COMMON VALVE TYPES
Needle Valves
The families that appear on first RFQs and Chinese export quotes. Shared names are not interchangeable designs.
Choosing Needle Valves
A needle valve uses a fine stem-tip movement to restrict a relatively small passage. It is useful when a buyer needs controlled adjustment or instrument isolation, but flow capacity depends on the orifice and stem design. Connection size should not be used as a proxy for the available flow.
What to include in the RFQ
- Provide required flow, inlet and outlet pressures, and acceptable pressure loss.
- Request the stem-tip construction, flow coefficient and adjustment resolution.
- Specify seat and stem-seal materials, temperature and the actual fluid.
- Identify the complete end-connection standard and required isolation or metering function.
A published design example
The Swagelok D-series catalogue separates orifice sizes and flow coefficients within one needle-valve family; equal connection sizes need not imply equal capacity.
Selection scenario
In an instrument branch, specify whether the valve must isolate, meter a sample, or both. Compare the published capacity and stem arrangement with the required range, especially when two candidates have the same tube connection.
Common selection mismatch
A fine-adjustment stem does not establish a universal shut-off leakage class. Request separate metering and seat-tightness evidence.