Solutions for leakage of high-pressure valves (6 methods)
Solutions for leakage of high-pressure valves (6 methods)
1) Adding sealing grease method For valves that do not use sealing grease, it may be considered to add sealing grease to improve the sealing performance of the valve stem.
2) The method of adding packing can be used to improve the sealing performance of the packing on the valve rod. Usually, double or multi-layer mixed fillers are used, and simply increasing the quantity, such as increasing 3 to 5 pieces, does not have a significant effect.
3) Due to the large amount of tetrafluoro fillers used in the replacement graphite packing method, their working temperature is within the range of - 20 to+200 ℃. When the temperature is within the upper and lower limits and changes greatly, their sealing performance significantly decreases, with rapid aging and short service life. Flexible graphite fillers can overcome these shortcomings and have a long service life. As a result, some factories have all changed tetrafluoro packing to graphite packing, and even newly purchased high-pressure valves have replaced the tetrafluoro packing with graphite packing for use. However, the use of graphite fillers has a large return difference, and some of them also produce creeping phenomenon at the beginning, which must be considered.
4) When P is larger and P1 is larger, sealing P1 is obviously more difficult than sealing P2 by changing the flow direction and placing P2 at the valve rod end. Therefore, the method of changing the flow direction can be adopted, changing P1 to P2 at the valve stem end, which is more effective for valves with high pressure and large differential pressure. For example, a bellows valve should generally consider sealing P2.
5) The lens gasket sealing method is used to seal the upper and lower covers, as well as the valve seat and the upper and lower valve bodies. If it is a planar seal, under high temperature and pressure, the sealing performance is poor, causing leakage. It can be replaced with a lens gasket seal, which can achieve satisfactory results.
6) Since the replacement of sealing gaskets, most sealing gaskets are still made of asbestos sheets. Under high temperatures, their sealing performance is poor and their lifespan is short, causing leakage. In this case, spiral wound gaskets, "O" rings, etc., can be used instead, and are now used in many factories.
4、 Solutions to High Pressure Valve Vibration (8 Methods)
1) The method of increasing stiffness can eliminate or weaken oscillations and slight vibrations by increasing the stiffness. For example, using a spring with large stiffness or using a piston actuator is feasible.
2) The method of increasing damping is to increase the friction against vibration. For example, the valve plug of a sleeve valve can be sealed with an "O" ring, and graphite packing with high friction can be used. This can still have a certain effect on eliminating or weakening slight vibration.
3) Increase the guide size and reduce the fit clearance. Generally, the guide size of shaft plug valves is small, and the fit clearance of all valves is generally large, ranging from 0.4 to 1mm. This is helpful for generating mechanical vibration. Therefore, when slight mechanical vibration occurs, the vibration can be reduced by increasing the guide size and reducing the fit gap.
4) "Changing the shape of the throttle element and eliminating resonance method Due to the so-called vibration source of the high-pressure valve occurring at the throttle port with high-speed flow and sharp pressure changes, changing the shape of the throttle element can change the vibration source frequency, which is relatively easy to solve when the resonance is not strong.". The specific method is to turn the valve core curved surface within the vibration opening range by 0.5~1.0mm. For example, a self operated high-pressure pressure valve was installed near the family area of a factory, and the resonance generated a howl that affected the rest of employees. After we dropped the valve core curved surface 0.5 mm, the resonance howl disappeared.
5) The method of replacing the throttle element to eliminate resonance includes:
① Change the flow characteristics, logarithmic to linear, linear to logarithmic;
② Replace the valve core form. For example, changing the shaft plug type to a "V" groove valve core, and changing the shaft plug type of a double seat valve to a sleeve type; Change the sleeve with a window to a sleeve with a small hole, etc. For example, in a nitrogen fertilizer plant, a DN25 double-seat valve often vibrates at the connection between the valve stem and the valve core. After confirming that it is resonant, we changed the linear characteristic valve core to a logarithmic valve core, and the problem was solved. Another example is a DN200 sleeve valve used in a laboratory of an aviation college, where the valve plug has a strong rotation and cannot be used. After changing the sleeve with a window to a sleeve with a small hole, the rotation immediately disappears.
6) Replace the high-pressure valve type to eliminate resonance. High pressure valves with different structural forms naturally have different natural frequencies. Changing the type of high pressure valve is the most effective method to fundamentally eliminate resonance. "A valve that resonates very strongly during use (can damage the valve in severe cases), rotates strongly (even if the valve stem is broken or twisted), and produces strong noise (up to more than 100 decibels), as long as it is replaced with a valve with a large structural difference, immediate results are achieved, and the strong resonance miraculously disappears.". For example, when a DN200 sleeve valve is selected for the new expansion project of a vinylon factory, the above three phenomena exist, causing the DN300 pipe to jump, the valve plug to rotate, and the noise to exceed 100 decibels. The resonance opening is 20-70%. Considering the large resonance opening, after switching to a double seat valve, the resonance disappears and is put into normal operation.
7) The method of reducing cavitation vibration should naturally find ways to reduce cavitation vibration caused by cavitation bubble rupture.
① The impact energy generated by bursting bubbles does not act on solid surfaces, especially the valve core, but is absorbed by the liquid. Sleeve valves have this feature, so it is possible to change the plug type valve core to a sleeve type.
② Take all measures to reduce cavitation, such as increasing throttle resistance, increasing the pressure at the choke port, and reducing pressure in stages or series.
8) Avoiding Vibration Source Wave Strike Method Valve vibration caused by external vibration source wave strikes is clearly something that should be avoided during normal operation of high-pressure valves. If this vibration occurs, corresponding measures should be taken
