Restricted-Capacity Control Valve Trim

Most control valve manufacturers can provide valves with reduced- or restricted- capacity trim parts. The reduced flow rate might be desirable for any of the following reasons:

1.Restricted capacity trim may make it possible to select a valve body large enough for increased future flow requirements, but with trim capacity properly sized for present needs .

2.Valves can be selected for adequate structural strength, yet retain reasonable
travel/capacity relationship

3. Large bodies with restricted capacity trim can be used to reduce inlet and outlet fluid velocities.

4. Purchase of expensive pipeline reducers can be avoided

5. Over-sizing errors can be corrected by use of restricted capacity trim parts.

Conventional globe-style valve bodies can be fitted with seat rings with smaller port size than normal and valve plugs sized to fit those smaller ports.Valves with cage-guided trim often achieve the reduced capacity effect by utilizing valve plug, cage, and seat ring parts from a smaller valve size of similar construction and adapter pieces above the cage and below the seat ring to mate those smaller parts with the valve body (figure 1-28).Because reduced capacity service is not unusual,leading manufacturers provide readily available trim part combinations to perform the required function. Many restricted capacity trim combinations are designed to furnish approximately 40% of full-size trim capacity