Pressure drop ratings are typically a function of the valve type, trim style, materials of construction, and fluid temperature. Manufacturers may publish maximum pressure drop ratings for a complete valve assembly, or they may publish ratings for individual trim components.
Pressure Drop Charts – Figure 10 includes a chart that shows, in relation to temperature limits, the maximum pressure drop ratings of various trim options for a typical Fisher control valve. The numbers designate specific trim material options. The materials that are used in each option are listed in a corresponding table. For a complete list of standard trim options for a typical control valve, refer to Figure 7 and Table 2 of Fisher Specification Bulletin 51.1:ED (Fisher Catalog 71).
Selection Guidelines – The lowest available trim number designates a standard trim. Trim options with higher numbers may provide increased pressure drop or temperature ratings, corrosion resistance to certain fluids, and/or increased erosion resistance. Generally speaking, the lowest trim number that satisfies all requirements is the trim option that should be selected. Note that the charts provide selection guidance with respect to pressure drop and temperature limits only.
Pressure Drop Tables – Pressure drop ratings may also be published in tabular form. The pressure drop table that is shown in Figure 11 lists the pressure drop ratings for a Fisher V-200 rotary-shaft control valve. Note that the pressure drop rating depends on the materials of construction, the seal type, the operating temperature, and the valve size.
