1. Scope and Purpose

This manual covers maintenance and testing procedures for all types of relief valves (SPVs) (spring loaded, pilot operated) used in industrial systems to protect equipment and personnel from overpressure. Testing of VCs is critical to ensure their reliable operation and compliance with safety standards. Maintenance and testing should be performed regularly according to the recommended schedule, or after any event that may affect the integrity or functionality of the valve.

This document is intended for use by qualified service technicians, reliability engineers and process safety personnel experienced with pressure equipment.

2. Security measures

⚠ WARNING: Working with relief valves involves high pressure and potentially hazardous environments. Failure to follow procedures can result in serious injury or death.

LOCKOUT/TAGOUT (LOTO): Always use lockout/tagout (LOTO) procedures to isolate the valve from all energy sources (pressure, electricity) before starting any work. Make sure the system is completely depressurized and pressure is reduced to atmospheric.

PERSONAL PROTECTIVE EQUIPMENT (PPE): Be sure to use appropriate PPE: safety glasses or a face shield, protective gloves (chemical resistant, heat resistant - depending on the environment), protective shoes, protective clothing. When working with noise, use hearing protection.

HAZARDOUS ENERGY: Be aware of the risks associated with high pressure, high temperature, chemically aggressive or flammable environments. Check the valve data sheet and system specifications.

WORK AT HEIGHT: If work is carried out at height, use appropriate means of access (platforms, scaffolding) and safety systems.

GAS ENVIRONMENT CHECK: When working in confined spaces or in the presence of potentially hazardous gases, conduct an analysis of the gas environment.

3. Necessary Tools and Materials

Name of Tool/Material	Specification	Quantity
Kit for testing ZK	Portable or stationary stand with the possibility of supplying test pressure up to 700 bar, with a manometer scale of class 0.25 (ISO 1000/EN 837-1)	1
Manometers are calibrated	The range corresponding to the trigger pressure of ZK + 20%, the accuracy class is not lower than 0.25 (DSTU EN 837-1:2018)	2-3 (various ranges)
Wrench/socket set	Metric, from 10 mm to 60 mm	1 set
Torque wrench	Range 20-200 Nm, with calibration certificate	1
Screwdrivers (flat, Phillips)	Different sizes	1 set
A set of hexagons (hex keys)	Metric	1 set
Means for cleaning	Washing solution, brushes (brass/nylon)	As needed
Rags are clean, lint-free		As needed
Lubricant for seals	Compatible with the working environment and materials of the ZK (for example, silicone for oxygen, PTFE for aggressive)	As needed
A set of seals and gaskets	Original spare parts or certified analogues for a specific ZK model	Depending on the repair
Soap solution (or leak detector)	For visual detection of leaks	As needed
Metal ruler/caliper	To measure clearances/dimensions	1
Marker	Water resistant	1
Labels for marking		As needed

4. Checklist Before Maintenance

Item	Verification	Acceptance/Rejection Criteria	Notes
1. Documentation	Check the availability of the ZK passport, manufacturer's instructions, service history.	Passport data correspond to the actual valve, there are records of previous tests.	Deficiency: Missing or inconsistent documentation - valve identification or archival data search may be required.
2. Isolation of ZK	Confirm that the AC is isolated from the system, pressure is relieved, LOTO is applied.	The manometer on the isolated area shows 0 bar. LOTO tags are set.
3. External Review	Inspect the housing, connections, and drainage line for visible damage, corrosion, leaks, and foreign objects.	Absence of cracks, deformations, significant corrosion, icing, drips. All bolted connections are tightly tightened.	Deviation: detection of defects - conduct a detailed investigation and eliminate.
4. Marking	Check the clarity of the factory markings (manufacturer, model, serial number, operating pressure, case material).	Marking is clear, corresponds to the documentation.	Deviation: unreadable marking - use other identification methods.
5. Inlet and Outlet Pipes	Inspect the nozzles for contamination, blockages, and damage.	The nozzles are clean, free of obstructions.	Deviation: contamination – clean before disassembly.

