Safety valve test procedure: pressure setting check, leak test and re-certification

1. Scope and purpose

This practical guide covers procedures for disassembly, internal inspection, set pressure testing, leak testing and re-certification of spring-loaded relief valves (SPVs) and pilot relief valves (PLVs) used to protect industrial equipment against overpressure. Testing and maintenance of ZK is critical to ensure personnel safety, equipment integrity, and compliance with manufacturing standards. This procedure is applied to VCs working with liquids, gases and steam in the chemical, oil and gas, energy and food industries. It is recommended to test and re-certify the valve according to the preventive maintenance schedule, after any overpressure event, or if a valve malfunction is suspected.

2. Precautions

ATTENTION! Energy hazard and life hazard!

• Before starting any work with the ZK, be sure to perform the blocking/marking procedure (LOTO) in accordance with the company's internal instructions. Ensure that all sources of energy (mechanical, electrical, hydraulic, pneumatic, chemical, thermal) are isolated and blocked.
• Do not work under pressure. Make sure that the system where the ZK is installed is completely de-energized and the pressure is reduced to atmospheric.
• Use the appropriate personal protective equipment (PPE): safety glasses (DSTU EN 166:2017), protective gloves (DSTU EN 388:2017), protective clothing (DSTU EN ISO 13688:2016), protective shoes with metal toes (DSTU EN ISO 20345:2016) and hearing protection (DSTU EN 352-1:2017) when working with loud equipment or potentially explosive environments.
• Hot liquids and steam can cause serious burns. Allow valve and piping to cool completely before disassembly.
• Toxic or aggressive liquids require special PPE and handling procedures. Read the material safety data sheet (MSDS) of the fluid contained in the system.
• Use proper lifting equipment for heavy valves. Ensure that the valve is securely fastened during transport and testing.

3. Necessary tools and materials

4. Pre-repair inspection checklist

5. Step-by-step procedure

This procedure involves dismantling the ZK from the technological line for testing on a specialized stand.

1. Dismantling of the ZK from the line

   1. Isolation and LOTO: STRICTLY follow the LOTO procedure. Isolate the CC from all sources of pressure and energy. Close the shut-off valve before and after ZK.
   2. Relief of pressure: Slowly and in a controlled manner, release the residual pressure from the section of the pipeline where the ZK is installed through the drain hole. Make sure the pressure has reached atmospheric pressure. Never rush the depressurization process.
   3. Drainage: Ensure complete drainage of fluids from the valve and adjacent piping.
   4. Unscrewing the bolts: Loosen and unscrew the ZK flange bolts. Use the appropriate wrenches.
   5. ZC removal: Using lifting equipment (if the ZC is heavy), carefully remove the valve from the line. Make sure the valve is supported evenly. Avoid drops and shocks that may damage the valve's internal components.
   6. Transportation: Transport the ZK to the test site in an upright position to prevent damage to the saddle and disc.

2. External cleaning and inspection

   1. Cleaning: Thoroughly clean the external surfaces of the ZK from dirt, rust, and old seals. Use metal brushes for coarse dirt and lint-free rags with solvent for final cleaning.
   2. Detailed visual inspection: Re-inspect the body, flanges, cap, stem for cracks, deformation, corrosion damage, wear. Pay special attention to joints and welds.
   3. Nameplate check: Make sure that all data on the nameplate (setting pressure, back-off pressure, material) corresponds to the data sheet and system requirements.

3. Disassembly (for full maintenance)

   This step is performed if full maintenance, internal inspection or repair is planned. A simple check of the set pressure may not require complete disassembly.

   1. Marking: Before disassembly, mark the parts, which will allow you to assemble the valve correctly. Take a photo of the location of the components.
   2. Removing the cap/lid: Carefully unscrew the bolts securing the cap/lid.
   3. Removing the spring: Remove the adjusting washers (if any) and carefully pull out the spring. Always check the spring for corrosion, cracks, deformations.
   4. To remove the stem, disc and saddle: Carefully remove the stem, disc and saddle (if removable).
   5. Component Cleaning: Thoroughly clean each part of deposits, corrosion and foreign particles.

