The Valves Lose Its Temper, Do You Know Why?

- Sep 06, 2019-





Material selection:

GS-C251.0619,WCB.WCC,LCB,LCC,LC3,4C,4D,WC6,C5,C12, C12A,CA15CF3,CF8(-196’C),CF3M,CF8M,CF8C,CD4MCu,CK3MC   uN,ZG200-400,ZG230-450,ZG270-500,2G40Cr1,ZG20CrM0.2G15C   r1Mo1V,ZG35Cr1MO.ZG16CrMOG(1Cr5Mo),ZG1Cr13,ZGOCr18Ni9 Ti.5A.KmTB   Cr26.4A




Resin sand casting, etc.

The cause of issues

● The filler is not selected correctly, and it is not compatible with the corrosiveness, temperature and pressure of the working medium.

● The packing is not installed correctly, especially the whole packing is placed in the spare rotation, which is the most likely to cause leakage.

● The filler has exceeded the service life, has aged, and loses its elasticity.

● The number of packing turns is insufficient.

●The stem processing accuracy or surface finish is not enough, or it has ovality or nick.

● Improper operation and excessive force.

Maintenance methods

● The material and type of packing should be selected according to the working conditions.

● Fill in the shake, the packing should be placed in a circle and the joint should be 30° or 45°.

● The aging and damaged packing should be replaced in time.

● The packing should be installed according to the specified number of turns.

● Obey the operating procedures, except for the impact handwheel, operate at a constant speed and normal force.

● The gland bolts should be tightened evenly and symmetrically.

Leakage at the gasket

The reasons

●The gasket is not resistant to corrosion, high pressure, vacuum, high temperature or low temperature.

● The operation is not stable, causing the valve pressure and temperature to fluctuate up and down.

●The pressing force of the gasket is not enough.

●The gasket is improperly assembled and the force is uneven.

●The surface of the gasket is rough and foreign matter is mixed.

Maintenance method

● The material of the gasket should be selected according to the working conditions.

● Careful adjustment and smooth operation.

● Tighten the bolts evenly and symmetrically.

● The gasket assembly should be evenly stressed. The gaskets are not allowed to be overlapped and double gaskets are used.

● Pay attention to cleaning when installing the gasket, and clean the sealing surface with kerosene.

Leakage at the sealing surface

Butterfly valve

The reasons

●The sealing surface is not well ground and cannot form a tight line.

● The center of the joint between the valve stem and the closing member is suspended, not worn or worn.

● The stem is bent or misaligned, causing the closure to be skewed.

●The sealing surface material is improperly selected, and the sealing surface is corroded, washed and worn.

● Surfacing and heat treatment are not operated according to the regulations, resulting in wear, corrosion, cracks, etc.

● The sealing surface is peeled off.

Maintenance methods

●When the sealing surface is ground, the lap and abrasive are selected reasonably, and the coloring is checked after grinding. The sealing surface has no defects such as indentation, cracks and scratches.

● If the top of the joint between the valve stem and the closing member does not meet the requirements, it should be trimmed. The top center should have a certain clearance. The axial clearance between the stem shoulder and the closing member is not less than 2 mm.

● Straighten the curved valve stem, adjust the valve stem, stem nut, closure, and seat on a common axis.

●Select sealing surfaces that are resistant to corrosion, scratches, etc., in accordance with working conditions.

●High temperature valve, after closing, shrink and shrink, and close again after closing for a certain time.

●The valve used for the shut-off valve is not allowed to be used as the throttle valve or the pressure reducing valve. The closing member should be in the fully open or fully closed position. If the medium flow and pressure need to be adjusted, the throttle valve and the decompression should be separately set. valve.

● Sealing surface that cannot be adjusted and replaced in time.

stainless steel Check valve

Closed part fall off

The reasons

● Poor operation, the closing piece is stuck or exceeds the top dead center, and the joint is damaged and broken.

●The closing piece is not firmly connected and loose.

●The material of the connecting piece is not correct, and it cannot withstand the corrosion of the medium and mechanical wear.

Maintenance methods

● To operate correctly, the valve should not be used too much, and the opening valve should not exceed the top dead center. After the valve is fully opened, the handwheel should be reversed a little.

● The closing piece should be connected to the valve stem correctly and firmly, and the threaded joint should have a retaining piece.

●The fasteners used to connect the closing piece to the valve stem should withstand the corrosion of the medium and have certain mechanical strength and wear resistance. Although the closing piece is not rare, it is a very dangerous fault.

Valve stem is not flexible

The reason

●The valve rod and its matching parts have low processing precision and the matching clearance is too small.

● The axis of the valve stem, stem nut, bracket, gland, packing, etc. are not in a straight line.

● The packing is too tight.

●The valve stem is bent and damaged.

●The thread is not clean or rusted, and the lubrication condition is poor.

●The nut is loose and the thread is slippery.

● The connection between the valve stem and the transmission is loose or damaged.

Maintenance methods

● Improve the machining accuracy and repair quality of the valve stem, stem nut, etc., make sure the interval space is appropriate.

●When assembling the valve stem and its connecting parts, the gap is consistent, concentric, and flexible.

● The packing is pressed too tightly and the gland is properly loosened.

●The valve stem should be corrected for bending. If it is difficult to correct, it should be replaced. When operating the valve stem, the closing force is appropriate.

● The thread of the stem and stem nut should be cleaned and lubricated frequently. For high temperature valves, the disulfide pin or graphite powder should be applied for lubrication.

●The stem nut should be loosened and repaired. It cannot be repaired and replaced in time.

● Make the oil passage at the nut smooth, well-lubricated, infrequently operated valves, regularly check and move the valve stem, find wear and seizure, and repair the stem nut, bracket and other accessories in time.

● To operate the valve correctly, the closing force should be appropriate to avoid deformation and damage of the valve stem.

●After closing, when the valve member is heated and stretched, after the valve is closed, the valve wheel should be turned counterclockwise a little at a certain time to prevent the valve stem from dying.

Valve body and bonnet leakage

The reasons

●The valve body has blisters or cracks.

●The valve body is cracked during repair welding.

Maintenance methods

● Polish the suspected cracked area and etch it with 4% nitric acid solution. If there is a crack, it can be displayed.

● Excavation or replacement of cracks.

The reasons

● Spring fatigue.

●The spring is not used properly.

Maintenance methods

● Spring fatigue, no doubt should be replaced.

●The spring valve has several pressure sections, and each pressure section has a corresponding spring, such as a safety valve with a nominal pressure of 16 kg/cm2.

The pressure is 2.5 to 4 kg / cm 2 of the pressure section, installed 10 ~ 16 kg / cm 2 of the spring, although it can be made to open, but high and low, very insensitive.

The above description of common faults and maintenance methods can only be inspiring. In actual use, other faults will be encountered. To actively and flexibly prevent valve failures, the most fundamental one is to be familiar with its structure. Material and motion principle.