Bulletin 71.1:95 AIR FLOW IN NORMAL CUBIC METERS PER HOUR
CE4967-A B0392-2
AIR FLOW IN THOUSANDS OF STANDARD CUBIC FEET PER HOUR
Figure 5. Air Flow Performance Curves of a 1-inch Type 95L Regulator
desired set point (see table 5 for part numbers of appropriate springs for each body size). See table 1 for sizing example for the Types 95HD and 95LD regulators. If closer control is necessary, a regulator of larger capacity or different design should be selected, so that the necessary flow can be obtained with a smaller offset factor. Sometimes it may be necessary to interpolate the capacity table data to determine capacity for outlet settings not given. To maintain accuracy, it is important when interpolating to stay within a spring range if possible. The following is a procedure for interpolating the data to calculate flow: 1. Determine which spring is to be used.
Example: P1 = 100 psig 1/4 inch Type 95H with 15 to 30 psig spring range P2 = 20 psig Determine air capacity, Q. Solution: Qa = 1000 SCFH P2a = 15 psig
Qb = 1900 SCFH P2b = 30 psig
1900 - 1000 30 - 15
=
1900 - Q 30 - 20
Q = 1300 SCFH
NOTE: The same interpolation procedure can be used for different inlet pressures.
2. Find the two outlet settings (P2a & P2b) that bracket the actual outlet pressure P2.
An alternative method for interpolating capacities is to back calculate Cv’s as shown in table 2.
3. For a given body size and inlet pressure, find the capacity Qa for P2a and Qb for P2b.
Contact your nearest Fisher Representative if you should have any questions about selecting the proper regulator.
4. Use the following formula to determine the interpolated capacity (Q). Qb - Qa P 2b - P 2a
=
Qb - Q P 2b - P 2
Air Capacities Regulating capacities at selected pressures and outlet pressure flows are given in SCFH (60_F and 14.7 psia) of air at 60_F. To determine the equivalent ca-
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