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newSchoolWorks.com › VoTechWorks › Building & Construction › Plumbing & Pipefitting › Backflow Prevention: Principles, Devices, and Field Testing › Lesson 9
BLD-PLUM06-08 · Lesson 9 · 16 clock hours · practice

Calibrated Test Kit Operation and Field Test Procedures: RPZ Assembly

Objective. The learner performs a complete ASSE field test on a reduced-pressure zone assembly, correctly tests the relief valve opening point and both check valves, and records findings on the standard form.

What Is a Reduced-Pressure Zone Assembly?

A reduced-pressure zone (RPZ) assembly is a mechanical backflow preventer designed for high-hazard cross-connections. It contains two independently acting spring-loaded check valves separated by a reduced-pressure zone, plus a hydraulically operated differential pressure relief valve (DPRV) vented to atmosphere between the two checks. If either check valve weakens or the pressure differential across the assembly falls to an unsafe level, the relief valve opens and discharges water rather than allowing contaminated water to back-siphon or back-pressure into the potable supply.

Because the RPZ protects against both back-pressure and back-siphonage under high-hazard conditions, it demands a thorough field test at installation and on the schedule required by the authority having jurisdiction.

Test Equipment and Pre-Test Safety

All RPZ field tests use a calibrated differential-pressure gauge test kit. The kit connects to the assembly's test cocks through flexible hoses fitted with needle valves. Before each use, verify that the kit is within its calibration interval — an out-of-calibration kit produces readings that cannot be trusted and may lead to a false pass or fail.

PPE and site safety: Wear safety glasses at minimum; the relief valve may discharge a burst of water during the test. Keep hands and face clear of the relief valve vent. If the assembly is located in a confined space or vault, follow your employer's confined-space entry procedure and ensure atmospheric monitoring before entry. If any upstream or downstream isolation requires working on pressurized piping, verify that the correct shutoff valves are closed before breaking any connection.

Connecting the Test Kit — Correct Order Matters

The five test cocks on an RPZ are numbered 1 through 5 (from the inlet side). The standard connection sequence prevents water hammer and keeps the kit from flooding:

1. Close all needle valves on the test kit.

2. Attach the high-side hose to test cock No. 2 (upstream of Check Valve 1).

3. Attach the low-side hose to test cock No. 3 (the zone between the two checks).

4. Open test cock No. 2 slowly, then open the high-side needle valve — the gauge is now reading supply pressure reference.

5. Open test cock No. 3 slowly, then open the low-side needle valve — the gauge now reads the differential across Check Valve 1.

6. Use the bypass/equalizer valve on the kit to zero and bleed air before taking readings.

Never open a test cock before the corresponding hose is firmly seated; a loose connection under pressure can cause injury.

Testing the Relief Valve Opening Point

The DPRV must open before the zone pressure rises to equal the inlet pressure. To test it:

1. With the kit connected between test cocks 2 and 3, slowly close the No. 2 shutoff (inlet) to reduce the differential.

2. Watch the gauge; when the differential drops to the relief valve's opening point, water discharges from the vent port.

3. Record the differential at which the relief valve first opens. A passing result requires the relief valve to open at a differential greater than 2 psid (pounds per square inch differential). If it opens at or below 2 psid, the assembly fails.

Testing Check Valve 1 (CV1)

With the kit connected across test cocks 2 and 3:

1. Slowly close the downstream shutoff valve (No. 5 test cock / outlet isolation).

2. Open the inlet fully and allow pressure to stabilize.

3. The differential pressure reading represents how tightly CV1 holds. A passing result is a positive differential that does not drop to zero — meaning Check Valve 1 is holding and not allowing reverse flow. Typical passing differentials are well above the relief valve threshold.

Testing Check Valve 2 (CV2)

Move the kit connections: high-side to test cock No. 3, low-side to test cock No. 4 (downstream of CV2, upstream of the outlet shutoff). Repeat the isolation and stabilization steps. CV2 must also hold a positive differential; if the reading bleeds to zero, CV2 is fouled or damaged.

Reading Failure Modes

| Symptom on Gauge | Failure Mode |

|---|---|

| Relief valve opens at or below 2 psid | DPRV failed (spring weak or seat fouled) |

| CV1 differential bleeds to zero | CV1 fouled or check disc damaged |

| CV2 differential bleeds to zero | CV2 fouled or check disc damaged |

| Continuous discharge from vent at normal flow | DPRV or CV1 failed together |

When a failure is found, document it on the standard field test report form: record the actual differential reading, the failing component, and the recommended corrective action (typically: repair or replace the assembly, and notify the water purveyor or authority having jurisdiction before returning the assembly to service).

Completing the Field Test Report Form

Fill in every field: site address, assembly make/model/serial number, date, test kit serial number and calibration date, test cock numbers used, each differential reading, pass/fail for each component, and your printed name and certification number. An incomplete form is not acceptable for ASSE certification documentation. Sign only after all readings are recorded — altering readings after the fact is a professional and potentially legal violation.

