Why pneumatic valve strength test before installation?

to install in the ceiling and pneumatic valve is required to cut off the medium flow in a tube well more strict pneumatic valve of water supply system, large diameter valve pneumatic conveying inflammable and explosive medium of the pneumatic valve in the pipeline, etc. , are dealing with pneumatic valve and monomer strength test. At present, the domestic production of pneumatic valve manufacturers, product quality is uneven, often open shut down several times after water namely appear all sorts of quality problems. When there is a sealing surface scratches or closed lax, can adopt the method of manual grinding or mechanical polishing, restore its sealing performance.
manual grinding can refer to the following method:
( ） First of all to prepare a clean workbench and strength test equipment ( Hydraulic test pump inflow, pipes, etc. ) , the pressure gauge should be used after checking.
　　（ ） Removing the pneumatic valve stem and packing gland, exposed the sealing surface. Defects such as scratches depth is greater than. Mm, can be grinding on the precision lathe finishing once again. As to the naked eye can't identify the presence of notch, zhang thin lead powder coating is available on the seal, then gently with calibration plate rotation, zhang reserved lead powder inside notch, make can be found that the number of indentation and position.
　　（ ） Then the grinding surface and abrasive with kerosene to wipe clean, coated with a thin layer on the surface of the need to grinding paste ( Jules verne sand) On the grinding, grinding tool for reciprocating rotation, washed with kerosene, replace the abrasive continue to grind, until qualified.
　　（ ） The sealing surface with a soft cloth rub-up, pneumatic valve will be assembled, the packing reject change of packing.
　　（ ） After grinding of pneumatic valve, and then to strength test, qualified after the installation.