backflow test kits

How to Use a Backflow Test Kit: A Step by Step Guide for San Diego Plumbers

August 23, 2025

Backflow prevention is a critical part of maintaining water safety, especially in regions like San Diego. The area has strict local regulations that aim to protect public water supplies from contamination. For certified testers and plumbing professionals, knowing how to use backflow test kits in San Diego properly is pretty important. Not only will proper use ensure compliance with local codes, but it will also help to deliver reliable service to clients across residential, commercial, and industrial settings.

This step-by-step guide outlines the correct procedure for using a test kit to evaluate common backflow prevention assemblies. The instructions below are based on general practices accepted in San Diego and throughout California, but always double-check with local municipal guidelines and manufacturer-specific recommendations.

Backflow Test Kits Explained

A backflow test kit is a precision instrument designed to measure pressure and flow within a backflow prevention assembly. It helps plumbers determine whether check valves and relief valves are functioning correctly and that no backflow or cross-connection threats exist.

Most test kits used in San Diego are differential pressure gauges with hoses, bleed valves, and accessories suited for testing the following types of assemblies:

  • Double Check Valve Assemblies (DCVA)
  • Pressure Vacuum Breakers (PVB)
  • Reduced-Pressure Zone Assemblies (RPZ or RPBA)
  • Spill-Resistant Vacuum Breakers (SVB)

These assemblies must be tested annually per city requirements.

Step-by-Step Guide to Using a Backflow Test Kit

Below is a general guide for using a test kit to check a Reduced-Pressure Zone Assembly (RPZ). We chose this particular kit because it is one of the most commonly used devices in high-hazard applications. The testing steps for other assemblies are similar but have distinct differences.

Be sure to check into the specific testing kit you are working with to fully understand the exact steps and measures that need to be taken. 

Step 1: Prepare the Area

Before beginning the test:

  • Ensure you have the correct tools: a properly calibrated backflow test kit, appropriate fittings/adapters, and the test form required by the City of San Diego.
  • Confirm that the assembly is accessible and has test cocks that are in good condition.
  • Notify the property owner or manager that the water will be briefly interrupted during testing.
  • Identify the make, model, and serial number of the assembly for documentation.

Wear appropriate PPE and relieve system pressure if necessary before attaching any gauges to ensure safety while following testing protocols. 

Step 2: Flush the Test Cocks

Flushing helps remove debris that can clog the test kit and provides accurate readings.

  • Slowly open each test cock (usually four total on an RPZ) one at a time, starting from the upstream side.
  • Use a flushing tool or hose to let water flow through each opening briefly.
  • Close all test cocks after flushing.

Step 3: Connect the Test Kit

Now connect the hoses from the test kit to the appropriate test cocks:

  • High side (red hose) to test cock #2 (between check valve #1 and #2)
  • Low side (blue hose) to test cock #3 (downstream of check valve #2)
  • Vent side (green hose, if applicable) to test cock #4 (relief valve port)

Ensure all valves on the test kit are closed before connecting.

Step 4: Bleed the Air from the Hoses

Air in the lines can cause inaccurate readings. To bleed:

  • Open the high and low side test kit valves slowly to allow water into the hoses.
  • Slightly open the bleed valves to let air escape.
  • Watch the gauge until the needle stabilizes and no bubbles are present.

Repeat as needed until all air is cleared.

Step 5: Test the First Check Valve

To test the first check valve:

  1. Close the downstream shutoff valve (after the assembly).
  2. Open test cock #2 (high side) and #3 (low side).
  3. Observe the differential gauge reading.

A properly functioning check valve should maintain a pressure drop of at least 1.0 PSI. Record the value.

Step 6: Test the Second Check Valve

Close test cock #2 and open test cock #4 (if testing the relief valve separately).

  1. Keep test cock #3 open.
  2. Observe the differential reading on the gauge.

The second check valve should also maintain at least 1.0 PSI to pass.

Step 7: Test the Relief Valve Opening Point

This part measures the point at which the relief valve opens under backpressure, which is a key function of RPZ assemblies.

  1. With test cock #2 still closed and #3 open, slowly open test cock #4 to the relief valve port.
  2. Open the high side valve on the test kit and begin applying pressure using the bleed valves.
  3. Monitor the gauge as pressure rises.
  4. The relief valve should discharge water at 2.0 PSI or higher.

If it fails to open or opens too early, the assembly fails and needs repair.

Step 8: Record Your Results

Using the San Diego-approved backflow test form, document the following:

  • Assembly type, manufacturer, model, and serial number
  • Date and location of the test
  • Differential pressure readings for each check valve
  • Relief valve opening point
  • Whether the assembly passed or failed

Submit the completed form to the appropriate authority, usually through the city’s online portal or via fax/email as specified. 

Step 9: Finish Up

Once testing is complete:

  • Close all test cocks
  • Remove the test kit hoses
  • Reopen the shutoff valves
  • Check for leaks or residual water discharge
  • Clean and dry your test kit for future use

Always leave the work area as you found it or better.

Tips for Accurate Backflow Testing

  • Calibration matters: Ensure your test kit is calibrated annually or as required by local guidelines.
  • Use proper fittings: Incorrect adapters can result in leaks or inaccurate readings.
  • Label your hoses: Red (high), blue (low), and green (vent) can help avoid mix-ups during setup.
  • Stay current on local codes: San Diego may update its backflow requirements periodically.
  • Replace worn parts: Test cocks, O-rings, and fittings wear out, so inspect them regularly.

Get Your Backflow Test Kits in San Diego from One Stop Backflow Supply

Proper use of a backflow test kit is a professional responsibility. In a city like San Diego, where water safety and compliance are strictly monitored, plumbers must be equipped not only with the right tools but also with the knowledge to use them correctly.

For high-quality, reliable backflow test kits in San Diego, along with fittings, accessories, and support for professional plumbers, consider One Stop Backflow Supply. Our team specializes in products and training materials to help licensed testers work more efficiently and confidently in the field. Check out the options today.