When the leak originates at the joint between the valve body and the pipeline flange, or between the valve body and its bonnet, the gasket is almost always the first suspect. Replacing it correctly restores the seal and prevents recurrence.PS series electric actuators,QYH641 pneumatic "O"type regulative cutting off control valve,Resistance/current valve position converter,Self-reliance electric temperature regulator,Self-reliance flow regulatorself-reliance micro-pressure regulator,Self-reliance pressure differential regulator,Self-reliance pressure regulator,Self-reliance temperature regulator,Siemens valve locator,Small flow regulating valve,Solenoid directional valve,Special seat eccentric adjustable control valve,Straight stroke electric actuatorStraight travel electronic electric actuator,Tee electric adjustable control valve,TYH968Y electric drain control valve

Confirm That the Gasket Is the Source

Before loosening any bolting, isolate the valve by closing the upstream and downstream block valves and depressurizing the line. Drain the section if the process fluid is hazardous or at elevated temperature. With the line safe, inspect the joint. Leakage that appears uniformly around the flange circumference, or that emerges from the gap between the mating surfaces, points to a failed gasket or insufficient bolt preload . Leakage concentrated at a single bolt location may instead indicate a damaged flange face or a cracked bolt, which requires a different repair path.

Prepare the Sealing Surfaces

Once the flange bolting is removed, separate the joint carefully and take out the old gasket. The critical step here is surface preparation. Both flange faces must be cleaned of all traces of the old gasket material, corrosion products, and any adhering process residue. A wire brush or a suitable scraper may be used, but the sealing surface itself must not be gouged or scratched. Any radial groove or pit on the flange face will allow the new gasket to leak regardless of how carefully it is installed. After cleaning, wipe the faces with a compatible solvent and inspect them under good light. If deep damage is found, the flange may need to be resurfaced or replaced .

Select the Correct Replacement Gasket

The replacement gasket must match the original in material, dimensions, and pressure class. Using a gasket of the wrong thickness or inner diameter can obstruct flow or fail to seat properly. For control valve body-to-bonnet joints, spiral wound gaskets with graphite or PTFE filler are common because they accommodate the thermal cycling that valves experience in service . For pipeline flange joints, the gasket material must be compatible with the process fluid and temperature. A gasket rated for the correct pressure class but the wrong temperature range will degrade prematurely. When in doubt, consult the valve manufacturer’s documentation for the specified gasket part number rather than matching by eye.

Install the New Gasket and Tighten Correctly

Place the new gasket centrally on the flange face. It should sit flat with no wrinkles or misalignment. Bring the mating flange or bonnet into position and install the bolting finger-tight. The tightening sequence matters as much as the final torque. Bolts should be tightened in a crisscross pattern, in several incremental passes, rather than fully torquing one bolt before moving to the next . This distributes the clamping force evenly and prevents the gasket from being distorted. The final torque should follow the valve manufacturer’s specification for the specific bolt size and pressure class. Under-tightening leaves the joint vulnerable to leakage under pressure, while over-tightening can crush the gasket or damage the flange faces .

Verify the Repair Before Returning to Service

After tightening, pressurize the line slowly and check the joint with a suitable leak-detection method, such as soap solution for gas service or a dry wipe for liquid service. A small initial leak that stops after a slight additional tightening may indicate that the gasket needed to settle, but a persistent leak requires the joint to be disassembled and inspected again. Do not attempt to stop a leak by over-tightening the bolts beyond specification, as this can create a hidden problem that fails later under thermal cycling. Once the joint is leak-free and the valve has been returned to normal operation, record the date and gasket material used so that future maintenance intervals can be tracked.

Do you still need to know or purchase the following control valve products:

2026-11-02

Back