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A 104.0 Permissible Friction Loss
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Decide what is the desirable minimum residual pressure that shall be maintained at the highest fixture in the supply system. Where the highest group of fixtures contains flushometer valves, the residual pressure for the group shall be not less than 15 pounds-force per square inch (psi) (103 kPa). For flush tank supplies, the available residual pressure shall be not less than 8 psi (55 kPa).
Determine the elevation of the highest fixture or group of fixtures above the water (street) main. Multiply this difference in elevation by 0.43. The result is the loss of static pressure in psi (kPa).
Subtract the sum of loss in static pressure and the residual pressure to be maintained at the highest fixture from the average minimum daily service pressure. The result will be the pressure available for friction loss in the supply pipes, where no water meter is used. Where a meter is to be installed, the friction loss in the meter for the estimated maximum demand should also be subtracted from the service pressure to determine the pressure loss available for friction loss in the supply pipes.
Determine the developed length of pipe from the water (street) main to the highest fixture. Where close estimates are desired, compute with the aid of Table A 104.4(1), Table A 104.4(2), or Table A 104.4(3), whichever is applicable, the equivalent length of pipe for fittings in the line from the water (street) main to the highest fixture and add the sum to the developed length. The pressure available for friction loss in psi (kPa), divided by the developed lengths of pipe from the water (street) main to the highest fixture, times 100, will be the average permissible friction loss per 100 feet (30 480 mm) length of pipe.
TABLE A 104.4(1)
ALLOWANCE IN EQUIVALENT LENGTH OF PIPE FOR FRICTION LOSS IN VALVES AND THREADED FITTINGS*
EQUIVALENT LENGTH OF PIPE FOR VARIOUS FITTINGS
ALLOWANCE IN EQUIVALENT LENGTH OF PIPE FOR FRICTION LOSS IN VALVES AND THREADED FITTINGS*
EQUIVALENT LENGTH OF PIPE FOR VARIOUS FITTINGS
| DIAMETER OF FITTING (inches) | 90° STANDARD ELBOW (feet) | 45° STANDARD ELBOW (feet) | 90° STANDARD TEE (feet) | COUPLING OR STRAIGHT RUN OF TEE (feet) | GATE VALVE (feet) | GLOBE VALVE (feet) | ANGLE VALVE (feet) |
|---|---|---|---|---|---|---|---|
| 3/8 | 1.0 | 0.6 | 1.5 | 0.3 | 0.2 | 8 | 4 |
| 1/2 | 2.0 | 1.2 | 3.0 | 0.6 | 0.4 | 15 | 8 |
| 3/4 | 2.5 | 1.5 | 4.0 | 0.8 | 0.5 | 20 | 12 |
| 1 | 3.0 | 1.8 | 5.0 | 0.9 | 0.6 | 25 | 15 |
| 11/4 | 4.0 | 2.4 | 6.0 | 1.2 | 0.8 | 35 | 18 |
| 11/2 | 5.0 | 3.0 | 7.0 | 1.5 | 1.0 | 45 | 22 |
| 2 | 7.0 | 4.0 | 10.0 | 2.0 | 1.3 | 55 | 28 |
| 21/2 | 8.0 | 5.0 | 12.0 | 2.5 | 1.6 | 65 | 34 |
| 3 | 10.0 | 6.0 | 15.0 | 3.0 | 2.0 | 80 | 40 |
| 4 | 14.0 | 8.0 | 21.0 | 4.0 | 2.7 | 125 | 55 |
| 5 | 17.0 | 10.0 | 25.0 | 5.0 | 3.3 | 140 | 70 |
| 6 | 20.0 | 12.0 | 30.0 | 6.0 | 4.0 | 165 | 80 |
For SI units: 1 inch = 25 mm, 1 foot = 304.8 mm, 1 degree = 0.017 rad
* Allowances are based on nonrecessed threaded fittings. Use one-half the allowances for recessed threaded fittings or streamlined solder fittings.
| DIAMETER OF FITTING (inches) | 90 DEGREE ELBOW (feet) | 45 DEGREE ELBOW (feet) | COUPLING OR STRAIGHT RUN OF TEE (feet) | 90 DEGREE STANDARD TEE (feet) |
|---|---|---|---|---|
| 1/2 | 1.6 | 0.8 | 1.0 | 3.1 |
| 3/4 | 2.1 | 1.1 | 1.4 | 4.1 |
| 1 | 2.6 | 1.4 | 1.7 | 5.3 |
| 11/4 | 3.5 | 1.8 | 2.3 | 6.9 |
| 11/2 | 4.0 | 2.1 | 2.7 | 8.1 |
| 2 | 5.2 | 2.8 | 3.5 | 10.3 |
For SI units: 1 inch = 25 mm, 1 foot = 304.8 mm
| DIAMETER OF FITTING (inches) | 90 DEGREE ELBOW (feet) | 45 DEGREE ELBOW (feet) | COUPLING OR STRAIGHT RUN OF TEE (feet) | 90 DEGREE STANDARD TEE (feet) |
|---|---|---|---|---|
| 1/2 | 1.5 | 0.8 | 1.0 | 4.0 |
| 3/4 | 2.0 | 1.1 | 1.4 | 5.0 |
| 1 | 2.5 | 1.4 | 1.7 | 6.0 |
| 11/4 | 3.8 | 1.8 | 2.3 | 7.0 |
| 11/2 | 4.0 | 2.1 | 2.7 | 8.0 |
| 2 | 5.7 | 2.6 | 4.3 | 12.0 |
For SI units: 1 inch = 25 mm, 1 foot = 304.8 mm
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