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A swing check valve is a flow control instrument that contains some type of closing panel that rotates one way on a hinge. The valve itself can be connected to various other chambers and pipes to prevent liquids or solids from entering another area of the unit, and this is accomplished by the actual weight of the material applying pressure and sealing the barrier in place or forcing it open. Normally, a swing check valve is activated from a manual or mechanical source that allows the barrier to lift and expel the contents, but they also can be designed to expel all materials from within a chamber and prevent them from re-entering as well.
One of the most common applications of a check swing valve can be observed by removing the lid from a toilet and inspecting the mechanism that prevents water from entering the lower tank. By design, the combined weight of the liquid inside the toilet prevents the flapper from allowing any water to escape, yet when minor amounts of pressure are applied to the flush lever, it raises the rubber stopper enough for the flushing process to occur. The check swing valve then remains open until the area is almost completely devoid of liquid, and after the pressure is fully released, the valve falls back into place for the process to begin again. Another practical example of this technology would be the release mechanism inside a fire extinguisher.
Another type of swing check valve functions with the aid of springs to allow for the unrestricted flow of liquids of solids, such as the type found inside a grain silo. When processed elements are dumped into the main chamber, a large swing check valve does not attempt to regulate the amount of product entering the lower area; as long as the movement of grain is constant, the valve remains open and does not attempt to close. After the influx of materials slows dramatically or ceases, the spring mechanism has enough strength to activate and seal off the valve chamber to prevent the stored grains from escaping.
Other types of swing check valves are used in various configurations to equalize the pressure on both sides of a mechanism and to prevent a buildup of internal gases or other strains on the equipment. A smaller swing check valve that is not required to withstand large amounts of pressure is normally constructed from plastic or rubber. The ones that face more demanding heavy-duty uses are constructed from steel or various other metals.