Testing procedure for reduced pressure zone - backflow prevention transcript
  • Last updated:
  • 21 Feb 2020

For the RPZD test to be successful, both the upstream and downstream isolating valves must be tight.

The pressure difference across check valve must be 35kPa or greater. The relief valve vents to atmosphere at around 14kPa. If the second check valve holds tight, no measurement is required.

To test an RPZD, or a reduced pressure zone device, there are basically six steps we need to follow.

Firstly, we need to do our pre-test checks.

Second, we need to ensure that both the upstream and downstream isolating valves are not leaking.

Thirdly, we need to test the upstream check valve.

Fourth, we need to test that the relief port is operating effectively.

Fifth we need to check the downstream check valve, and six, we need to restore the valve to operating condition.

Firstly let's look at the pre-test checks. Before you carry out the test you must first clean and flush the line strainer and open the upstream isolating valve where necessary.

To test if the isolating valves are leaking, in sequence. open and close test tap one, test tap two and test tap three, to flush out any foreign matter. Ensure test kit valve A is open and test kit valve B is closed, and that C is open. Connect the high-pressure hose to test tap three. Slowly open test tap three and vent water through the vent hose. Then in sequence close test kit valve C and test kit valve B, and the upstream isolating valve. Note the differential gauge will indicate a high reading.

Slowly open test kit valve B, and drop the gauge pressure by 20kPa. Close test kit valve B. note the differential pressure gauge.

If the pressure on the gauge is rising, either the upstream isolating valve or the downstream isolating valve is leaking.

To determine which valve is leaking, open test tap one. If there is a continuous discharge of water from test tap one, the upstream isolating valve is leaking. If the pressure on the gauge is dropping or approaching zero, the downstream isolating valve is leaking.

Faulty isolating valves must be repaired or replaced and the test shall be repeated. Leaking isolating valves invalidate the test results.

To test the upstream check valve, firstly close test tap three. Open test kit valve C to relieve hose pressure. Disconnect high-pressure hose from test tap three. Clean the line strainer where fitted. Open the upstream isolating valve and ensure test kit valves A and B are closed. While test kit valve C is open. Connect the high pressure hose of the test kit to test tap one, and the low pressure hose of the test kit to test tap two. Open test taps one and two. Slowly open test kit valve A and bleed the water through the vent hose. Close test kit valve A. slowly open test kit needle valve B and bleed water through the vent hose to eliminate air from the system.

Slowly close test kit needle valve B and observe and record the reading on the differential pressure gauge. This indicates the pressure drop across the upstream check valve. If the reading is below 35kPa, the upstream non-return valve shall be deemed to be faulty and the valve shall be repaired or replaced, and the test must be repeated.

To test the relief valve, close test kit valve C and open test kit valve A. Slowly open test kit needle valve B, observing both the differential gauge and the relief port. Record the reading on the differential pressure gauge when the relief port commences discharging. If the reading is below 14kPa, the relief valve mechanism shall be deemed to be faulty and the mechanism shall be repaired or replaced, and the test shall be repeated.

To test the downstream check valve, close test taps one and two. Open test kit valve C and close test kit valves A and B. Disconnect the low pressure hose from test tap two, and reconnect to test tap three. Open test taps one and three. Slowly open test kit B and bleed water through the vent hose, then close test kit valve A. Slowly open test kit needle valve B and bleed water through the vent hose to eliminate any air from the system.

Slowly close test kit valve C and open test kit valve A. Observe the relief port for the presence of a continual discharge. If there is a continual discharge present, the downstream non-return valve shall be deemed to be faulty and the valve must be repaired or replaced and the tests repeated.

To restore the backflow prevention device to its operating condition, close test taps one and three. Open test kit valves A, B and C, and disconnect the test kit hoses, and open the downstream isolating valve. This restores the device to operating condition.

Guidelines for backflow prevention devices are available on council’s website.