# Pressure Loss Due to Fluid Flow Through Pipes

## FLUID POWER - Design Data Sheet 57

This table has been calculated from a formula published by the Crane Co. on pages 3-12 of Technical Paper 410. It shows the approximate pressure loss per 100 feet of Schedule 40 pipe with hydraulic oil of known specific gravity and known viscosity flowing through it.

The formula used is: ΔP = 0.0668 μv ÷ D², in which: ΔP is pressure loss per 100 feet of pipe;

μ is viscosity in centipoises (not SSU);
v is flow velocity in feet per second;
D is inside diameter of pipe, in inches.

Note: Absolute viscosity in centipoises must be used in the formula. For any fluid this is the kinematic viscosity in centistokes times the specific gravity. An absolute viscosity of 40 centipoises was used for calculating the table. This corresponds approximately to a hydraulic oil with 0.9 specific gravity and a viscosity of 220 SSU (or 44.4 centicentipoises stokes). See back side of sheet for other fluids.

Table 1. Pressure loss per 100 feet schedule 40 pipe with oil of 220 SSU and 0.9 specific gravity

 GPM Pipe Size* Pres. Drop** Flow Veloc† GPM Pipe Size* Pres. Drop** Flow Veloc† GPM Pipe Size* Pres. Drop** Flow Veloc† 3 1/8 624 17 35 1/2 249 36 90 1 80 33 1/4 187 9.3 3/4 83 21 1¼ 27 19 3/8 55 5.0 1 32 13 1½ 15 14 1/2 22 3.2 1¼ 11 7.5 2 5.4 8.6 3/4 7.1 1.8 1½ 5.7 5.5 2½ 2.6 6.0 6 1/4 373 19 40 3/4 95 24 100 1 92 38 3/8 111 10 1 36 15 1¼ 30 22 1/2 44 6.3 1¼ 12 8.6 1½ 16 16 3/4 14 3.6 1½ 6.5 6.3 2 6.0 9.6 1 5.4 2.2 2 2.4 3.8 2½ 2.9 6.7 10 3/8 185 17 45 3/4 106 27 125 1 114 47 1/2 73 11 1 41 17 1¼ 38 27 3/4 24 6.0 1¼ 14 9.7 1½ 20 20 1 9.0 3.7 1½ 4.4 7.1 2 7.5 12 1¼ 3.0 2.2 2 2.7 4.3 2½ 9.8 8.4 15 1/2 109 16 50 3/4 122 31 150 1¼ 44 31 3/4 36 9.0 1 46 19 1½ 24 24 1 14 5.6 1¼ 15 11 2 8.9 14 1¼ 4.5 3.2 1½ 8.1 7.9 2½ 4.4 10 1½ 2.4 2.4 2 3.0 4.8 3 1.8 6.4 20 1/2 146 21 60 3/4 142 36 175 1¼ 53 38 3/4 47 12 1 53 22 1½ 29 28 1 18 7.4 1¼ 18 13 2 10 17 1¼ 6.0 4.3 1½ 9.8 9.5 2½ 5.1 12 1½ 3.2 3.2 2 3.6 5.7 3 2.2 7.6 25 1/2 180 26 70 3/4 205 42 200 1¼ 60 43 3/4 59 15 1 63 26 1½ 32 31 1 23 9.3 1¼ 21 15 2 12 19 1¼ 7.6 5.4 1½ 11 11 2½ 5.9 13 1½ 4.0 3.9 2 4.2 6.7 3 2.5 8.7 30 1/2 214 31 80 1 75 31 225 1¼ 69 49 3/4 71 18 1¼ 24 17 1½ 37 36 1 27 11 1½ 13 13 2 13 22 1¼ 9.0 6.4 2 4.8 7.7 2½ 6.6 15 1½ 4.8 4.7 2½ 2.3 5.4 3 2.8 9.8 *Standard Schedule 40 pipe **Pressure loss per 100 feet of pipe †Oil flow velocity in feet per second

For pressure loss per 100 feet of steel tubing, use the nearest NPT size shown in this table. Find pressure loss from Table 1 on front side of this sheet. Then multiply this loss times the factor shown in the last column of this table.

Example: For a flow of 50 GPM through a tube of 1½˝ O.D. with 0.095 wall, use the 1¼˝ pipe size under 50 GPM in Table 1. This shows a 15 PSI loss per 100 feet. Multiply this times 0.981 from Table 2 = 14.71 PSI per 100 feet loss.