4. Internal inspection and pawing

   1. Inspection of internal surfaces: Inspect the internal surfaces of the valve body for corrosion, erosion, cavitation damage.
   2. Inspection of the seat and disc: Carefully inspect the working surfaces of the seat and disc for scratches, dents, corrosion damage or signs of erosion. The surfaces must be perfectly smooth.
   3. Lapping (if necessary): If the saddle and disc surfaces are damaged, perform lapping. Use lapping pastes from coarse to fine grain. Achieve a mirror-like surface and perfect flatness. Flatness can be checked using an optical flatness meter and monochromatic light (no more than 1-2 light rings are allowed). Do not allow excessive metal removal, which can alter valve geometry and performance.
   4. Inspection of the spring: Check the spring for deformation, cracks, corrosion. Measure the free length of the spring and compare with the manufacturer's data. A deformed or damaged spring must be replaced.
   5. Rod and Guide Inspection: Inspect the rod for straightness, wear, or corrosion. Inspect the guide bushings for wear. The movement of the rod must be free.

5. Collection of ZK

   1. Installing the seat and disc: Install the cleaned and sanded seat and disc.
   2. To install the rod and spring: Install the rod, spring and adjusting washers. Make sure all components are in the correct position.
   3. Screwing the cap/lid: Install a new gasket (material according to DSTU EN 1514-1:2009 for flanges) and install the cap/lid. Tighten the bolts with a torque wrench in a cross pattern according to the manufacturer's recommendations. Typical tightening torque values ​​for ANSI B16.5 flanges: for M20 bolts of class 8.8 – 200-250 Nm. Incorrect tightening torque can lead to deformation of the case, leaks or jamming of the mechanism.

6. Set pressure test (Opening pressure)

   1. Installation on the bench: Install the ZK on a certified test bench. Make sure all connections are tight.
   2. Selecting the test medium: Use the appropriate test medium: air or nitrogen for gases/vapours; water or oil for liquids. The temperature of the test environment should be in the range of 15-25°C, unless otherwise specified by the manufacturer.
   3. Pressure delivery: Apply pressure slowly and steadily to the ZK inlet. The rate of pressure increase should be no more than 1 bar/s to accurately determine the opening point.
   4. Fixing the opening pressure: Record the reading of the reference pressure gauge at the moment the disk starts to rise (visible movement of the disk or the first stable bubble for gas ZK). This is the opening pressure (set pressure).
   5. Adjustment: If the opening pressure does not correspond to the specified value (allowable deviation ±3% for ZKs conforming to DSTU EN ISO 4126-1:2018), adjust it using the ZK adjustment screw. To increase the pressure, twist it, to decrease it, unscrew it. After each adjustment, repeat the test. Do not attempt to adjust the opening pressure when the valve is under significant pressure. Always depressurize before adjusting.
   6. Retest: After reaching the required opening pressure, perform a minimum of 3 consecutive tests to ensure the stability of the setting. The difference between tests should not exceed 0.5%.

7. Definition of reseating pressure

   The back-closing pressure is the pressure at which the ZK disk returns to the seat after fully opening. This is critical to minimize product loss and avoid permanent leaks.

   1. Continuation of the test: After fully opening the valve, slowly reduce the pressure at the valve inlet.
   2. Fixing the reverse closing pressure: Record the manometer reading at the moment when the ZK disc is fully returned to the seat and the medium flow stops. This is the reverse closing pressure.
   3. Criteria: For gas valves, the reverse closing pressure is usually 80-90% of the opening pressure. For liquid ZK - 90-95% of the opening pressure. For specific values, see the ZK passport. Insufficient back-closing pressure may indicate problems with the spring or internal seals.

8. Seat Leakage Test

   A seat leak test is performed to verify the absence of leaks at the operating pressure or at a pressure close to but below the opening pressure.