5. Step-by-step Procedure

5.1. Dismantling the Safety Valve

Confirm isolation: Double-check that the ZK is completely isolated from the working system and the pressure is reduced to 0 bar. Remove all LOTO tags except those indicating general isolation of the site.
A common mistake: underestimating the residual pressure in the system, which can lead to an uncontrolled release of medium.
Disconnecting the drain line: If present, disconnect the drain line from the ZK outlet. Make sure there is no residual pressure in the drain.
Unscrew the fasteners: Carefully unscrew the bolts or studs securing the ZK to the system. Use the appropriate wrenches. Start with the bottom bolt and work diagonally, gradually loosening all fasteners.
A common mistake: suddenly unscrewing the fasteners - this can lead to deformation of the flanges or damage to the gaskets.
Remove the ZK: Carefully remove the relief valve from the system. ⚠ BE CAREFUL: The valve can be heavy. Use the lifting mechanisms if necessary. Move it to the test stand.

5.2. Visual Inspection and Inspection at the Stand

Cleaning: Thoroughly clean the external surfaces of the ZK from dirt, corrosion, product residues. Use appropriate cleaners and brushes.
Valve disassembly: Remove the cover and spring. Carefully disassemble the valve, fixing the position of all parts. Pay attention to the marking of the spring.
Inspect internal components:
- Plate (disc) and saddle: Inspect for scratches, erosion, corrosion, wear. Check for wear. Any defects on the sealing surfaces can lead to leaks. If damage is found, carry out mechanical lapping or replacement of damaged parts. The gap between the plate and the rod guide should not exceed 0.05-0.15 mm (for most industrial ZK), which is checked with a feeler gauge.
- Rod: Check for straightness, absence of burrs, corrosion.
- Spring: Inspect for corrosion, deformation, cracks. Compare the spring markings with the documentation. A worn or deformed spring can change the actuation pressure.
- Guide elements: Check for wear, contamination.
- Sealing: Inspect all seals (rings, gaskets) for wear, cracks, loss of elasticity. Always replace seals during disassembly, even if they look good.
Component Cleaning: Thoroughly clean all internal components using a flushing solution compatible with the valve materials and operating environment. Dry with a clean, lint-free material.
To assemble the valve: Assemble the valve in reverse order. Lubricate the new seals with the appropriate lubricant. Tighten the body bolts with a torque wrench, following the manufacturer's tightening torques (typical values for DN50 flange connections: M16 – 120-150 Nm, M20 – 240-280 Nm). Even tightening is critical for tightness.

5.3. Checking the Set Pressure

Installation on the test stand: Install the assembled ZK on the test stand. Make sure that all connections are secure and tight.
Connecting pressure gauges: Connect a calibrated pressure gauge (class 0.25) to the inlet port of the valve. The gauge range should be approximately 20% above the expected operating pressure.
Test Pressure Supply: Slowly supply the test medium (usually air or nitrogen for gas systems, water/oil for liquid systems) to the ZK inlet. The rate of pressure increase should not exceed 1 bar/sec when approaching the actuation pressure.
Fixing the actuation pressure: Keep a close eye on the pressure gauge. Record the pressure at which the valve opens and the test medium exits.
Visual indicator: a clear, sharp opening of the valve, accompanied by a characteristic noise (for gas systems) or a jet of liquid.
Common mistake: too fast pressure increase - can lead to an inaccurate determination of the actuation pressure.
Retest: Do 3-5 trials. The average value of the actuation pressure should be within ±3% of the set value for most industrial ZK (according to ISO 4126-1 or DSTU ISO 4126-1:2018). If the value is outside these limits, adjust the adjusting screw (for spring-loaded ZK) and repeat the test. Turning the adjusting screw clockwise increases the actuation pressure, counter-clockwise decreases it. Each full revolution of the screw usually changes the pressure by 0.5-2 bar, depending on the model.

5.4. Leak Testing

Pressure reduction: After checking the actuation pressure, reduce the pressure to 10-15% below the actuation pressure. This is the pressure at which the valve must be sealed.
Checking for leaks:
- For gas valves: Apply a soap solution or a special leak detector to the valve outlet and around the sealing surfaces. Visual indicator: no bubbles for 1 minute indicates tightness.
- For liquid ZK: Check the outlet nozzle for drops or jets of liquid. No more than 1-2 drops/min is allowed for small valves; for larger valves, refer to manufacturer's specifications (e.g. API 527).
Common mistake: not enough time to observe leaks or using inappropriate detection tools.
Fix leaks: If leaks are found, disassemble the valve, re-inspect the plate and seat, replace the seals, clean the sealing surfaces, then reassemble and repeat the test.

