1. Leakage led by closure parts
1-1 Clause Analysis
A. poor operation make the closure parts stuck, crack and damage in connection area
B. looseness between closure parts
C. unreasonable connection parts material selection, corroded by medium and mechanical wear
1-2 Maintenance Method:
A.the force to shut down valves should not be too big; the opening extent can not exceed the max. critical point of stuck; reverse a little when valve in status of full opening level
B.the connection between disc and stem should be firm, securing ring in screwed connection
C.the fasteners for connecting disc and stem should be anti-corrosive, bear-resistance and mechanical strength.
2. Leakage in packing position
2-1 Clause Analysis
A.wrong packing selection,can’t be anti-corrosive,poor high (low) temperature resistance and high pressure resistance
B.not right packing installation,defects such as ‘replacing large unit by small ones’,uneven pressure in top and bottom area
C.over-using of packing leads to aging and no flexibility
D.Poor maching precision of shaft, defects like corrosion,wearing,bending
E.packing rings not enough and gland not pressed well
F.The damage of gland,bolts lead gland to be unable pressed well
G.the gap between gland and stem are too big and make stem abrasion,packing damaged
2-2 Maintenance Method
A.select appropriate material and style for packing basing on actual application condition
B.rightly install the packing according to O & M manual
C.check and maintenance periodically, over-aged packing should be replaced timely
D.repair the bending and abrasion stem,badly damaged ones should be changed in time
E.packing should be installed in accordance with the provisions of the number of rings, gland should be symmetrical evenly tight, gland flange sleeve should have more than 5mm preload clearance;
F.damaged gland, bolts and other parts should be promptly repaired or replaced;
G.should abide by the operating rules, in addition to impact hand wheel, valve operation at the uniform speed
H.should symmetrically tighten gland bolts, appropriately to increase the gap between gland and stem if too small; if too large, should be replaced.
3.Leakage caused by sealing surface
3-1 Clause Analysis
A.sealing surface grinding uneven, cannot form a dense line
B.there are top vacant, oblique-touch and abrasion in connection of stem and the closure parts
C.stem is bending or assembly obliquity,leading closure parts oblique and not centered.
D.material quality of the sealing surface is improper or not selected according to application conditions
3-2 Maintenance Method:
A.according to the application conditions to select right material and type of the gasket
B.symmetrically tighten bolts, if necessary, should use the torque wrench, preload force should meet the requirements, not too large or small. Flange and threaded connection should have a certain preload clearance
C.gasket assembly should be in the right, uniform force, the gasket does not allow overlapping and applying of double gaskets;
D.corrosion, damage processing, processing quality of static sealing surface is not high, should be repaired, grinded, colored inspection, make it be in line with relevant requirements;
E.pay attention to the cleaning when installation of gasket, cleaned by kerosene
4.Leakage in the junction of the sealing rings
4-1 Clause Analysis
A.the ring rolling compaction not tightly
B.bad welding quality of sealing ring and body
C.looseness of screw and insert in the sealing ring connection
D.the sealing ring connection corrded
4-2 Maintenance Method:
A.injection tackifier and then rolling fixed to the sealing ring
B.repair the sealing rings complying with welding specifications; remove the original overlaying and maching if cannot repair wedling
C.disassembly screw an insert to replace damaged parts, grinding the surface and re-assembly.
D.for the corroded sealing surface, repair by grinding method, replaced with new one if cannot repair
5.Leakage in body and bonnet
5-1 Clause Analysis
A.casting quality is not high, body and valve cover body with trachoma, loose tissue, slag and other defects
B. cold cracking phenomenon
C.bad welding, there are slag, not welding, stress cracks and other defects
D.valve are damaged by heavy impact
5-2 Maintenance Method:
A.to improve the quality of casting, in strict accordance with the provisions of shell test before installing
B.the valve applied in low temperature environment,take measures to insulate or heat tracing, the no worked valve no should get rid of water
C.for the valve with welded body and bonnet, should perform NDE test and shell test after welding work
D.no heavy objects allowed to placed on valve,no hammer allowed to hit the valve body,there should be yoke for big size valve installation
