Hydraulic Oil Flow through Orifices

The chart shows approximate pressure drops which may be expected at various flows rates through sharp edge orifices for petroleum type hydraulic oil. It may be used for designing limiting flow orifices in hydraulic systems. Chart values must be considered as approximate because a number of factors such as specific gravity, orifice efficiency, plumbing ahead of and behind the orifice may cause variations from the values shown.

By making the orifice with a knife edge, it becomes insensitive to temperature, and the flow and pressure drop will remain the same over a reasonable range of oil temperatures (and viscosity changes).

Specific gravity of the fluid makes a significant difference in the pressure drop through a given orifice, and increases approximately as the square of the increase in specific gravity, The chart was calculated for a fluid with 0.9 specific gravity, a close approximation for all petroleum hydraulic oils. Using a heavier fluid, a multiplying factor should be applied to chart values. For example, to find the pressure drop of water, with a specific gravity of 1.00:

(1.00)2 ÷ (0.9)2 = 1.00 ÷ 0.81 = 1.23 multiplying factor.

Multiply all chart values by 1.23 for water flow.

The chart was calculated from information furnished by Double A Products Co., in which the constant 23.5 was developed by trial and error for average orifices. For values not shown in the chart, use this formula:

Pressure Drop (ΔP) = [GPM ÷ (23.5 × A)]2

in which, A = Orifice Area, Sq. ln.

Figures in this chart are PSI pressure drops across sharp edge orifices, petroleum type hydraulic oil.

 Orifice Diameter, Inches GPM 3/64 1/16 5/64 3/32 7/64 1/8 9/64 5/32 11/64 3/16 13/64 7/32 15/64 1/4 5/16 3/8 7/16 1/2 3 5440 1730 710 333 184 108 68 44 30 21 16 12 9 7 3 1 - - - - - - 5 - - - 4800 1970 925 512 300 188 123 84 59 43 32 24 19 8 4 2 1 10 - - - - - - - - - 3700 2050 1200 750 490 336 238 172 128 97 75 31 15 8 5 15 - - - - - - - - - - - - 4600 2700 1690 1100 757 534 388 288 219 169 69 33 18 11 20 - - - - - - - - - - - - - - - 4800 3000 1968 1345 950 690 513 390 300 123 59 32 19 30 - - - - - - - - - - - - - - - - - - 6750 4430 3025 2135 1550 1155 875 675 275 135 72 42 40 - - - - - - - - - - - - - - - - - - - - - - - - 5380 3800 2760 2050 1555 1205 495 235 128 75 50 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4310 3205 2430 1880 770 370 200 118 60 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4615 3500 2705 1110 535 288 170 70 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4765 3685 1510 725 390 230 80 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4810 1970 950 510 300 100 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3080 1480 800 470

Chart Figures are PSI

Caution! Calculated values of pressure drop are approximate. Drill orifice undersize to start and run a preliminary test; then enlarge as necessary using standard twist drills. Countersink finished hole for a sharp edge.

 Figure 1. Pipe Union Orifice. For low pressure applications using steel pipe, a very thin orifice plate may be installed in a gasket-type union as indicated in this figure. Figure 2. High Pressure Systems. An orifice plug may be installed next to a nipple, elbow, or tee. A shoulder on the plug keeps it from being pushed out of place by hydraulic pressure. Be sure plug is installed with shoulder facing toward the pressure. The orifice plug must be machined by the user. It should be a press fit in the fitting. Remember, the sharper the edge of the orifice, the less the flow and pressure drop will be affected by changes in the fluid viscosity and temperature.

