The general valve

A.Stuffing box leakage

It is run, risk, drain the main aspects, often seen in the factory. Reasons for the leakage generated stuffing the following points: ① filler and corrosive working medium, temperature, pressure incompatible; ② filling the wrong way, especially screwed into the back fill the entire root, the most prone to leakage; ③ stem or surface finish machining accuracy is not enough, or ellipse, or nicks; ④ stem pitting has occurred, or because of the lack of protection and rust open; ⑤ stem bending; ⑥ fillers used for too long has deteriorated. 7, the operation is too fierce.

B.Off pieces leak

Stuffing box leakage is usually called the leak, the leak off pieces called internal leakage, closure of parts leak in the valve inside, not Discovery.

Off pieces leakage can be divided into two categories; a class is sealed surface leakage（Shown in Figure ）

Another is the root seal leakage（Shown in Figure ）

Cause leakage reasons: 1>, the sealing surface grinding badly; 2>, seals and valve seat, the valve do not meet stringent; 3>, the valve stem is not connected securely to do with; 4>, stem bending and torsion , so that the upper and lower closure member misalignment; 5>, turn too fast, the sealing surface contact or already damaged; 6>, incorrect material selection, unable to withstand corrosive media; 7>, the cut-off valve, gate valve for regulating use, sealing surface withstand the impact of high speed of the flowing medium; 8>, some of the media, the valve is closed gradually cooled, so that the sealing surface appears slit, will produce erosion phenomenon; 9>, some seal with the valve seat, threaded connection between the use of the valve to do, easy to produce oxygen concentration cell, corrosion, loose; 10>, due to welding slag, rust, dust and other impurities embedded, or production system with mechanical blocking other pieces fall off the spool, so that the valve can not be Guan Yan.

C.Stem down failure

The reasons are: 1>, the operator makes excessive thread damage; 2>, the lack of lubricant or lubricant failure; 3>, stem bending and torsion; 4>, the surface finish is not enough; 5>, with tolerances allowed, bite tight; 6>, stem nut tilt; 7>, incorrect material selection; such as stem and stem nut for the same material, easy to bite; 8>, threaded wave medium corrosion (dark bar represents valves or valve stem in the lower valves); 9>, the lack of protection of open valve stem threads Nianman dust and sand, rust, etc. or is frost and rain.

D.Other

Body cracking : usually caused by freezing . When it's cold , the valve must be heating insulation measures, otherwise the valve should be halted and connecting pipe in the water drained ( if the valve end plugs , open the drain plugs ) . Handwheel damage : impact or long lever violently operation due. As long as the operator or other relevant personnel note , could have been avoided .

Gland rupture: compression packing when the force is uneven or gland is defective. Compression packing , to symmetrically rotating screw , can not skew . Manufacturing not only pay attention to large and critical pieces , but also pay attention to sub- elements of the gland and the like , or affect the use .

Stem gate connection failure : gate using stem rectangular head and ram connected to form large T-shaped slot , T-shaped groove sometimes not working , so to stem the rectangular head wear faster . Mainly from the manufacturing to solve. But the use of the T -line units can also fill slots for processing, so she has some finish.

Double plate gate valve is not pressure tight cover : double plate tension is generated by the top wedge , some valves , the top wedge material is poor ( low grade cast iron ) , the use of worn or broken soon . Top wedge is a small piece , replaced the original cast iron.

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