Check Valve Inspection Guide: Checking Disc Wear, Pin Condition, and Seat Integrity

1. Scope and purpose

This manual covers procedures for inspection and assessment of the technical condition of non-return valves of various types (rotary, lifting, two-leaf) at industrial facilities. The goal is to identify potential failures such as disc wear, pin damage, and seal seat integrity that could lead to leaks, loss of performance, or total system failure. Regular inspection is critical to ensure reliable and safe operation of piping systems, prevent backflow and protect downstream equipment. This procedure is performed during routine maintenance, before putting new equipment into operation, or when signs of malfunction are detected, such as increased vibration, abnormal noises, or pressure drops.

2. Precautions

ATTENTION! Work with non-return valves involves the risk of injury and equipment damage. Strictly follow all safety rules.

• LOCKOUT/MARKING (LOTO): Before starting any valve disassembly or inspection work, you MUST perform the power lockout/marking (LOTO) procedure in accordance with the company's internal instructions and DSTU EN 10344:2018 (Machine Safety) standard. Make sure all power sources (mechanical, electrical, hydraulic, pneumatic) are disconnected and locked out.
• DEPRESSURE AND DRAINING: Before opening the valve, ensure that the system is completely depressurized and drained of the working medium. Ignoring this step may result in release of hazardous liquids/gases under pressure.
• PERSONAL PROTECTIVE EQUIPMENT (PPE): Use appropriate PPE: safety glasses, protective gloves (chemically resistant if working with aggressive media), safety helmet, safety shoes, protective clothing. When working in conditions of increased noise - hearing protection means.
• THERMAL HAZARDS: Be careful of hot or cold valve and piping surfaces. Use heat-resistant gloves if necessary.
• CHEMICAL RISKS: When working with aggressive chemicals, use appropriate PPE and ensure adequate ventilation.
• LIFTING OPERATIONS: When dismantling large and heavy valves or their components, use suitable lifting equipment and follow slinging rules.

3. Necessary tools and materials

Before starting work, prepare a complete set of tools and consumables.

4. Pre-repair inspection list

Perform a visual inspection and record the initial condition of the valve before disassembly.

5. Step-by-step inspection procedure

Follow each step carefully, following the specified values and criteria.

1. Preparation for inspection and dismantling

   1. System Shutdown and Power Lockout (LOTO):

      Initiate the LOTO procedure: shut down the equipment, close the stop valves before and after the non-return valve. Ventilate and dry the pipe section where the valve is installed. Failure to perform LOTO can result in fatal injury.

      Error: Incomplete depressurization of the system. Always check the absence of pressure with pressure gauges.

   2. Drainage of the working medium:

      Open the drain valves to completely remove the liquid or gas from the pipeline section. Make sure that the working medium is completely removed and there is no residual pressure. Ensure the collection of hazardous materials in appropriate containers.

      Error: Underestimation of media volume, resulting in spillage.

   3. Dismantling the flange connections:

      Mark the relative position of the valve and piping for correct reassembly. Loosen and remove the bolts/studs of the flange connections. Carefully separate the valve from the pipeline. Use suitable lifting equipment for heavy valves. Clean the flange surfaces of the pipeline from the rest of the gaskets.

      Error: Tightening the bolts "across" without gradually loosening, which can lead to deformation of the flanges.

   4. Dismantling the valve cover:

      Unscrew the bolts securing the cover to the valve body (usually this is the upper part). Keep all fasteners and gaskets in order. If the lid is stuck, use a rubber mallet to gently tap around the perimeter to avoid damaging it.

      Error: Using a metal hammer or chisel for disassembly, which can damage the sealing surfaces.

2. Inspection of internal components

   1. Disc (valve) inspection:

      Remove the valve disc. Carefully examine its surface. Signs of acceptable condition: smooth surface, without visible grooves, cracks, deep corrosion spots. Critical are:

      • Wear/Erosion: Inspect the working surface of the disc for erosive wear, especially on the edges and on the sealing surfaces. Allowable wear should not exceed 0.5 mm from the nominal thickness, unless otherwise specified by the manufacturer. Excessive wear reduces tightness.
      • Corrosion/Cavitation: Inspect for cavitation, pitting, delamination. The depth of the caverns is more than 1 mm or their large area is the basis for replacement.
      • Deformation/distortion: Check the disc for flatness using a metal ruler and feelers. Permissible distortion is no more than 0.1 mm per 100 mm of length. A curved disk will not ensure a tight fit to the saddle.

      Error: Insufficiently thorough inspection of the disk, especially its sealing surfaces.