   1. Pressure supply: Apply a pressure equal to 80-90% of the set pressure (according to DSTU EN ISO 4126-1:2018 and the manufacturer's requirements) to the input of the control unit. Hold this pressure for 1-5 minutes to stabilize.
   2. Test method for gases: Lower the outlet of the ZK into a measuring vessel with water or a special liquid to detect bubbles. Count the number of bubbles in one minute.
   3. Permissible leakage rates (example):
      • For a water tank with a diameter of a conditional passage up to DN50: 1-5 bubbles/min.
      • For ZK with the diameter of the conditional passage DN50-DN100: 5-10 bubbles/min.
      • For ZK with a diameter over DN100: 10-20 bubbles/min.
      • For particularly critical applications: 0 bubbles/min for 30 seconds.
      Always check the specific leakage rates in the ZK passport and relevant industry standards. Excessive leaks require re-lapping or replacement of saddle/disc components.
   4. Test Method for Liquids: Observe the flow of liquid from the outlet. Allowable leaks are usually measured in drops per minute or no visible drops. Alternatively, you can use the pressure drop method in a closed volume.

9. External tightness test

   1. Pressure supply: Apply the maximum operating pressure or opening pressure to the input of the control valve.
   2. Detecting leaks: Apply a soapy solution or a special leak detector to all external connections (flanges, threaded connections, stem insertion points). The absence of bubbles indicates tightness.

10. Documentation and recertification

    1. Completing the report: Fill out the test report, which must contain:
       • ZC data (model, serial number, DN, PN).
       • Adjusted pressure, back-closing pressure, leak test results.
       • Test date, name and signature of the responsible person.
       • Used test equipment and its calibration.
       • Conclusion on suitability for operation.
    2. Sealing: After successful testing and re-certification, the ZK adjustment screw must be sealed. Use a non-destructive seal (such as a metal wire with a plastic seal) that makes it impossible to change the set pressure without damaging it.
    3. Marking: Attach a new identification tag to the HC containing information about the test date, set pressure, act/certificate number and next test date.

11. Reinstalling the ZK on the line

    1. Preparation of flanges: Clean the pipeline flanges from old gaskets and dirt. Check the surfaces for damage.
    2. Installing a new gasket: Install a new, suitable gasket between the flanges of the ZK and the pipeline.
    3. Installation of the ZK: With the help of lifting equipment, carefully install the ZK in the design position. Align the flanges.
    4. Bolt tightening: Install the flange bolts. Tighten them with a torque wrench in a criss-cross pattern in several stages to the recommended torque. For typical values, see in paragraph 5e. Uneven tightening can lead to leaks and deformation of the flanges.
    5. Removal of LOTO: After completion of all work and inspection, remove lockout and marking of LOTO.

12. Returning the system to operation

    1. Gradual increase in pressure: Increase system pressure slowly and in a controlled manner.
    2. Check for leaks: When working pressure is reached, check all connections for leaks using a soapy solution.
    3. Control of operation of the ZK: Make sure that the ZK remains airtight at the operating pressure and does not have unauthorized activations.

6. Post-repair control checklist

7. Troubleshooting guide

8. Recommended maintenance schedule

9. Directory of spare parts

Timely replacement of worn components is critical for the reliable operation of the control system. The following are typical replacement parts:

To order original spare parts or to select analogs, visit our electronic catalog UNITEC-D.

10. Links

• DSTU EN ISO 4126-1:2018 Safety devices for protection against excessive pressure. Part 1. Safety valves.
• DSTU EN ISO 13688:2016 Protective clothing. General requirements.
• DSTU EN 166:2017 Means of individual eye protection. General technical requirements.
• DSTU EN 388:2017 Protective gloves against mechanical risks.
• DSTU EN 352-1:2017 Means of individual protection of hearing organs. Headphone.
• DSTU EN ISO 20345:2016 Personal protective equipment. Protective shoes.
• DSTU EN ISO 6789:2019 Torque wrenches and screwdrivers.
• DSTU EN 1514-1:2009 Flanges and their connections. Types of gaskets for pipe flanges. Part 1. Non-metallic flat gaskets with sealing rims.
• Valve Manufacturer's (OEM) Operation and Maintenance Manual.
• Internal instructions of the enterprise on labor protection and LOTO.