Does the DN100 straight-through single-seat valve allow only a differential pressure of 120 kPa?
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Dear seniors, I have been reading a book titled \"Engineering Design and Application of Control Valves\" recently. In the section that discusses the classification of control valves, there is a statement regarding straight-through single-seat valves: \"It allows for a low differential pressure; for example, a valve with DN100 size only permits a differential pressure of 120 kPa.\" There is also a mention that straight-through double-seat valves with DN100 size can tolerate a differential pressure of 280 kPa. I’m a bit confused – isn’t the allowable differential pressure of a control valve related to the maximum thrust of its actuator? Does that mean that even if I use an actuator with high thrust for a DN100 straight-through single-seat valve, its allowable differential pressure will still be only 120 kPa?
This statement is incorrect; it depends on the magnitude of the actuator force.
It is also considered a bit small; furthermore, when it comes to the maximum pressure difference, attention must be paid to the issue of critical flow. In simple terms, this refers to noise – when the pressure difference is too high, the noise level becomes very high, and vibrations may occur as well, posing safety risks.
At what pressure difference should one start to consider noise and vibration issues?
Typically, the regulating pressure difference for control valves is set at 50 kPa (0.5 bar), which is related to the calculation of the flow coefficient Kv. If a regulation pressure difference of 120 kPa is required, a smaller Kv value should be selected. The thrust selection of the actuator is related to the closing pressure difference of the control valve (the pressure before the valve is the absolute pressure of the maximum operating pressure, while the pressure after the valve is absolute pressure 1).
Generally, critical flow occurs when the pressure difference is about half of the inlet pressure.