Key terms8

Differential pressure (psid)The difference in pressure between two measurement points, expressed in pounds per square inch differential; the fundamental measurement in RPZ field testing.
Reduced-pressure zone (RPZ)The low-pressure chamber between Check Valve 1 and Check Valve 2 in an RPZ assembly; maintained at a pressure lower than supply to ensure the relief valve can open before backflow occurs.
Differential pressure relief valve (DPRV)The hydraulically operated valve inside an RPZ assembly that vents to atmosphere when the zone pressure approaches supply pressure, preventing backflow.
Check valve (CV1 / CV2)A spring-loaded one-way valve inside the RPZ assembly; CV1 is on the upstream side and CV2 is on the downstream side; both must hold a positive differential to pass.
Calibrated test kitA differential-pressure gauge instrument with connecting hoses and needle valves used to measure pressure differentials across RPZ components; must be within its calibration interval for readings to be valid.
Test cockA small shutoff port built into the RPZ assembly body that allows the test kit hoses to be connected without removing the assembly from the line.
Opening pointThe differential pressure at which the relief valve first discharges water; must be above 2 psid for a passing result.
Authority having jurisdiction (AHJ)The governmental body or agency that enforces plumbing and backflow codes in a given locality; establishes test frequency and documentation requirements.

Worked examples4

1. During the relief valve opening-point test, the technician records that the DPRV first opens when the gauge reads 1.8 psid. Does the assembly pass or fail this portion of the test?
  1. Recall the passing criterion: the relief valve must open at a differential greater than 2 psid.
  2. Compare the recorded reading: 1.8 psid is less than 2 psid.
  3. Conclusion: the opening point is below the minimum threshold.
Answer: FAIL. The relief valve opened at 1.8 psid, which does not meet the minimum of greater than 2 psid. Document the actual reading, note the DPRV as the failed component, and recommend repair or replacement.
2. The technician tests CV1 and records an initial differential of 5.2 psid. After 30 seconds the reading has bled down to 0.0 psid. What does this indicate, and what should be recorded?
  1. A differential that bleeds to zero means the check valve is not holding — pressure has equalized across it, indicating reverse flow past the check disc.
  2. A passing check valve maintains a positive differential (does not reach zero).
  3. Since the reading reached 0.0 psid, CV1 has failed to hold.
Answer: FAIL on CV1. The check valve disc is fouled or damaged. Record the initial reading (5.2 psid), the final reading (0.0 psid), mark CV1 as failed, and recommend repair or replacement of the assembly before return to service.
3. A technician tests CV2 and records a steady differential of 3.4 psid that does not change over the observation period. Separately, the relief valve opened at 4.1 psid. What is the overall status of the assembly for these two tests?
  1. CV2: 3.4 psid is positive and held steady — this is a passing result for CV2.
  2. Relief valve opening point: 4.1 psid is greater than the required 2 psid — this is a passing result for the DPRV.
  3. Both components tested here pass their respective criteria.
Answer: Both tests PASS. CV2 held a positive differential of 3.4 psid, and the relief valve opened at 4.1 psid, which exceeds the 2 psid minimum. Record both readings with a PASS designation on the field test form.
4. The test kit high-side reads 14.0 psid and the low-side reads 9.5 psid when connected across CV1. What is the differential across CV1?
  1. Differential = high-side pressure − low-side pressure.
  2. Differential = 14.0 psid − 9.5 psid = 4.5 psid.
  3. Compare to criterion: 4.5 psid is positive and above zero, so this check valve is holding.
Answer: The differential across CV1 is 4.5 psid — a passing result, provided the reading remains stable and does not bleed to zero during the observation period.
In class: Instructor demo: connect test kit to RPZ test cocks in correct order, demonstrate differential pressure reading across the relief valve, and explain the minimum acceptable differential for a passing result · Guided practice: learners work through each stage of the RPZ test procedure in pairs, with one learner operating the kit and one recording readings; roles swap for a second test · Failure-mode exercise: instructor pre-sets training-rig RPZs with deliberate faults (fouled check, failed relief valve); learners run the test, identify the failure mode from readings, and document recommended corrective action on the form
Materials: Calibrated differential-pressure gauge test kits; RPZ assemblies on training rigs (normal and pre-faulted); ASSE 5013 field test procedure; standard field test report forms; instructor-prepared fault condition documentation
Check: Failure-mode exercise: learner correctly identifies fault type from differential pressure readings in at least 3 of 4 pre-set scenarios (75%) and documents a corrective action for each; form completion 100%

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

ASSE Backflow field testing procedures
1. What is the minimum differential pressure at which the relief valve of an RPZ assembly must open in order to achieve a passing result?
ASSE Backflow field testing procedures
2. During an RPZ field test, the CV1 differential reading starts at 4.8 psid and slowly bleeds down to 0.0 psid. This result indicates:
ASSE Backflow test equipment
3. Why is it critical that a test kit be within its calibration interval before performing an RPZ field test?
ASSE Backflow field testing procedures
4. During an RPZ field test, which test cocks should the high-side and low-side hoses be connected to when testing the differential across Check Valve 1?
ASSE Backflow failure analysis
5. A technician observes continuous water discharging from the RPZ relief valve vent port during normal supply flow conditions before any test cocks are opened. This most likely indicates:
ASSE Backflow documentation
6. Which of the following is required on a completed RPZ field test report form for ASSE documentation purposes?
ASSE Backflow safety and test kit operation
7. When connecting the test kit hoses to the RPZ assembly, all needle valves on the kit should be:
ASSE Backflow field testing procedures
8. A technician tests CV2 on an RPZ assembly and records a steady differential of 3.1 psid that does not bleed down over the observation period. Separately, the relief valve is found to open at 1.6 psid. What is the overall assessment?
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