5.5. Re-certification and Marking

Completing the documentation: Fill out the test report, indicating: serial number of the ZK, operating pressure (before and after adjustment), leak test results, test date, technician's name, next scheduled test date.
Marking: Put a seal (if provided) and a tag/label with the test date and the next inspection date on the CK. This is mandatory for certification according to the UkrSEPRO standard.
Certification: ZKs that have successfully passed the tests are considered recertified and suitable for further operation. Keep all test reports as part of your service history.

6. Checklist After Maintenance

Testing/Checking	Expected Result	Actual	Skip/Reject
1. Trigger pressure	Within ±3% of the specified (according to ISO 4126-1)
2. Hermeticity (gas)	Absence of bubbles for 1 minute at a pressure 10-15% below the trigger
3. Hermeticity (liquid)	No more than 1-2 drops/min (or according to API 527)
4. Absence of external sources	Connections and housing of the ZK are dry, without traces of leaks
5. Marking and sealing	Presence of a tag with the date of the test, sealing (if required)
6. Documentation	The test report is filled out and signed

7. Troubleshooting Guide

Symptom	Probable Cause	Corrective Action
The control valve does not activate at the specified pressure (the activation pressure is too high)	Excessive spring precompression Corrosion or contamination that prevents the plate from moving Wrong spring	Reduce the pre-compression of the spring with the adjusting screw Disassemble, clean, check moving parts Check and replace spring according to specification
ZK is triggered below the set pressure (trigger pressure is too low)	Insufficient pre-compression of the spring Spring damage or fatigue The presence of foreign objects between the plate and the saddle	Increase the pre-compression of the spring with the adjusting screw Replace the spring Disassemble, clean the sealing surfaces
ZK "leaks" (leak) before triggering	Damage or contamination of the sealing surfaces of the plate/seat Damage or wear of seals Incorrect tightening of body bolts System vibration	Disassemble, clean, grind the plate/saddle Replace all seals Check the torque of the body bolts with a torque wrench Check sources of vibration in the system
ZK "rattles" or does not close completely after triggering	Incorrect back pressure setting Stem/guides damaged or contaminated Contamination in the drainage line	Check and adjust back pressure (for pilot ZK) Disassemble, clean, replace damaged parts Clean the drain line

8. Recommended Maintenance Schedule

Task	Frequency	Estimated Duration	Qualification Level
Visual inspection (without disassembly)	Quarterly	15-30 minutes	Operator/Technician
On-site actuation pressure test (if applicable)	Once every 1-2 years	1-2 hours	Qualified technician
Full testing and re-certification (disassembly, disassembly, testing)	Once every 3-5 years (or according to the recommendations of the manufacturer/normatives)	4-8 hours	Certified specialist
Overhaul/Replacement of components	As needed or when significant defects are detected	8+ hours	Certified specialist

9. Directory of Spare Parts

The use of original or certified replacement parts is critical to ensure the reliability and durability of relief valves.

Description Details	Typical Specification	Category UNITEC
A set of seals for ZK	Material: NBR, EPDM, Viton, PTFE (depending on the environment); size according to the ZK model	Seals and Gaskets
Spring for ZK	Material: stainless steel; stiffness class and size according to model and operating pressure	Springs
Plate (disc) ZK	Material: stainless steel, bronze, special alloys; size according to the ZK model	Valve spare parts
ZK saddle	Material: stainless steel, stellite, special alloys; size according to the ZK model	Valve spare parts
Bolts/Studs and Nuts	Material: A2, A4 (stainless steel) or steel 8.8, 10.9; metric threads M10-M30	Fastening
Gaskets are flanged	Material: graphite, rubber, PTFE (depending on temperature/pressure/environment); size DN15-DN200	Seals and Gaskets

To order and select the necessary spare parts, please visit our unitec-D electronic catalog.

10. Links

DSTU EN ISO 4126-1:2018 (EN ISO 4126-1:2013, IDT) Safety devices for protection against excessive pressure. Part 1. Safety valves.
DSTU EN 837-1:2018 (EN 837-1:1996, IDT) Manometers. General requirements and test methods. Part 1. Manometers with a round scale.
API Recommended Practice 520 (Sizing, Selection, and Installation of Pressure-Relieving Devices)
API Recommended Practice 521 (Guide for Pressure-Relieving and Depressuring Systems)
API Standard 527 (Seat Tightness of Pressure Relief Valves)
Safety valve manufacturers' operating and maintenance instructions (eg, Farris, Leser, Emerson).
National and local regulatory documents regarding the operation of pressure equipment.