How to Test a Backflow Preventer

backflow preventer
  • 1-2 hours
  • Intermediate
  • 20-60
What You'll Need
Waterpressure gauge
What You'll Need
Waterpressure gauge

Learning how to test a backflow preventer is important, since there are over 10,000 reported cases of backflow contamination each year, some of which are fatal. Backflow prevention devices are required by law and must be installed.

A typical backflow assembly has test cocks and shut-off valves and must be checked yearly and when installed or when relocating, in accordance with the state or district’s plumbing or building codes. You should note that the testing kits are expensive, and should therefore decide whether renting one might be more appropriate. If buying, make sure that you keep your tools clean, and check them annually for calibration.


There are several types of backflow test equipment that are available from multiple manufacturers. The better-known Backflow Preventer Test Kits are:

  • Model TK-7
  • Model TK-9A
  • Model TK-99D Delta Lite

All should possess a 0 to 15 psi range and a working pressure of 500 psi. Several manufactured testing kits come with gauge, hoses and fittings.

Step 1 - Shut off Water Supply

shutoff knob

First and foremost shut off the water supply. Warn people in the house not to use any water until backflow testing is completed and the water pressure restored.

Step 2 - Investigate Device and Direction of Water

There are two kinds of backflow devices: a reduced pressure principle device and double check valves. Examine the kind of device that you will be testing. Also investigate the direction of the water flow. Arrows or wording provided by the manufacturer on the device will inform you.

Step 3 - Gather and Number Cocks

Gather the amount of test cocks and bushings that you need. Ascertain that they are clean and free of debris or dust, and number the cocks.

Step 4 - Observe Valve

Shut off the downstream (number 2) shut-off valve. Wait several minutes when testing a reduced pressure principle device before hooking up the test kit hoses. Emanating water from the valve indicates that the first check valve is most likely fouled and needs to be serviced before you can continue. Exiting water from the double check valves, however, are not indicative of any concern.

Step 5 - Follow Instructions

parts of a backflow system

The test kit hoses come with instructions. Follow their instructions in hooking them up according to the device that you are testing. Since there are different tests according to the device being tested and according to the specific test run, and since each local municipality, county, and state has its own testing requirements, you are advised to access and follow their guidelines.

Step 6 - Test

Turn on the water and run a few taps at once. The water should be trying to run backwards through the system. Check whether the relief valve opens. If it does, you may need to replace it. Also check the water pressure inside the valve by using the gauge. If pressure is rising as the water struggles to flow backwards, you might have to consider replacing the valve.