Applications Of The Check Valves
Check valve is a valve used to prevent medium backflow in pipes or equipment. It opens with the kinetic energy of the fluid. In the heating system, check valves are often installed at the outlet of the pump and other places where fluid flow is not allowed to reverse. The selection of suitable type of check valve has great influence on water hammer protection, for example, a large number of water hammer accidents in pump station are related to the check valve installed at pump outlet. After the accident stop pump flow through Beijing began to reverse flow, under the action of the reverse flow, the check valve quickly closed, if the check valve due to failure or support friction and its inertia effect, the check valve may lag behind the start of the reverse flow time, that is, in the reverse flow to a certain value, even in the moment of the maximum reverse flow quickly closed, can produce a very large pressure at the check valve. Check valve disc closed at zero flow is the best condition to close, it is not possible to complete disc closed at zero flow. It is generally assumed that it is normal to close near zero flow.
In the hot water heating system, in order to reduce the accident stop pump water hammer, the pressure relief bypass pipe with a check valve can be arranged between the pressure water pipe of the circulating pump and the suction pipe. When the circulating water pump is in operation, the check valve is closed because the water pressure on the outlet side of the pump is higher than that on the suction side. When the pump stops suddenly, the pressure of the pump outlet side decreases sharply, while the pressure of the suction side increases greatly. Under this pressure difference, the water in the suction side pipe of the circulating pump pushes the check valve to the pipe network system of the pump outlet side, thus reducing the increase of the pressure in the suction side pipe network; reducing and preventing the harm of the water hammer. The check valve of the device on the pressure relief bypass pipe should choose the product with less resistance and flexible opening.
The larger the pipe diameter of the pressure relief bypass pipe, the more powerful it is to reduce the water hammer, and the economic pipe diameter can be determined by transient calculation according to the prescribed pressure limit. There is no bypass pipe between the pressure pipe and the suction pipe of a heating system. When the circulating water pump is cut off, the calculation curve of the outlet pressure of the pump changes with time, and the calculation curve of the outlet pressure change of the pump after the pressure relief bypass pipe with check valve is added to the system. It can be seen from the diagram that increasing the bypass design with check valve is obviously effective for controlling the pressure of the water stop hammer; the pressure oscillation in the pipeline quickly attenuates to a new stable state. The amplitude of Zhuangtou fluctuation is also much smaller than when there is no bypass design.