pump position relative to flow tank
pump position relative to flow tank
(OP)
I have a 1.5 Hp centrifugal pump and I want to use it to move water through a tank to create a piece of test equipment for a flow-meter design. My question is, "Am I wrong to position the entire pump BELOW the tank?" In other words the suction port would take water downwards from one point in a 3'deep tank and force it directly upwards at another point, creating a boiling surface that was moving at a pretty good rate of speed. Would this work, or maybe be bad for the pump?
Peter
Peter





RE: pump position relative to flow tank
RE: pump position relative to flow tank
RE: pump position relative to flow tank
But back to your question, basically there is no problem with the supply level being above the pump inlet - in fact this is a prefered method of supply to the pump inlet.
As for pumping back into the bottom of the tank - this does not represent any problem either.
The only problem I can see at this point without having all your data available is that the return flow into the tank does not directly impinged on the inlet flow - direct the return flow away from the inlet flow as unstable flow to the inlet could result in performance problems.
Naresuan University
Phitsanulok
Thailand
RE: pump position relative to flow tank
You can visit the following sites for a good understanding on pumping systems
www.mcnallyinstitute.com
www.fluidedesign.com
www.pumpworld.com
Scipio,
Minimum submergence required to avoid vortexing can be calculated by the formula(I think this holds good only for water)
S = D + 0.574Q/D1.5
Where S is submergence in inches,
D is inner diameter of suction bell in inches and
Q is flowrate in USGPM
Reards,
RE: pump position relative to flow tank
Thanks for your good response. I suppose it's a slight semantic question as to the meaning of "suck." When a baby "sucks" (from his/her mother), he/she lowers the pressure inside the mouth using tongue and mouth muscles, and by your corrective reasoning, atmospheric pressure forces the milk into the baby. Hey...but of course! Taking atmospheric pressure into consideration is a unique and novel way of viewing early childhood.
Quark---
The setup is "weird" in order to make for a smoothly flowing water surface in the tank. Roughly square in profile---a polyethylene plating tank---the pump is discharging into the bottom at the lower left corner and drawing out of the bottom at lower right corner. The 3'depth of the tank dampens the fountain effect of the discharge and a series of plastic plates in the upper left corner smooths out the turbulence. The biggest problem is how to vary the flow from the pump, since it's an induction motor and it's difficult to make a variable speed control for an induction motor (that one can afford). Many thanks for the websites.
Scipio---
Thanks much for the formula. I'll check it out.
RE: pump position relative to flow tank
Regards checman
RE: pump position relative to flow tank
What is the estimated thru-put of the pump under your run conditions?
As for flow control, you could throttle the pump discharge so long as you stay within the operating band of the pumps performance, although this will increase the water temperature at a greater rate over time.
Naresuan University
Phitsanulok
Thailand
RE: pump position relative to flow tank
Thanks for your thoughts. I'm somewhat relieved because of them. It's a 2.5"dia. propeller-driven flow meter that uses tiny rare earth magnets placed at 180 degrees, N and S poles, to make a near sine wave signal against a coil with a soft iron core. Your basic "magnetic reluctance" pickup.
Artisi---
I also appreciate your concern coming from so far away. The pump I have, discharges about 38 GPM at 100 feet of head. I can't quite tell what it can be expected to do with only around 5 feet of head. Yes, the tank is 8" wide, an odd shape but it's all I need to test out a propeller flow meter, run some data on it, and so forth. I may have purchased a pump that is too powerful for this particular system, I don't know.
RE: pump position relative to flow tank
That's a huge flowrate compared to what you need, you'll need a choke valve on the pump discharge to throttle the flow and make up the difference in head, otherwise the pump will run off the end of it's curve, which introduces all sorts of problems, assuming the motor doesn't overamp and trip out. For a centrifugal pump, you should start against a closed discharge valve, then open the valve to increase flow from zero. A globe valve will probably work the best for your application. You may also have temperature problems with the water, every time it passes through the pump it'll get hotter, and it looks like you'll completely exchange the water in that tank in a little under 6 minutes.
RE: pump position relative to flow tank
Is it a motor-pump? can you change motor, if 2 pole motor changing to 4 pole will reduce head by factor of 4 and flow by half.
It is unlikely you will have any overload problems - pumps of this size tend to be non-overloading.
Naresuan University
Phitsanulok
Thailand
RE: pump position relative to flow tank
Regards,
RE: pump position relative to flow tank
RE: pump position relative to flow tank
If I understood the query rightly, I was thinking more in the lines of putting the meter under a constant hydrostatic head (water level) maintained, for example, by using overflows. The downward flow going to a receiver on which the collected water rate can be measured for meter calibration, and returned to the existing "prismatic" tank by a pump, if so desired. How far am I from the original "correct" idea ?