Simple question about motor current draw and power
Simple question about motor current draw and power
(OP)
I'm wondering about the current draw from a constant speed pump motor. If the discharge control valve from a pump discharge is throttled more, would that make the motor draw more current and therefore increase the power? Or is the motor taking constant current regardless of what is happening with the discharge control valve?
Thanks
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RE: Simple question about motor current draw and power
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RE: Simple question about motor current draw and power
RE: Simple question about motor current draw and power
RE: Simple question about motor current draw and power
RE: Simple question about motor current draw and power
So assuming that when you first said "If the discharge control valve from a pump discharge is throttled more..." you meant throttled DOWN, as in closed off more, then the motor current would in fact go DOWM as the Q is reduced.
RE: Simple question about motor current draw and power
RE: Simple question about motor current draw and power
BTW are you sure the hydraulic pump isn't positive displacement though? I'm not sure how you could ever get 3,000psi out of a single stage centrifugal pump!
I suspect it is a positive displacement pump and would indeed draw more current if throttled.
It could be a pump with a built-in relief valve. In which case it always puts out so much pressure and hence the relief valve(bypass)is always open and as the load is throttled the relief just carries more. This would not behave in the classical manner described previously.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Simple question about motor current draw and power
RE: Simple question about motor current draw and power
Methinks he was using the term "hydraulic" as in general liquid flow, not as in Hydraulic Power Unit.
RE: Simple question about motor current draw and power
Normally when you say "hydraulic" and "power" in the same sentence it means "hydraulic power equipment".
But that's cool.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Simple question about motor current draw and power
The system running with the ball valve wide open.
The pump is consuming about 100W of power doing maximum work, which is moving about 1100gals/hr of water. Note the solid column of water returning to the tank. 103.8W
Now for some throttling. The ball valve is about half closed.
Notice the flow has dropped substantially. Notice also the power has not risen. The pump is not working harder.. It is working LESS. The power has decreased. 72.7W
Now the valve has been closed about 25%. Power has dropped still further.
57.9W
Here I have closed completely, blocked, the flow. Notice the power has dropped further yet! Of course it is not zero as there is a fan being run, bearing friction is present. Windage is occurring in the motor. There is resistance in the windings and there is some recirculation occurring in the pump head. Over time - minutes - the pump head would get warm. If there was the slightest trickle of water allowed thru the pump there would be no measurable heating as water can carry a great deal of heat away.
47.7W
Keith Cress
kcress - http://www.flaminsystems.com
RE: Simple question about motor current draw and power
RE: Simple question about motor current draw and power
I kid.. but I did it in Feb. Funny how many times it has come in handy. It should be in any engineering text book that talks about pumps.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Simple question about motor current draw and power
RE: Simple question about motor current draw and power
A pure axial flow type pump (propeller type pump) behaves the opposite. Decreasing flow by throttling down on a flow favle increases the power draw over most of the range.
A multi-stage mixed flow pump can be a combination. Results depend very heavily on where you are on the range.
Rightly or wrongly, axial flow pumps are often called centrifugal (they follow the centrifugal pump laws).
So, I agree with Scotty: "it depends". Even if you are talking centrifugal pumps.
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RE: Simple question about motor current draw and power
RE: Simple question about motor current draw and power
When both fluids are set for the same flow and TDH from the pump, the power draw is higher with the denser fluid.
RE: Simple question about motor current draw and power
Keith Cress
kcress - http://www.flaminsystems.com