COMPRESSED AIR FLOW THROUGH ORIFICES

Figures in the chart are theoretical SCFM air flows through perfect orifices (See text)

 PSI Across Orifice Orifice Diameter in Inches 1/64 1/32 1/16 1/8 1/4 3/8 1/2 5/8 3/4 7/8 1 5 0.062 0.248 0.993 3.97 15.9 35.7 63.5 99.3 143 195 254 6 0.068 0.272 1.09 4.34 17.4 39.1 69.5 109 156 213 278 7 0.073 0.293 1.17 4.68 18.7 42.2 75.0 117 168 230 300 9 0.083 0.331 1.32 5.30 21.2 47.7 84.7 132 191 260 339 12 0.095 0.379 1.52 6.07 24.3 54.6 97.0 152 218 297 388 15 0.105 0.420 1.68 6.72 26.9 60.5 108 168 242 32 430 20 0.123 0.491 1.96 7.86 31.4 70.7 126 196 283 385 503 25 0.140 0.562 2.25 8.98 35.9 8039 144 225 323 440 575 30 0.158 0.633 2.53 10.1 40.5 91.1 162 253 365 496 648 35 0.176 0.703 2.81 11.3 45.0 101 180 281 405 551 720 40 0.194 0.774 3.10 12.4 49.6 112 198 310 446 607 793 45 0.211 0.845 3.38 13.5 54.1 122 216 338 487 662 865 50 0.229 0.916 3.66 14.7 58.6 132 235 366 528 718 938 60 0.264 1.03 4.23 16.9 67.6 152 271 423 609 828 1082 70 0.300 1.20 4.79 19.2 76.7 173 307 479 690 939 1227 80 0.355 1.34 5.36 21.4 85.7 193 343 536 771 1050 1371 90 0.370 1.48 5.92 23.7 94.8 213 379 592 853 1161 1516 100 0.406 1.62 6.49 26.0 104 234 415 649 934 1272 1661 110 0.441 1.76 7.05 28.2 113 254 452 705 1016 1383 1806 120 0.476 1.91 7.62 30.5 122 274 488 762 1097 1494 1951 125 0.494 1.98 7.90 31.6 126 284 506 790 1138 1549 2023

Values in the chart are taken from the compressed Air and Gas Handbook, published by the Compressed Air and Gas Institute, 2130 Keith Building, Cleveland, Ohio 44115. Chart is based on 100% coefficient of flow (theoretical).

For well rounded entrance multiply values by 0.97. For sharp edged orifices with abrupt entrance, a multiplier of 0.65 may be used. All values are calculated, and are approximate. They are intended for estimating purposes only.

Vacuum Flow Through Orifices

Figures in the chart are estimated SCFM air flows through the influences of vacuum.

 Vacuum, Inches Hg. Orifice Diameter in Inches 1/64 1/32 1/16 1/8 1/4 3/8 1/2 5/8 3/4 7/8 1 2" 0.018 0.074 0.300 1.20 4.78 10.8 18.1 30.0 43.0 58.8 76.5 4" 0.026 0.100 0.420 1.68 6.74 15.2 27.0 42.2 60.6 82.6 108 6" 0.032 0.128 0.517 2.06 8.25 18.5 33.0 51.7 74.0 101 131 8" 0.037 0.148 0.595 2.37 9.52 21.4 38.5 59.5 85.3 116 152 10" 0.041 0.165 0.660 2.64 10.6 23.8 42.3 66.2 95.2 130 169 12" 0.045 0.180 0.725 2.89 11.6 26.0 46.3 72.6 104 142 185 14" 0.048 0.195 0.780 3.12 12.4 28.0 50.0 78.0 112 153 200 18" 0.055 0.220 0.880 3.53 14.0 31.8 56.5 88.0 127 173 225 24" 0.063 0.250 1.00 4.04 16.2 36.4 64.6 101 145 198 258

This chart shows estimated flows through a practical orifice, and are about 2/3rds the theoretical flow calculated for a perfect orifice.

The chart may be useful in estimating the flow capacity of a vacuum pump used to furnish vacuum to grippers used in handling sheet material used in the packaging, printing, and similar industries.

Please remember these values are approximate, as many other factors in the system would cause variations in flow.

© 1988 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.