   2. Inspection of pivot pin and bushings (for rotary valves):

      Remove the pivot pin (axle) and bushings (if present). Inspect the finger for:

      • Wear: Measure the diameter of the finger with a micrometer at several points. Permissible wear of the diameter is no more than 0.1 mm from the nominal. Wear of bushings (especially on the inside) is no more than 0.2 mm. Excessive wear leads to backlash and vibration of the disc.
      • Deformations/bends: Check finger for straightness. A bend of more than 0.05 mm is unacceptable.
      • Corrosions: Signs of intense corrosion can weaken the finger.

      Check that the disc rotates freely on your finger after cleaning. Error: Ignoring pivot backlash, which can cause seat and disc wear.

   3. Seat Inspection:

      Thoroughly inspect the seat sealing surface inside the valve body. Use an inspection mirror and a flashlight. Signs of acceptable condition: smooth, even surface, without visible defects. Critical are:

      • Erosion/wear: Presence of grooves, sinks, uneven wear. The surface must be absolutely flat and smooth to ensure tightness.
      • Corrosion/Cavitation: Indicates material incompatibility or improper operating conditions.
      • Buildings/deposits: Residues of working medium that have hardened or corrosive deposits. Delete them completely.

      Check the flatness of the saddle using a check ruler and a set of feeler gauges. The permissible gap between the ruler and the saddle should not exceed 0.05 mm. Error: Assessment of the condition of the saddle only visually, without the use of tools.

   4. Valve Body and Cap Inspection:

      Inspect the internal surfaces of the body for corrosion, erosion, cracks, foreign deposits. Check the condition of the threaded holes for attaching the cover. Inspect the sealing surfaces of the cover for damage.

3. Cleaning and assembly

   1. Component cleaning:

      Thoroughly clean all internal components (disc, pin, bushings, body, cover) from old gaskets, deposits, corrosion. Use appropriate brushes and metal cleaners. Make sure all surfaces are dry and clean before assembly.

   2. Заміна прокладок:

      ОБОВ'ЯЗКОВО використовуйте нові прокладки для кришки та фланцевих з'єднань. Це критично для забезпечення герметичності. Переконайтеся, що матеріал прокладки відповідає робочому середовищу та температурному режиму згідно DSTU EN 1514-1:2009 (Фланці та їхні з'єднання. Типи ущільнювальних поверхонь та їхнє маркування).

      Bug: Reusing old gaskets resulting in leaks.

   3. Assembling the internals:

      Install the pivot pin (with new bushings if replaced) and disc. Make sure the disc moves freely and is correctly oriented (opens in the direction of flow). Apply grease or non-stick paste to the threaded joints of the cover bolts to prevent seizing.

      Error: Incorrect disk orientation blocking thread.

   4. Valve Cover Installation:

      Install a new gasket and cover onto the valve body. Tighten the cover bolts by hand, then tighten with a torque wrench in a criss-cross pattern to ensure even pressure. Recommended tightening torques for cover bolts:

      Bolt diameter (mm)	Bolt strength class	Tightening torque (Nm)
      M10	8.8	40-50
      M12	8.8	70-80
      M16	8.8	150-180
      M20	8.8	290-320

      Refer to the valve manufacturer's documentation for exact values.

      Error: Uneven tightening, which can lead to gasket deformation or leaks.

   5. Installing the valve in the pipeline:

      Install the valve in place, orienting it according to the flow direction arrow. Install new gaskets between valve and piping flanges. Insert the bolts/studs and tighten them by hand. Then tighten with a dynamometric wrench in a cross-cross pattern in several stages to the recommended tightening torque according to the strength class of the bolts and the diameter of the flange (for example, for flanges PN16, DN100, M16 bolts of class 8.8 – 150-180 Nm).

      Error: Forgetting the flow direction arrow, resulting in incorrect valve operation.

6. List of post-repair inspections

After completing the installation and before putting the system into operation, perform functional checks.

7. Troubleshooting guide

The table lists common symptoms of check valve malfunctions, their likely causes, and corrective actions.

8. Recommended maintenance schedule

9. Directory of spare parts

To ensure uninterrupted operation, it is recommended to have a set of critical spare parts in stock. Refer to the electronic catalog of UNITEC to select and order the necessary components that comply with CE and UkrSEPRO certificates.

10. Links

• DSTU EN 12516-1:2018. Industrial pipeline fittings. Design of steel valves. Part 1: Calculation method for the strength of the hull elements.
• DSTU EN 10344:2018. Machine safety. Application of energy blocking (Lockout/Tagout).
• DSTU ISO 6789-1:2017. Manual dynamometric tools. Requirements and test methods.
• ISO 5208:2015. Industrial pipeline fittings. Pressure testing of metal valves.
• API 598. Valve Inspection and Testing (Inspection and testing of valves).
• Operating and maintenance instructions from the check valve manufacturer.