faucets and shutoff valves will be less likely to leak, and fluctuations in water pressure are evened out.

Do I Need One?

To determine if you need a water pressure regulator, test the water pressure of the main water supply to your house. You can buy a simple, effective pressure gauge at a local hardware or home improvement store. Screw the pressure gauge onto any hose bib or washing machine faucet and turn on the cold water tap to measure the water pressure. If the pressure is between 40 and 60 psi usually, then you should be fine, but water pressure that is frequently above 80 psi is probably causing excessive stress on pipes, fittings, and fixtures. City water pressure can fluctuate considerably, often increasing at night when the overall load goes down, so make sure to test at various times of the day. And during the test, make sure that water isn't being used anywhere else in the house, such as at garden spigots or appliances.

You can also ask your local water company, who will likely be able to tell you if a pressure regulator is recommended in your neighborhood.


Watch Now: How to Test Your Home's Water Pressure

Installation Tips

If you need a water pressure regulator, it is best installed immediately after the main shutoff valve controlling the water line coming into your home. This position allows the regulator to protect all pipes in your house, and it also makes it easy to quickly shut off the main water valve if you need to replace or repair the regulator.

If you already have an existing pressure regulator, it usually is quite easy to replace it with the same brand and model. Most manufacturers do not change the shape or size of their regulators, so a new one from the same brand should fit exactly as the old one did. It can be as easy as shutting off the water, disconnecting one or two union fittings, then replacing the regulator with a new one installed in the same way.

A new installation, on the other hand, is more difficult because it will require some work on the main water line. Unless you are fairly experienced at plumbing work, it may be best to call in a plumber, as the installation may require repositioning the main water shutoff valve to create the necessary space for the water pressure regulator.

After installation, test the water pressure, and adjust the regulator, if necessary. To adjust, loosen the locknut on the adjustment screw, then turn the screw up or down until the water pressure is at the desired level, as measured by a pressure gauge attached to a threaded hose bib somewhere in the home.


Like all plumbing fixtures and valves, water pressure regulators eventually grow old and fail. If you notice water hammering of any type, or experience variations or inconsistencies in water pressure, it may be a sign that the water pressure regulator is no longer working properly. Testing the water pressure at least once a year is always a good idea, or whenever you have questions about the regulator's effectiveness. If the regulator's adjustment screw no longer has any effect on changing the water pressure, the valve is due for replacement.

Remember that too much water pressure will put extra strain on the home’s plumbing systems and can cause toilets to run, faucets to drip, water hammer to occur in the walls, and in extreme cases, it can even cause burst pipes that can flood your house. For these reasons, a failing water pressure regulator should be replaced as soon as possible.