keltrem

Tim88, In a discussion with Hydraulic engineers yesterday we addressed that point. It is not a big issue for us as we require a specific flow rate within a narrow range of tube length plus flowrate can vary within an optimal range giving ample allowance for resistance.

Studiot, The purpose of the OP was to ascertain whether or not there is a calculation or formula that provides a relationship between pressure and flow rate. I now know there is. if I wanted a specific answer to our problem I would have noted the liquid and other relevant data. I deliberately did not do this . The engineering development group we are dealing with seem all at sea when trying to resolve this question which has caused undue frustration. Gratuitous advice as above is not helpful either. From the responses on this forum, not yours Studiot, it is now apparent we need to change Consulting Engineers who better understand pressure and flow. To all other posters thank you, it has provided certainty of direction.

What I am trying to find a solution for is this. A production unit to operate at its optimum requires a flow rate within a specific range of +/- 10% of its optimum flow rate (which is known). We want to install a delta pressure valve to to ensure that the unit is only operable within the specified parameters. We need to calculate the minimum and maximum pressure to achieve the desired operational minimum and maximum flow rates. All other information is available to us; flow rate, viscosity, pipe diameter, length of pipe (this is only relevant to the extent within the confines of the pressure valve). I reviewed the Hagen-Poiseuille equation but it seems to me to only calculate pressure loss. Any further guidance would be much appreciated.

If all factors including viscosity, pressure, diameter of tube are known how is flowrate calculated?

Is it possible for a known pressure and diameter of tube that liquid flowrate in litres per sec (for example) can be calculated? If so what data is necessary for calculation and what is the formula? Thanks, Noel

We are conducting a trial of a process on liquid full cream milk. Control and trial samples are held for analysis on a two day continuous cycle with an unopened sample used for each test. One of the tests is Standard Plate Count. On review of the results we do not understand why there are such wide variances in results between samples tested For example; Result one in test/date order (cfu's) Each successive result is milk two days older than the previous test. The testing facility is an accredited milk analysis laboratory. 7,000 600,000 3,000 2,200,000 160,000 41,000 15,000,000 What explanations could be applied to these results?