Current values for motor-pumps with outgoing not open 100%
Current values for motor-pumps with outgoing not open 100%
(OP)
Does the current decrese or increse at a centrifugal pump if the outgoing is not open 100%. For exemple one valve is not open enough. Why? Thank you!





RE: Current values for motor-pumps with outgoing not open 100%
Ask yourself if the pump needs more power or less power with the valve closed. It has nothing to do with the motor.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Current values for motor-pumps with outgoing not open 100%
* for a radial flow centrifugal pump, opening up on a system throttle valve will increase BHP demand and current draw.
* for an axial flow centrifugal pump, opening up on a system throttle valve will decrease BHP demand and current draw.
* for mixed flow centrifugal pump, the curve is non-monotonic. As a very rough thumrule peak BHP is near BEP so current increases when adjusting flow in a direction toward BEP.
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RE: Current values for motor-pumps with outgoing not open 100%
RE: Current values for motor-pumps with outgoing not open 100%
The most common type of centrifugal pump in my experience would be radial flow and as electricpete points out above, closing a valve on the discharge would decrease both flow and amps drawn by the motor.
This may not seem correct, since as you say, pressure increases inside of the pump, but power requirements are closely related to fluid flow through a pump of this type and a throttling valve will decrease flow if it is partially closed.
Other types of pump will behave differently!
RE: Current values for motor-pumps with outgoing not open 100%
Look at BHP vs flow here:
http://www.gouldspumps.com/cpf_0009.html
You'll see for radial flow, BHP increases with flow and so current increases with flow.
You'll see for axial flow, BHP increases with flow and so current increases with flow.
Again mixed flow is trickier.
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RE: Current values for motor-pumps with outgoing not open 100%
Your belief is not correct for centrifugal pumps (or fans). If the flow is restricted for centrifugal pump outlet, there is lesser flow, the head remains constant so net power decreases.
This is not true for a positive displacement pumps.
Look up some basic text books on centrifugal machines.
RE: Current values for motor-pumps with outgoing not open 100%
Here, lets try it!
Here is the simple straight forward setup. It's a magnetic drive pump. An 1100gal/hr Little Giant.
A standard schedule 80 bulkhead was used and all piping and the ball valve are 1 inch which is the same as the pump inlet and outlet.
Close up of the pump.
A close up of the excellent wattmeter that was used.
The unrestricted bulkhead fitting.
Here we go. 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. And magnetization current.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Current values for motor-pumps with outgoing not open 100%
You get the award for going the farthest to prove a point in this forum!
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RE: Current values for motor-pumps with outgoing not open 100%
Keith Cress
kcress - http://www.flaminsystems.com
RE: Current values for motor-pumps with outgoing not open 100%
So to sum it up, it would that pump hp is more related to water flow through the pump than it is the pressure in the system?
RE: Current values for motor-pumps with outgoing not open 100%
RE: Current values for motor-pumps with outgoing not open 100%
Pump power is always proportional to Head(pressure)* Flow.
The centrifugal machines do not keep developing head (keep pushing)if there is no flow or restricted. Just inherent characteristic.
It's not the case with positive displacement pumps as davidbeach indicated.
RE: Current values for motor-pumps with outgoing not open 100%
Thanks for itsmoked experiment.
RE: Current values for motor-pumps with outgoing not open 100%
I dare you to do that experiment without any water in the can.
RE: Current values for motor-pumps with outgoing not open 100%
RE: Current values for motor-pumps with outgoing not open 100%
I would but the those mag-drive pumps are destroyed in seconds by pumping air.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Current values for motor-pumps with outgoing not open 100%
RE: Current values for motor-pumps with outgoing not open 100%
Anyhooo, it was a good demo.