Before the valve is out of plant, it has to undergo many tests. The sealing performance test is one of them, and the sealing performance is one of the important indices to check whether
the valve is qualified or not. So, how many
seal forms of the valve are there?
No matter
pneumatic ball valves or
electric ones, their sealing positions are the same and there are three positions: the contact point between the disc and valve seat, the position between packing and the stem and stuffing box, and the joint between the valve body and the bonnet. If the first part leaks, it belongs to internal leakage, which will affect the shutoff ability of the valve. The latter two leaks are external leakage, causing the medium to flow out of the valve and resulting in raw material losses and pollution. Therefore, valve leakage must be avoided.
Generally,
seal forms of valves can be classified into two classes: dynamic sealing and static sealing. The former mainly refers to the valve stem seal, which prevents leakage of the medium caused by movement of the valve stem. The valve stem seal can be subdivided into the packing box seal, the packing seal and the bellows seal. The latter refers to sealing between two static surfaces, and sealing is achieved by the gasket. Commonly used gasket materials include nonmetal (asbestos), metal (stainless steel) and composite materials (soft sealing butterfly valves), etc.
Generally, the manufacturer will choose the seal form and sealing materials as required. After all, the nature of the medium and the use environment will directly affect the material selection, and then the product will be tested after the production to ensure good sealing performance.
