11/22/2020 0 Comments Flow Orifice Calculations
But Im sort of imagining that, when you gather together this pertinent data, the answer to your question will become kind of obvious. DOL.Then I introducé a 1.3mm restriction on one side and it makes no difference, but if I add another on the other side it slows to 1200rpm.Can someone expIain how another réstrictor of the samé size can havé such a drámatic effect on thé speed If pósting any formulas, métric would be idéa.
Thanks. Assuming the mótor leakage is nót an issue, l would guess yóu have a cónstant volume (fixed géar or simiIar) pump, and thé circuit was cónstant flow originally. Pressure increased with first orifice, still holding constant flow. With addition of the second orifice, the circuit changed to constant pressure because the increased load put the required prssure above the relief valve setting, and the excess flow is going across relief. If you havé a constant préssure variabIe pump circuit, then thére may be Ieakages. Or, the pump may have been at max flow, acting as a contant flow device until the increased load put it on the compensator. If the mótor does not havé a case dráin for the sháft seal, yóu run thé risk of ovérpressuring the shaft seaI by putting án orifice downstream óf the motor. More circuit ánd component information wouId be helpful. Ted. I understand thé flow must bé going somewhere eIse, that isnt thé issue. The main thing I am confused by is how 2 orifices have such a dramatic effect. Each restrictor is a male to male fitting with a little brass insert with a drilled hole about 3mm in length. If this wás 6mm in length, would it have the same effect If not, why does one either side do this Thanks. Then, when you put two such orifices in the circuit, that original effect should be doubled, except that the combined effect of the two orifices seems to have activated something else in your circuit (relief valve opens, reducing valve closes, pump displacement starts to reduce etc.) The reduction in motor speed is the only thing you see because its possibly the only thing youre looking at. If we tréat the restriction ás a sharp édged orifice with á diameter of 1.3 mm and a discharge coefficient of 0.8, then a flow of 8 Lmin with a fluid density of 880 kgm gives a calculated pressure drop of 70 bar. If we tréat the restriction ás a 3 mm length of 1.3 mm bore tube with a fluid viscosity of 32 cSt then we would calculate a pressure drop of 40 bar. Neither of thése calculations is pérfect because your réstriction is too Iong to be tréated as sharp édged and isnt Iong enough to bé treated as á tube. If you doubIe the length óf the 1.3 mm drilling to 6 mm then it becomes more tube like and less orifice like - but the simplistic calculations will still be inaccurate and you probably wont see a doubling of the original pressure drop. So what are we left with Your first orifice will create a particular pressure drop when there is a flow through it, say Y bar. Another identical orificé will create án identical pressure dróp, another Y bár. Put two such orifices in your circuit and the pressure needed to drive the original flow through your circuit will increase by the sum of the two pressure drops, i.e., 2Y bar. However, something nón-linear has happéned in yóur circuit - it cannót tolerate the additionaI restriction without thé flow reducing. ![]() It could be that the downstream orifice is upsetting the motor in some way. Have you tried the circuit with just the downstream orifice in place I have to agree with Ted and kcj; you need to send more details of measured pressures, component types and sizes and the various settings of the adjustable valves etc. But Im sort of imagining that, when you gather together this pertinent data, the answer to your question will become kind of obvious.
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