1. Determine required turnover rate for spa in gallons per minute (GPM).
2. Determine GPM and PSI needed for maximum jet performance (use Jet Performance Flow Curves).
3. A. Figure resistance head of system:
From Friction Flow Chart and Friction Loss in Fittings, convert fittings and pipe lengths into feet of head.
EXAMPLE:
A. (4) 2" 90° elbows = 4 x 8.6 = 34.4 feet of 2" pipe
B. 50 feet of 2" pipe = 50 feet
A + B: 34.4 feet + 50 feet = 84.4 feet
Looking at the Friction Flow Chart, 2" pipe at 10 feet per second gives us 100 GPM at 14.4 feet of head. This is figured in 100 foot length of pipe. We multiply .844 times 14.4 = 12.15 feet of head. Or to convert to PSI x .433 = 5.26 PSI loss.
B. Figure Actual Head Loss of Components: (Refer to Head Loss Chart)
EXAMPLE:
1) One 1 1/2" main drain at 50 GPM has 2 feet of head.
2) One 1 1/2" skimmer 50 GPM has 4 feet of head.
Total head loss of components is 6 feet of head.
C. Add Head Loss from B and C for Total Resistance Head:
EXAMPLE:
12.15 feet of head (from system resistance) + 6 feet of head (from component head loss) = 18.15 feet of head
D. Total of B and C is TDH (total dynamic head) of system. Convert total head into PSI by multiplying by .433:
EXAMPLE:
18.15 feet of head x .433 = 7.86 PSI
(This is the amount of pressure lost in the system)
E. Add Target PSI from Jet Worksheet (or Line #2) to Total Pressure Loss (PSI) Line D to find Total Pressure Required and Total Dynamic Head of System:
EXAMPLE:
14 PSI (Required for jets) + 7.86 PSI (Required for system) = 21.86
F. Match appropriate pump by looking at pump curves.
EXAMPLE:
At 22 PSI (or 50 feet of head) at 100 GPM, you can use The Executive 1 HP Pump or a 2 HP Hi-Flo Side Discharge Pump