Gear pumps and volumetric efficiency
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The actual output speed value (RPM) of the gear pump [with variable frequency reduction] is divided by the actual outlet flow rate (m3/h) by [volumetric efficiency]* The theoretical flow rate of the pump (CC/rev)] can be obtained ； So please: Are the maximum, minimum and normal output speed values the same as the volumetric efficiency? That is, whether: Is volumetric efficiency a fixed value? Does it remain unchanged within the range of minimum flow rate to maximum flow rate? If not, how to find the maximum output speed value? Please let the experts answer, thank you!
Reply 1# fafa_ma Judging from your calculation formula, the volumetric efficiency can be a changing value. In fact, it is also a changing value, mainly related to the pressure difference between the inlet and outlet. If the pressure difference is large, the volumetric efficiency is low. If the inlet and outlet pressures are relatively stable, then the volumetric efficiency can be treated as a fixed value when calculating the speed when the flow rate is variable. There should be recommendations for this value.
Reply 2# majing* What an said on the 2nd floor makes sense. What I'm actually more confused about is: The data table we got is defined like this: Maximum output speed value = maximum flow rate/(theoretical flow rate * Maximum volumetric efficiency); minimum output speed value = minimum flow rate/(theoretical flow rate * minimum volumetric efficiency). This definition is difficult to understand. Why is there a negative correlation between the maximum output speed and the maximum volumetric efficiency? If the minimum volumetric efficiency is taken, wouldn't the obtained value be larger? Puzzled. Keep asking for advice, thank you!
There is some gap between the gears of the gear pump (the material will partially flow back), the pressure difference between the inlet and outlet is large, and the volumetric efficiency is low. In general, the load is large, the speed is high, the pressure difference between the front and rear is relatively large, the material backflow is large, and the volumetric efficiency is low. Therefore, the maximum output speed has a negative correlation with the maximum volumetric efficiency.
Speed and volumetric efficiency do have a great influence, but high speed, high pressure and high reflux will increase； However, the proportion of low-speed return flow in the overall flow will also increase, and the efficiency will also be greatly improved, because the gap will not change with the speed.
This post was last written by majing* an edited reply 3# fafa on 2010-8-30 16:16_ma In fact, there is something wrong with your formula expression. Let me rewrite the formula and you will understand. Actual speed/speed corresponding to theoretical flow = theoretical flow corresponding to actual speed/theoretical flow = (actual flow/volume efficiency)/theoretical flow. Note: The left side of the original formula omits the "speed corresponding to theoretical flow", which is the base speed for your speed regulation. On the right side of the formula, put the efficiency in the denominator and it will be the same as your formula. "Maximum flow" corresponds to "maximum volumetric efficiency", and "minimum flow" corresponds to "minimum volumetric efficiency". This efficiency may not necessarily be the maximum/minimum value, which may be easier to understand.