COMMON VALVE TYPES
Control Valves
The families that appear on first RFQs and Chinese export quotes. Shared names are not interchangeable designs.
Choosing Control Valves
A control valve is selected as part of a regulating loop. The body, trim, actuator and accessories must work over the required operating range. Pipe diameter and a maximum flow figure do not establish the needed capacity, stability or shut-off behavior.
What to include in the RFQ
- Provide minimum, normal and maximum flow with corresponding inlet and outlet pressures and temperatures.
- Request the sizing calculation, selected flow coefficient, characteristic and predicted opening at each condition.
- Include cavitation, flashing, noise and material checks where the service requires them.
- Specify shut-off acceptance, fail position, positioner signal, feedback and available actuator supply.
Selection scenario
For a variable-load process, compare predicted opening at both low and high demand. A valve sized only for the maximum case may operate in an unsuitable part of its travel during most of the operating hours.
Common selection mismatch
Do not equate body size with trim capacity or a positioner with adequate sizing. The bidder should identify the complete assembly and calculation basis.