3
Capacities and Pressure Drop
CAPACITIESexpressed in CFH (m
3
/h)0.64 sp gr gas
Sizing Instructions
In order to select the proper size regulator, you must
know the available inlet pressure, desired outlet
pressure, and the required maximum flow rate.
Example No. 1To select a regulator of ample
capacity to handle flow.
KNOWN:
Pipe size 2-1/2", flow rate 8,000 CFH (0.64 sp gr), inlet
pressure 9" w.c., desired outlet pressure 5" w.c.
SOLUTION:
1. Determine differential pressure available:
Inlet pressure 9" w.c.
Subtract outlet pressure - 5" w.c.
Available differential pressure 4" w.c.
2. When determining capacity Maxitrol
recommends that the pressure drop not exceed
1/2 of available differential pressure (1/2 of 4"
w.c. = 2" w.c.).
3. Check Capacity Chart to determine which
regulator has a pressure drop of 2" w.c. or less at
a flow rate of 8,000 CFH.
4. The RV111 meets these standards with a
flow rate of 12,134 CFH for the 2-1/2" pipe size at
2" w.c. pressure drop. The 2-1/2" RV91 flows
5422 CFH at 2" w.c. pressure drop. Therefore, the
RV1112-1/2" is the correct regulator to use.
Example No. 2To determine maximum
recommended operating outlet pressure.
KNOWN:
Pipe size 4", flow rate 21,000 CFH, inlet pressure
10" w.c.
SOLUTION:
1. Check capacity Chart above for 4" regulator,
RV131.
2. Note that at a flow rate of 21,172 CFH the
pressure drop is 2" w.c.
3. Multiply this by two to obtain recommended
differential pressure (4" w.c.).
4. Subtract 4" differential pressure from 10" w.c.
inlet pressure to obtain maximum recommended
outlet pressure setting of 6" w.c.
Pressure Drop Chart
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