Butterfly Valve Internal Leakage: How to Judge and Handle, Pressure Test Steps
If left untreated, internal leakage wastes fluid, upsets process control, and can erode the seat until the valve fails completely.The main Butterfly Valve product names of China Butterfly Valve Network include:Extended Hard-sealed Flange Butterfly Valve,Electric Desulfurization Wafer Butterfly Valve,Electric Desulfurization Flange Butterfly Valve,Fire Signal Butterfly Valve,Flange Soft-sealed Butterfly Valve,Flange Insulation Butterfly Valve,Flange Ceramic Hard-sealed Butterfly Valve,Flange Metal Sealed Swing Butterfly Valve,Groove Butterfly Valve.
How to Judge Internal Leakage
The first sign is often a process symptom rather than a visible leak. Downstream pressure may continue to rise after the valve is closed, or flow may not stop completely. In systems with a downstream pressure gauge, close the valve and isolate the downstream section. If the gauge pressure climbs steadily, internal leakage is present. In liquid service, listen for flow noise at the downstream pipe. In gas service, apply soapy water to the downstream drain or vent and watch for bubbles. A more definitive check is a differential pressure test. Close the valve, pressurize the upstream side to the normal operating pressure, and observe the downstream side. Any measurable pressure rise or visible flow confirms internal leakage.
Pressure Test Steps
For a formal seat leakage test, isolate the valve and install blind flanges on both sides. Fill the upstream cavity with water and vent all air. Close the valve fully. Apply the specified test pressure, usually 1.1 times the design pressure for seat tightness, or according to API 598, ISO 5208, or GB/T 13927. Hold the pressure for the required duration, typically one to five minutes depending on the standard and valve size. Observe the downstream side for leakage. A resilient seated butterfly valve should show zero leakage. A metal seated valve may allow a small allowable leakage rate according to its leakage class. Record the pressure, duration, and observed leakage.
Treatment Methods
If leakage is caused by debris trapped on the seat, open the valve slightly to create a high velocity flush, then close it again. Repeat two or three times. If the valve has an adjustable closed position stop, check that the disc reaches full contact with the seat. Adjust the stop by one or two turns and retest. Uneven flange bolt tightening can distort the body and prevent full seating, so loosen and retighten the bolts in a diagonal pattern. If the rubber seat is hardened, cracked, or extruded, replace it. If the disc sealing edge is scored, lap it lightly or replace the disc. For metal seated valves, inspect the sealing surfaces for erosion and repair by grinding only if the damage is shallow.
Summary
Internal leakage is judged by downstream pressure rise, flow noise, or a formal pressure test. The pressure test requires isolation, filling, venting, closing the valve, applying test pressure, and observing leakage against the applicable standard. Treatment begins with flushing and stop adjustment, then proceeds to seat replacement or disc repair. Correct installation and even bolt tightening prevent recurrence.
Do you still need to know or purchase the following Butterfly Valve products:
