What Is A Reduced Pressure Zone (RPZ) Valve?

Reduced pressure zone assemblies, also commonly referred to as reduced pressure zone (RPZ) valves or RPZ backflow preventers, are an essential system that prevents the backflow of clean water to avoid contamination.

RPZ backflow preventers are designed to prevent contaminated water from mixing into clean municipal water supplies and are commonly used by municipalities, homes, and commercial buildings. These valves provide reliable protection against back pressure and siphonage, safeguarding water supplies from any form of contamination.  

RPZ valves are pivotal in preventing toxic chemicals, hard metals, pesticides, and other harmful compounds from contaminating water supplies. In residential buildings, a RPZ device is used with sprinkler irrigation systems, boiler systems, fire suppression systems, and forced-air furnaces where it acts as a safety mechanism.

How Do RPZ Valves Work?

rpz valve

Image via Unsplash by kevin_butz

In a typical RPZ assembly, two one-way valves are connected to prevent water from returning to the supply line. This system works by ensuring that the incoming fluid has a higher pressure than the water entering the downstream supply. To prevent minor backflow leakage, the closure of one valve creates a pressure differential, thus tightening the valves and effectively sealing the system from backflow.

For a municipal water system, if at any time the pressure at homes exceeds the pressure on the supply side, the two RPZ valves close preventing backflow. If either of the check valves leaks, the relief valve is designed to open and discharge water to the outside, ensuring that water never returns to the supply line.

Because of their design, RPZ backflow preventers experience more high volume and pressure loss than double-check systems. Plumbers must account for these losses when designing drainage systems. Fluctuations of pressure, either downstream or upstream, will prompt the RPZ assembly to discharge small amounts of water periodically.

RPZ backflow preventers must be set up in areas with adequate drainage because a large volume of water will flow from the relief valve. For this reason, RPZ assemblies shouldn’t be installed in areas where the discharge water can cause damage — adequate drainage must be considered in areas fitted with RPZ valves.  

How Do RPZ Devices Prevent Contamination?

Rapid and unexpected reduction of pressure in pipelines can present an extreme risk of contamination to water supplies. When water pressure goes down, water flows in the wrong direction, bringing contaminated water from home appliances and other industrial processes with it. Even the slightest fluctuation in pressure can cause backflows and contaminations.

Also, use of pesticides or fertilizers in your backyard together with your home’s fire suppression system poses a danger. The standing water in your water supply system can get trapped and lead to bacterial and mineral growth, which can contaminate your clean water supplies.

When there is a water leak in your supply lines, hydrant flushing, city water main break, or use of hydrant to fight fire, pressure in the water system drops. When this occurs, a RPZ prevents backflows, effectively preventing clean water from backing up to supply systems hosting potential contaminants.

Installing RPZ Backflow Preventers

When installing RPZ valves, contractors should avoid installing them in areas prone to flooding, places above electrical equipment, and positions that expose the valves to mechanical damage. The area should also be in a heated enclosure to prevent freezing, which can lead to ice buildup inside the valves, which can block water from flowing.

Because of fluctuating pressures, designs should factor in the intensity and frequency of the fluctuations. For instance, installation of a single-check valve upstream of the RPZ valve prevents fluctuation of pressures upstream, which are usually the primary cause of frequent discharges through the relief valve.

Unless the valve is specifically approved for vertical installations, RPZ valves should be installed horizontally with the relief valve mechanism discharging downward. In order to prevent any fouling of the RPZ assembly elements, plumbing engineers should install in-line strainers upstream of the RPZ valve. The valves must be installed above the floor surface to facilitate easy and fast inspection, testing, and maintenance.

RPZ Valve Testing

After the installation process, the reduced pressure zone device installed on plumbing systems requires regular tests by certified plumbers. Illinois water protection codes state that RPZ valves must be tested at least once every year. These tests are essential as they ensure that the valves are operating efficiently to protect the city water supply and drinking water from contaminants.

Only a certified assembly tester should perform the RPZ backflow preventer test, using a properly calibrated tool. Testing procedures may vary from state to state, but it must comply with the Department of Health and Illinois Plumbing Codes. Building maintenance workers, contractors, and plumbers use RPZ testers to measure the pressure difference between two points.

Before beginning the test process, contractors must:

  • Get permission to shut down the water supply and notify the users of the impending interruption.
  • Determine the direction of flow (crucial in differentiating downstream and upstream).
  • Identify the test cocks.
  • Install testers.
  • Perform repairs if necessary.
  • Write a report.

The three-valve RPZ and the five-valve RPZ are the common RPZ testers approved for testing backflow systems. Since the five-valve RPZ tester allows testing procedures to take place without disconnecting any hoses, it is the most popular tester.

RPZ Calibration Tests

RPZ calibration tests should be done annually by accredited contractors and plumbers. While most companies only undertake calibration tests on the gauge on an RPZ tester, it is a good idea to test the system for leaks, inspect wear and tear of the valves, and account for pressure differences if any. Testing the entire RPZ assembly allows early detection of malfunction within the parts of the RPZ unit.

The Department of Health made it mandatory that all water systems that provide water for nonpotable use should use backflow preventer systems such as the RPZ. This means that public water supplies, commercial property owners, and residential property owners should install backflow systems to protect users from health hazards that can result from water contamination.

Contact Dahme Mechanical to Learn More About RPZ Valves & Prevention Testing

Whether you are a municipality or a property owner, complying with Illinois’ backflow protection codes means installing a robust backflow prevention system. Thankfully the team of experts at Dahme Mechanical Industries is fully certified and able to perform RPZ backflow prevention installation, testing, calibration and repair. We serve Arlington Heights and the surrounding communities, including Schaumburg, Des Plaines, Palatine, and more. Contact us today to learn more!