Submersible Pump Motor Application
Submersible Pump Motor Application
(OP)
Hi all,
I am new to this forum and basically new to my job trying to learn about hydraulic elevator systems. We use submersible pumps with submersible motors to drive a piston which does the actual lifting of the elevator.
My question is how motors are sized for pumps. From gross weight and desired speed of lift in FPM, we can get required GPM. and from a pump table I can see that HP for a certain pump at 350 PSI and 185 GPM is 46.5.
Does this mean that the pump will supply 46.5 HP at 350psi and 185gpm? and that I would have to use a motor of at least 46.5 HP capacity? Would I also have to match torque requirements?
If I used a 40HP motor what would happen?
If I used a 60HP motor what would happen?
Anything anyone would like to share would be great. As you can see I'm a newbie.
Thanks!!
I am new to this forum and basically new to my job trying to learn about hydraulic elevator systems. We use submersible pumps with submersible motors to drive a piston which does the actual lifting of the elevator.
My question is how motors are sized for pumps. From gross weight and desired speed of lift in FPM, we can get required GPM. and from a pump table I can see that HP for a certain pump at 350 PSI and 185 GPM is 46.5.
Does this mean that the pump will supply 46.5 HP at 350psi and 185gpm? and that I would have to use a motor of at least 46.5 HP capacity? Would I also have to match torque requirements?
If I used a 40HP motor what would happen?
If I used a 60HP motor what would happen?
Anything anyone would like to share would be great. As you can see I'm a newbie.
Thanks!!





RE: Submersible Pump Motor Application
RE: Submersible Pump Motor Application
RE: Submersible Pump Motor Application
As for torque requirements, yes, you have to meet them, but on a pump like this it's usually not much of a problem, the startup torque is frequently the highest torque requirement due to machine inertia, however it's not that high in these pumps. It's easily enough checked by requesting torque vs. speed curves for both the pump and motor from 0 to 100% of full load speed.
If you put a 40 hp motor in there, it would likely run for a little while if it had a high enough service factor, but within a few months you'd likely be replacing the motor - they tend to overheat and burn out prematurely if you run them that high.
If you put a 60 hp motor in there you're fine - you might be wasting a few bucks as a 50 hp motor would likely work fine though. Easiest way is just to ask the vendor what the rated and maximum horsepower requirements are for the pump, and make them responsible for putting the right motor on to cover the entire operating range.
RE: Submersible Pump Motor Application
RE: Submersible Pump Motor Application
Regards
Dave
RE: Submersible Pump Motor Application
The type of curve CESSNA1 describes is usually catalog info covering the hydraulic envelope a particular pump model & size can handle, or in the case of a variable speed unit a family of speed curves. If, however, you have a fixed speed pump and you have a specific model & size selected, a more specific curve can be generated. The specific curve will usually show flow vs. head, along with power requirements across the capacity range, at rated speed. If you know the horsepower requirements and the speed at a given point, you can calculate the torque.
I'm assuming you're probably looking at a gear, vane or lobe pump here, in which case I wouldn't worry about the torque. Startup torque is usually the only place you run into problems. One example is a progressing cavity pump - these operate with an interference fit between an elastomer stator and a steel helical rotor. Since the static coefficient of friction is greater than the dynamic coefficient, more torque can be required to overcome the static friction between the two and get the rotor turning than is required to keep it turning. Another example could be a large multistage centrifugal pump where the rotor is massive enough to have a significant moment of inertia resisting accelerating up to speed. The type of pump it sounds like you're looking at shouldn't have any of these concerns associated with them, but the vendor should be able to tell you for sure.
As for what's required to get the elevator cab moving, sorry, that's something I have no experience whatsoever with, I don't know what your startup scenarios would be.
RE: Submersible Pump Motor Application
Naresuan University
Phitsanulok
Thailand
RE: Submersible Pump Motor Application
FYI:
Pump curves are typically based on fresh water. If you are using hydraulic fluid you need to talk with the pump manufacture. Hydraulic fluid is usually a low viscosity, but head degradation does occur due to viscosity.
HP curves are also based on fresh water. If the pump curve predicts 46 HP, that number is most likely base on fresh water. HP is a liner calculation based on fluid specific gravity.
About Pump Torque Curves:
I have personally never seen a pump torque curve; however a pump manufacture can provide you with pump inertia information for a given impeller. For your needs you could look at the motor speed torque curve and predict the RPM developed under given load conditions for that motor. You can then compare the motor slip to the pump curve and make a more accurate load calculation. Manual iteration between the two curves could take hours or days to complete, but HP required will change approximately at the cube of the speed change. I sell oil filled motors that are a little different than most motors you will encounter. For our motors I wrote a Y equivalent spreadsheet that makes these calculations for me.
This is a little late, but hope it helps some!