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2021

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01

Solution to regulating valve leakage

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For valves that do not use sealing grease, consider adding sealing grease to improve the valve stem sealing performance.

 

Add sealing grease method

 

For valves that do not use sealing grease, consider adding sealing grease to improve the valve stem sealing performance.

 

Add filler method

 

In order to improve the sealing performance of the packing to the valve stem, the method of adding packing can be used. Usually, double-layer or multi-layer mixed fillers are used. Simply increasing the quantity, such as increasing the number from 3 pieces to 5 pieces, will not have obvious effect.

 

Replacing graphite filler method

 

 

 

The widely used PTFE packing has an operating temperature in the range of -20 to +200°C. When the temperature changes greatly between the upper and lower limits, its sealing performance will significantly decrease, it will age quickly and its life will be short.

Flexible graphite fillers overcome these shortcomings and have a long service life. Therefore, some factories have changed all the PTFE packing to graphite packing, and even the newly purchased control valves have been used after replacing the PTFE packing with graphite packing. However, the hysteresis of using graphite filler is large, and sometimes crawling occurs at first, so some consideration must be given to this.

 

Change the flow direction and place P2 at the valve stem end.

 

When △P is large and P1 is large, sealing P1 is obviously more difficult than sealing P2. Therefore, the flow direction can be changed from P1 at the valve stem end to P2 at the valve stem end, which is more effective for valves with high pressure and large pressure difference. For example, bellows valves should usually consider sealing P2.

 

Lens gasket sealing method

 

For the sealing of the upper and lower covers, the sealing of the valve seat and the upper and lower valve bodies. If it is a flat seal, under high temperature and high pressure, the sealing performance is poor, causing leakage. You can use a lens gasket seal instead, which can achieve satisfactory results.

 

Replace gasket

 

So far, most sealing gaskets still use asbestos boards. At high temperatures, the sealing performance is poor and the service life is short, causing leakage. In this case, you can use spiral wound gaskets, "O" rings, etc., which many factories have now adopted.

 

Tighten the bolts symmetrically and use thin gasket sealing method

 

In the regulating valve structure with "O" ring seal, when thick gaskets with large deformation (such as winding sheets) are used, if the compression is asymmetrical and the force is asymmetrical, the seal will easily be damaged, tilted and deformed. Seriously affect the sealing performance.

Therefore, when repairing and assembling this type of valve, the compression bolts must be tightened symmetrically (note that they cannot be tightened at once). It would be better if the thick gasket can be changed to a thin gasket, which can easily reduce the inclination and ensure sealing.

 

Methods to increase the width of the sealing surface to prevent the flat valve core from beating when it is closed and reduce its leakage

 

The flat valve core (such as the valve plug of the two-position valve and sleeve valve) has no guide and guide curved surface in the valve seat. When the valve is working, the valve core is subject to lateral force and flows out from the inflow direction. Square, the larger the matching gap of the valve core, the more serious this unilateral phenomenon will be. In addition, deformation, non-concentricity, or small chamfering of the valve core sealing surface (generally 30° chamfering for guidance) will result in valve core sealing when it is close to closing. The chamfered end face is placed on the sealing surface of the valve seat, causing the valve core to jump when closing, or even not closing at all, greatly increasing valve leakage.

The simplest and most effective solution is to increase the size of the valve core sealing surface, so that the minimum diameter of the valve core end face is 1 to 5 mm smaller than the valve seat diameter, and has sufficient guidance to ensure that the valve core is guided into the valve seat and maintains Good sealing surface contact.