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How to deal with the Control Valve Stagnation, Blockage and Leakage?

How to deal with the Control Valve Stagnation, Blockage and Leakage

Pipeline welding slag, rust, slag, etc. in the throttle port, guiding parts, under the bonnet balance hole caused by blockage or stuck so that the spool surface, guiding surface to produce strains and scratches, indentation on the sealing surface.

This often occurs in the new operation of the system and overhaul after the initial operation. This is the most common failure.

In this case, it must be unloaded for cleaning, remove the slag, such as sealing surface damage should also be ground; at the same time, the bottom plug to open, in order to flush out from the balance of the hole into the lower bonnet of the slag, and the pipeline flushing. Before commissioning, let the regulating valve fully open, the media flow for a period of time before incorporating into normal operation.

(2) External flushing method

For some easy to precipitate, containing solid particles of the media using ordinary valve regulation, often in the throttle port, guided by the clogging, can be in the bottom of the valve cover plug external flushing gas and steam. When the valve is blocked or stuck, open the external gas or steam valve, you can complete the flushing work without moving the regulator, so that the valve operates normally.

(3) Installation of pipeline filter method

For small-diameter control valve, especially the ultra-small flow control valve, the throttle gap is very small, the media can not have a little slag. In this case, the blockage, it is best to install a filter in the pipeline before the valve to ensure the smooth passage of the medium.

With the use of positioner control valve, the positioner is not working properly, the gas line throttle port blockage is the most common failure.

Therefore, with the positioner work, you must deal with the air source, usually used in the positioner before the installation of air filtration and pressure reducing valve on the gas pipeline.

(4) Increase the throttle gap method

Such as solid particles in the medium or pipeline washed out of the welding slag and rust, etc. because of the throttle port can not be caused by the blockage, stuck and other faults, can be changed to throttle clearance throttle parts – throttle area for the open window, open-ended type of spool, sleeve, because of its centralized throttle area rather than the circumferential distribution of the fault can be easily ruled out.

If it is a single, double-seated valve can be changed into a plunger-shaped spool “V” shaped spool, or into a sleeve valve. For example, a double seat valve in a certain chemical plant often gets stuck. It is recommended to replace the sleeve valve and the problem should be solved immediately..

(5) Media flushing method

The use of the medium’s own scouring energy, scouring and take away easy to precipitate, easy to block things, thereby improving the valve’s anti-blocking function. Common methods are:

① change to flow closed type use;

② the use of streamlined valve body;

③ will be placed in the throttle port of the most powerful scouring, the use of this method should pay attention to improve the ability to resist the scouring of the throttle material.

(6) Straight through to the angle method

Straight through the inverted S flow, flow path is complex, the upper and lower capacity cavity dead zone, for the media precipitation provides a place. Angle-shaped connection, the medium is like flowing through a 90 ℃ elbow, scouring performance is good, the dead zone is small, easy to design into a streamline. Therefore, the use of straight-through regulating valve produces a slight blockage can be changed to angle valve use.

(1) Increase the sealing grease method

The valve does not use sealing grease, can consider increasing the sealing grease to improve the valve stem sealing performance.

(2) Increase packing method

In order to improve the packing to the valve stem sealing performance, can be used to increase the packing method. Usually double, multi-layer mixed packing form, simply increase the number, such as 3 pieces to 5 pieces, the effect is not obvious.

(3) Replacement of graphite packing method

A large number of use of PTFE packing, because of its operating temperature in the range of -20 ~ +200 ℃, when the temperature in the upper and lower limits, changes in the larger, its sealing will be a significant decline in aging, short life. Flexible graphite packing can overcome these shortcomings and long service life. Therefore, some factories will all change the PTFE packing to graphite packing, and even the newly purchased regulating valves will be used after the PTFE packing is changed to graphite packing. However, the use of graphite packing has a large return difference, and some of them also produce crawling phenomenon at the beginning, which must be considered.

(4) Change the flow direction and set P2 at the stem end.

When △ P is larger, P1 is larger, sealing P1 is obviously more difficult than sealing P2. Therefore, can be taken to change the flow direction of the method, P1 in the stem end to P2 in the stem end, which is high pressure, differential pressure valve is more effective. Such as bellows valve should usually consider sealing P2.

(5) The use of lens pad sealing method

For the upper and lower cover seal, the valve seat and the upper and lower valve body seal. If the plane seal, at high temperatures and pressures, poor sealing, resulting in leakage, can be changed to a lens pad sealing, can get satisfactory results.

(6) Replacement of sealing gasket

So far, most of the sealing gaskets still use asbestos sheet, at high temperatures, the sealing performance is poor, the life is also short, causing leakage. In this case, can be changed to winding gasket, “O” ring, etc., now many factories have been used.

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