Useful
Plumbing Design Formulas, Tables & Tips.
Domestic Water
| 2.31 feet of head = 1 psi |
1 foot of head = .433 psi |
28" of water column = 1 psi |
| 1 gallon weighs 8.33 pounds |
7.5 gallons occupy 1 cubic foot |
1 gallon occupies 231 cubic inches |
| TYPE |
HARDNESS (parts
per million) |
HARDNESS (grains
per gallon) |
| Soft |
0 - 49 |
0 - 3 |
| Fairly Soft |
50 - 99 |
3 - 6 |
| Fairly Hard |
100 -149 |
6 -9 |
| Hard |
150 -249 |
9 -14.5 |
| Very Hard |
250 plus |
14.5 plus |
Domestic Hot Water
- 1 BTU will raise 1 pound of water 1° F.
- 1 BTU will raise .12 gallons of water 1° F.
- 1 KW = 3413 BTU° F.
Water Heating Calculations
- Natural Gas
- BTU/Input = GPH x 8.25 x Temp.Rise x 1.0 -
divided by - %Efficiency of heater
- Gal/Per/Hour = Btu/Hr Input x %Efficiency
- divided by - Temp.Rise x 8.25
- Electric
- KW = GPH x 8.25 x Temp.Rise x 1.0 -
divided by - 3413 Or… GPH x Temp.Rise - divided by -
414
- Gal/Per/Hour = KW x %3413 - divided by -
Temp.Rise x 8.25 Or… KW x 414 - divided by - Temp.Rise
BTU CONTENT of VARIOUS
FUELS
| Fuel |
Amount |
BTU |
| Coal |
1pound |
10,000 - 15,000 |
| Coal |
1 ton |
25,000,000 |
| Electricity |
1 kilowatt |
3,412 |
| #2 Oil |
1 gallon |
138,500 |
| Butane |
1 pound |
21,300 |
| Butane |
1 gallon |
102,600 |
| Butane |
1 cubic foot |
3,260 |
| Natural Gas |
1 cubic foot |
1,000 |
| Propane |
1 pound |
21,600 |
| Propane |
1 gallon |
91,000 |
| Propane |
1 cubic foot |
2,570 |
Natural Gas
- 1 psi = 28" water column.
- 1 psi = 16 ounces.
- 1psi = 2.036 inches of mercury
Storm Drainage
- 1 inch rainfall rate = .0104 gallons per
minute per square foot.
- 1 cubic foot per second = 448.831 gallons
per minute.
- Formula (rational method) to Determine
Storm Runoff on a Site Q = CIA
Q = Runoff in cubic feet per second
C = Coefficient of runoff I = Intensity of rainfall in inches per hour
A = Drainage area in acres (43,560 square
feet per acre)
| |
RUNOFF COEFFICIENTS |
|
| Type of Surface |
Description |
Coefficient of Runoff |
| Grass |
Rough grass or undeveloped land
|
.10 |
| Grass |
Average developed lawn |
.20 |
| Grass |
Sparse lawn on hard ground |
.25 |
| Paved |
Rough surface on flat slopes
|
.80 |
| Paved |
Average pavement |
.85 |
| Roof |
Flat roof with provisions for
standing water |
.85 |
| Roof |
All other roof surfaces |
.95 |
| Composite |
Average value for entire site area
|
.55 - .75 |
(Note: Composite value depends upon
relative amount of lawn area)
Miscellaneous
Volume of Liquid in a Tank
- Gallons = 5.875 x Diameter squared x
Height {dimensions must be in feet}
- Gallons = (Radius squared x 3.14) x Length
divided by 231 {dimensions must be in inches}
Tips
- Remember to provide a properly sized
expansion tank in the cold water supply to a hot water
heater when a check valve or backflow preventer is
installed in the water service.
- The jockey pump capacity for a fire pump
should be 2 to 3 percent of the fire pump capacity and be
set to start at 10 psi above the start pressure setting
of the fire pump.
- Natural gas is lighter than air. Propane
and Butane are heavier than air. Propane and Butane
normally are supplied in cylinders at a pressure of 80 to
120 psi. LPG cylinders should not be located in vaults or
pits unless they are mechanically ventilated. When LPG
cylinders are located in a room, vents must be located at
floor level.
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