Calculation of Auto Bypass Valve

Procedure for calculating and selecting an auto bypass valve

The auto bypass valve opens when the pressure drop between the inlet and outlet connections exceeds the set pressure. The calculation of the auto bypass valve involves determining the range of set pressure and flow capacity.

An auto bypass valve cannot maintain a constant pressure between the inlet and outlet connections when the flow rate through it changes. This means that a valve with an opening pressure of 0.2 bar will open when the pressure drop between the inlet and outlet connections is 0.2 bar, and when the pressure and flow rate subsequently increase, the valve will open more, but the pressure at its connection point will already exceed the set value. The degree of pressure deviation when the flow rate increases can be determined from the graphs presented in the technical description of the auto bypass valves.

If precise pressure control is required at the place where the auto bypass valve is installed as part of the technological process, a pressure drop regulator that opens when the set pressure increases should be used.

The selection of the size and type is made using the diagrams presented in the technical specifications of the auto bypass valves or based on their flow capacity. The above algorithm selects an auto bypass valve based on its flow capacity, but since the manufacturers of some models do not specify their flow capacity, its value was obtained by calculation. In any case, the selected size and type of auto bypass valve should be checked for compliance with the initial data using the diagram, paying attention to the opening pressure and the pressure corresponding to the calculated flow rate.

When selecting the pressure range of an auto bypass valve, there is no need to choose a range in which the maintained pressure will be in the middle third, as would be done when selecting a pressure regulator. Auto bypass valves maintain the available pressure with the same accuracy regardless of how close the set pressure is to the edge of the regulated range.

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