Pressure Reducing Valve



What Is a Water Pressure Reducing Valve?

PRV
Also known as a water pressure regulator valve, these are inexpensive, compact mechanisms that provide us with two basic functions: First they reduce any high water pressure that is supplied to us from city water mains. A PRV can give us a lower, more functioning water pressure to distribute throughout our homes.  Secondly, these valves not only reduce excessive pressure but also regulate it by maintaining a set pressure downstream of the valve. This insures that the dwelling’s fixtures, piping and appliances function at a safe, consistent pressure. Pressure reducing valves are typically located directly after your water meter and have an adjustment screw for setting desired pressure.

Two Basic Types Of Pressure Regulating Valves
  • Direct Acting Valves

    This is the most commonly used PRV, especially in a residential application. They have a simple design and are an economical choice.

  • Pilot Operated Valves

    This type of regulating valve is typically for larger diameter pipe, which makes them ideal for commercial and industrial work.

What Is Water Pressure?

When opening a plumbing fixture in your home water is forced out by a “push”. This “push” can be measured in pounds per square inch (PSI). This reading is a measurement at which the water is forced through. Also, the higher the force the higher the velocity in which the water moves through the piping. So in short, the higher the pressure (PSI), the stronger the “push”.
Low Pressure Push_edited-1
High Pressure Push

What Is Wrong With High Water Pressure?

Let’s be honest, having “low water pressure” just doesn’t sound all that great. But the fact of the matter is, it’s very important to reduce excessive water pressure. And truly, a lower water pressure has little effect on the overall performance of your plumbing fixtures, so you need not worry. Your fixtures are designed to work optimally between 50 to 80 psi and anything above that can cause problems.  High water pressure is much like high blood pressure within the human body. Excessive pressure can damage your organs overtime much like your fixtures. Here are a few problems with high water pressure:

  • Water Heater Leaks

    High pressure causes your temperature & pressure safety devices to open and leak.

  • Banging Pipes

    The velocity of your high water pressure can slam into your pipes causing them to rattle.

  • Dripping Faucets

    Pressure can force out water through your faucets and damage internal parts.

  • Damaged Appliances

    Excessive pressure can wreck havoc on the devices that turn your appliances off and on.

  • Leaking Pipes

    Excessive pressure causes water piping to fail prematurely.

  • High Water Bills

    Higher the pressure higher the flow, which results in higher monthly cost.

A Faucet With A 10 Minute Running Time:
@ 50PSI (Ideal Range)
30 Gallons Of Water Used
@ 65PSI (Moderate Range)
36 Gallons Of Water Used-6 Wasted
@ 80PSI (Maximum Range)
40 Gallons Of Water Used-10 Wasted
@ 100PSI (High Pressure)
45 Gallons Of Water Used-15 Wasted
@ 150PSI (Very High Pressure)
56 Gallons Of Water Used-26 Wasted
Flow CostThe diagram on the right shows how water pressure can effect water usage which in turn directly effects cost. This is a diagram of a faucet with a 10 minute running time. As you can see, more water is used preforming the same task. For instance, taking five minutes to brush your teeth with a normal water pressure vs a high pressure has a difference in cost. So, reducing high water pressure can really have long term savings.

Why Is City Domestic Water Pressure So High?

hydrant3
Higher water pressures are put into place for good reason. This excessive pressure is to accommodate for such things as high-rise buildings and elevation changes, to overcome pressure loss. Our cities also need sufficient water pressure to accommodate for fire protection, such as hydrants and fire sprinkler systems. This all starts first with pump stations that draw water from nearby treatment facility. These pumps will then distribute water throughout the city or fill elevated storage tanks (water towers) for distribution.

How Exactly Does A Water Tower Work?

A water tower is an elevated structure supporting a water tank constructed at a height sufficient to pressurize a water supply system. This system is then used for the distribution of potable water and emergency storage for fire protection demands.

Water towers are able to supply water even during power outages, because they rely on hydro-static pressure produced by the elevation to push water into domestic and industrial water distribution systems. However, the water tower cannot supply water for a long period of time without power, because an electrical pump is typically required to refill the tower. A water tower also serves as a reservoir to help with water needs during peak usage times. The water level in the tower typically falls during the peak usage hours of the day, and then a pump fills it back up during the night.

How Does A Water Tower Creates Pressure?

Below is a non-scale drawing of a potable water distribution system using elevated storage. This is a general concept of how water pressure can be created within a city. This example gives us an understanding of how pressures can differentiate based on a structure’s elevation in relation to a water tower. It also tells us why some structures are more susceptible to excessive pressure and are in need of a pressure regulating valve. If provided with height measurements, we can use simple math to determine the approximate pressure at each fixture.
Elevated Storage Tank



  • Fixture 1

    Noticing the elevation in relation to the water source in the tower we can determine our water pressure. 0n average with every 2.3 vertical feet downward from the water tower’s highest level we gain 1psi in water pressure. So, this would make this fixture’s pressure roughly 9psi and it would not require a pressure reducing valve.

  • Fixture 2

    Moving on to the next fixture, we examine the elevation in relation to the water source again. Knowing that the top of the water source represents 0psi and we are 150′ away, we can use our formula again. This fixture’s pressure would be 65psi. This fixture is starting to gain excessive pressure but is not in the red zone.

  • Fixture 3

    The last fixture’s elevation in relation to the water tower is roughly 200′. This fixture would require a pressure regulating valve because its pressure would be close to 87psi, which is over the recommended limit.

I Already Have A PRV But My Water Pressure Is Still High!

Unfortunately, pressure reducing valves get tired and give up. This is very common in the plumbing service world, we see this a lot. The good news is, it has more than likely served its purpose by protecting your fixtures over the years. If you suspect high water pressure don’t put it off for too long, you’ll be sorry you did.