Table 2. Conversion factors for using Table 1 for steel tubing

 Tube O.D. Wall Thick. Tube I.D. Use NPT Mult. By Tube O.D. Wall Thick. Tube I.D. Use NPT Mult. By Tube O.D. Wall Thick. Tube I.D. Use NPT Mult. By 3/16 0.032 0.124 1/4 8.69 3/4 0.049 0.652 1/2 0.910 1¼ 0.072 1.106 1 0.901 1/4 0.035 0.180 1/4 4.09 0.058 0.634 1/2 0.962 0.083 1.084 1 0.938 0.042 0.166 1/4 4.81 0.065 0.620 1/2 1.01 0.095 1.060 1 0.981 0.049 0.152 1/4 5.73 0.072 0.606 1/2 1.08 0.109 1.032 1 1.03 0.058 0.134 1/4 7.38 0.083 0.584 1/2 1.13 0.120 1.010 1 1.08 0.065 0.120 1/4 9.20 0.095 0.560 1/2 1.23 1½ 0.065 1.370 1¼ 1.01 3/8 0.035 0.305 1/4 1.42 0.109 0.532 1/2 1.37 0.072 1.356 1¼ 1.04 0.042 0.291 1/4 1.56 1 0.049 0.902 3/4 0.835 0.083 1.334 1¼ 1.07 0.049 0.277 1/4 1.73 0.058 0.884 3/4 0.869 0.095 1.310 1¼ 1.11 0.058 0.259 1/4 1.97 0.065 0.870 3/4 0.897 0.109 1.282 1¼ 1.16 0.065 0.245 1/4 2.21 0.072 0.856 3/4 0.927 0.120 1.260 1¼ 1.20 1/2 0.035 0.430 3/8 1.31 0.083 0.834 3/4 0.976 2 0.065 1.870 2 1.22 0.042 0.416 3/8 1.40 0.095 0.810 3/4 1.03 0.072 1.856 2 1.24 0.049 0.402 3/8 1.50 0.109 0.782 3/4 1.11 0.083 1.834 2 1.27 0.058 0.384 3/8 1.65 0.120 0.760 3/4 1.18 0.095 1.810 2 1.30 0.065 0.370 3/8 1.78 1¼ 0.049 1.152 1 0.830 0.109 1.782 2 1.35 0.072 0.356 3/8 2.01 0.058 1.134 1 0.857 0.120 1.760 2 1.38 0.083 0.334 3/8 2.18 0.065 1.120 1 0.878 0.134 1.732 2 1.42

How to Adjust for Other Fluids and Conditions
To use the information on this data sheet, first find the multiplying factor, if necessary, to convert from Schedule 40 to other schedules or to steel tubing. Follow instructions above Table 2 to find the multiplying factor.

Next, use Table 1 regardless of the kind of fluid used, to find the pressure loss per 100 feet. If applicable, use conversion factor obtained from Table 2. Use Table 3 to adjust for viscosities other than 220 SSU. If using a fluid other than oil, adjust for its gravity as explained in opposite column.

Generally, as shown by the formula on the front side of this sheet, pressure loss increases in direct proportion to an increase in velocity. This can be seen also in Table 1.

Always keep in mind that centistoke viscosity defines only the flow resistance to shear in the fluid. Centipoise viscosity defines the combined flow resistance including both shear in the fluid and specific gravity. Centipoises = Centistokes × specific gravity.

Pressure loss through a pipe is directly proportional to viscosity in centistokes (for a given specific gravity). This table may be used with the chart on the front side to adjust pressure loss per 100 feet to oil with viscosity other than 220 SSU.

Example: A hydraulic oil of 500 SSU will have a higher pressure loss than shown in the table by a factor of 2.48 for the same size pipe and the same flow. In using Table 3, multiply factor in 3rd column times the pressure loss shown in Table 1.

Water is a special case. For straight water, pressure loss will be approximately half the values shown in Table 1.

Table 3.

 SSU Vis. Centistokes Factor 80 15.8 0.356 100 20.8 0.468 150 33 0.743 300 65 1.46 400 87 1.96 500 110 2.48 750 163 3.67 1,000 220 4.95 2,000 420 9.46 3,000 630 14.2 4,000 850 19.1

Pressure loss through a pipe is directly proportional to specific gravity of the fluid. Other hydraulic fluids have a higher specific gravity than petroleum oil and (at the same viscosity) will have a higher pressure loss. Water/oil emulsions will have 7% higher, water/glycol will have 14% higher, and phosphate ester will have 22% higher pressure loss than petroleum hydraulic oil.

Table 4. Pressure Loss Through Fittings
Pressure loss through common fittings is shown in terms of the equivalent length of straight pipe of the same size.

Example: The flow from the side outlet of a 1½" tee suffers the same pressure loss as if it were flowing through a 9 foot straight length of the same pipe. For pipe sizes less than 1/2", pressure loss through fittings is little more than for a straight section of the same length. (The Crane Company).

Table 4. Pressure loss through fittings

 NPT Pipe Size 1/2˝ 3/4˝ 1˝ 1¼˝ 1½˝ 2˝ 2½˝ 3˝ 3½˝ Tee, Side 3½ 4½ 5½ 7½ 9 11½ 14 16½ 20 45° Elbow ¾ 1 1¼ 1¾ 2 2½ 3 3¾ 4½ 90° Elbow 1½ 2 2¾ 3¼ 4¼ 5 6 8 9½

© 1990 by Womack Machine Supply Co. This company assumes no liability for errors in data nor in safe and/or satisfactory operation of equipment designed from this information.