Check Valve Passing in Reverse / Back Leakage
A check valve that allows reverse flow in the closed position defeats its purpose as a non-return device. This can cause pump damage, product contamination, or loss of system pressure.
Symptoms
Root Causes
Worn or damaged disc seating face
The disc face and body seat ring have worn to the point where metal-to-metal contact is insufficient to prevent leakage, or soft inserts have been damaged.
Debris on seating face
Scale, weld spatter, or solid particles trapped between the disc and seat prevent full closure.
Disc not reaching the seat
A bent hinge arm, corrosion locking the pivot, or spring failure prevents the disc from traveling to its full closed position.
Disc or seat insert corrosion
Corrosion or erosion has created pits on the seating surfaces that cannot seal even with correct disc-seat contact.
Safety Precautions
- Full LOTO from both upstream and downstream before disassembly
- Drain valve and confirm zero residual pressure before opening any joint
Tools Required
- Torque wrench
- Lapping plate and compound
- Valve seat insert removal tools (manufacturer-specific)
Supplies Needed
- Replacement disc and seat insert kit (OEM part)
- Lapping compound
- Replacement hinge pin and bushing (if worn)
Step-by-Step Repair Guide
- 1
Check for debris obstruction in the seat area
Isolate and depressurise the valve. Remove the access bolting and inspect the disc and seat with a torch. Flush out any visible debris. This is the most common and simplest cause of check valve back-leakage. Scale, weld spatter from nearby field welds, and pipe mill scale are frequent culprits. After cleaning, test for leakage.
- 2
Inspect disc and seat seating faces
With the valve open, inspect the disc seating face and body seat ring (in swing check and nozzle check) or the disc plates and seat ring (in dual-plate check). Look for: circumferential grooves or pits on the metal seat, damaged or missing soft seat inserts, bent or cracked disc, elongated hinge pin hole (indicating previous chattering damage).
- 3
Lap or replace disc and seat
Light surface corrosion and minor scratches: lap the disc and seat using lapping compound (as described in gate valve seat repair procedure). Fit the disc to the body, apply compound, and rotate the disc against the seat in a back-and-forth motion. For nozzle check valves with replaceable seat inserts: replace inserts per manufacturer procedure. For dual-plate check valves: replace the spring set and disc plates as a kit.
- 4
Test seat tightness
Apply rated reverse pressure (from downstream side) and test for leakage at the upstream flange or through a body test port. Accept to API 598 Rate D or better for metal seats, zero leakage for soft-seat designs. Document and return to service.
When to Replace Instead of Repair
Replace the complete valve when body seating surfaces are corroded beyond lapping depth, or when the hinge pin bore is worn oversize and cannot be repaired.
Applicable Standards
Specification for Pipeline and Piping Valves
API 6D is the most widely cited standard for pipeline and piping valves in the oil and gas industry.
Valve Inspection and Testing
API 598 is the universal valve testing and inspection standard, defining acceptable leakage rates (leak classes) for hydrostatic shell tests, seat leakage tests, and backseat tests.
Related Products
Key Terms Explained
Unfamiliar with any terms used in this guide? Each links to a full engineering definition.
Full valve glossary (113 terms)Steps
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