Flow through Orifices

Flow through Orifices

womackmachine.com

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 x 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
GPM3/641/165/643/327/641/89/645/3211/643/1613/647/3215/641/45/163/87/161/2
3544017307103331841086844302116129731– – –– – –
5– – –480019709255123001881238459433224198421
10– – –– – –– – –3700205012007504903362381721289775311585
15– – –– – –– – –– – –460027001690110075753438828821916969331811
20– – –– – –– – –– – –– – –4800300019681345950690513390300123593219
30– – –– – –– – –– – –– – –– – –6750443030252135155011558756752751357242
40– – –– – –– – –– – –– – –– – –– – –– – –53803800276020501555120549523512875
50– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –4310320524301880770370200118
60– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –4615350027051110535288170
70– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –476536851510725390230
80– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –48101970950510300
100– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –– – –30801480800470
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.

orifice plate installed in union
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.
orifice plug installed in a fitting
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.

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

Compressed Air Flow Through Orifices

PSI
Across
Orifice
Orifice Diameter in Inches
1/641/321/161/81/43/81/25/83/47/81
50.0620.2480.9933.9715.935.763.599.3143195254
60.0680.2721.094.3417.439.169.5109156213278
70.0730.2931.174.6818.742.275.0117168230300
90.0830.3311.325.3021.247.784.7132191260339
120.0950.3791.526.0724.354.697.0152218297388
150.1050.4201.686.7226.960.510816824232430
200.1230.4911.967.8631.470.7126196283385503
250.1400.5622.258.9835.98039144225323440575
300.1580.6332.5310.140.591.1162253365496648
350.1760.7032.8111.345.0101180281405551720
400.1940.7743.1012.449.6112198310446607793
450.2110.8453.3813.554.1122216338487662865
500.2290.9163.6614.758.6132235366528718938
600.2641.034.2316.967.61522714236098281082
700.3001.204.7919.276.71733074796909391227
800.3551.345.3621.485.719334353677110501371
900.3701.485.9223.794.821337959285311611516
1000.4061.626.4926.010423441564993412721661
1100.4411.767.0528.2113254452705101613831806
1200.4761.917.6230.5122274488762109714941951
1250.4941.987.9031.6126284506790113815492023

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 Diamter in Inches
1/641/321/161/81/43/81/25/83/47/81
2″0.0180.0740.3001.204.7810.818.130.043.058.876.5
4″0.0260.1000.4201.686.7415.227.042.260.682.6108
6″0.0320.1280.5172.068.2518.533.051.774.0101131
8″0.0370.1480.5952.379.5221.438.559.585.3116152
10″0.0410.1650.6602.6410.623.842.366.295.2130169
12″0.0450.1800.7252.8911.626.046.372.6104142185
14″0.0480.1950.7803.1212.428.050.078.0112153200
18″0.0550.2200.8803.5314.031.856.588.0127173225
24″0.0630.2501.004.0416.236.464.6101145198258

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.

To read about pumps, click here.


womackmachine.com

© 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.

idconadmin

idconadmin

EXPLORE BY TOPIC

Join the discussion

Click here to join the Maintenance and Reliability Information Exchange, where readers and authors share articles, opinions, and more.

Get Weekly Maintenance Tips

delivered straight to your inbox