1. Preparation work
Safety measures and medium draining
Close the valve and cut off the medium supply, drain the residual medium in the pipeline, and ensure a safe operating environment; Prepare tools: flange wrench, special seal removal tool (such as non-metallic pry bar), cleaning agent (alcohol or acetone), new seal (matching the working conditions such as EPDM, NBR or metal seal).
Valve disassembly
Loosen the double flange connection bolts and remove the butterfly valve from the pipeline as a whole to avoid damaging the flange sealing surface by forced disassembly; If only the valve seat seal is replaced, only the upper half of the valve body can be removed (depending on the valve structure design).
2. Seal replacement steps
Remove the old seal assembly
Soft seal: Use a non-metallic tool (plastic pry bar) to pry out the old seal evenly along the edge of the valve seat to avoid scratching the valve body or butterfly plate surface; Hard seal valve seat: Remove the fixing bolts or retaining rings, separate the metal seal and the valve body, and use heating to soften the adhesion if necessary. Cleaning and Inspection
Remove the residual colloid, rust and impurities in the valve seat groove, and use fine sandpaper (600 mesh or above) to grind the sealing surface until it is flat and smooth;
Check whether there are cracks or deformations in the valve body sealing groove. For hard-sealed butterfly valves, check whether the contact surface between the butterfly plate and the valve seat is evenly worn.
Install new seals
Soft seal ring:
Soak the new seal ring in warm water (about 50℃) to soften it, and press it evenly into the valve seat groove to ensure that there is no twisting or folding;
Some designs require the use of special pressing tools (such as rubber sleeve guides) to align the seal ring with the valve body hole and then press it to fix it.
Hard-sealed valve seat:
Apply high-temperature grease to the metal seal ring, insert it into the valve seat groove, and fix it with bolts or retaining rings. Check whether the contact line between the butterfly plate and the sealing surface is continuous and uninterrupted.
3. Reassembly and commissioning
Valve assembly
Install the butterfly plate into the valve body, ensure that the valve stem and butterfly plate are tightly connected, and apply silicone-based grease to the valve stem seal;
Tighten the flange bolts in diagonal order to reach the torque value recommended by the manufacturer (such as about 120-150N·m for DN200 valve).
Sealing test
Perform a low-pressure water pressure test (1.25 times the working pressure), maintain the pressure for 5 minutes, and observe whether there is leakage at the flange interface and valve stem;
Hard-sealed butterfly valves can detect microscopic leakage on the sealing surface through fluorescent penetrants.
4. Precautions
Seal directionality: Some bidirectional sealed butterfly valves need to distinguish the flow direction of the medium. When installing, confirm that the direction of the sealing ring is consistent with the direction of the medium pressure;
Cleaning requirements: It is forbidden to wipe rubber seals with oily rags to avoid accelerated aging;
Spare parts matching: Replacement seals must be consistent with the original specifications to avoid seal failure due to dimensional deviation.
