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Author Topic: What happens if you run a hydraulic pump in reverse?  (Read 10202 times)
jraef
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« on: August 09, 2006, 02:36:41 PM »

I'm not an expert in hydraulics, but I'm trying to help someone with a perceived electric motor problem on a hydraulic pump, and I think that maybe he connected the motor leads without checking rotation and ran it in reverse. What would happen? This is an in injection molding machine.
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fluidpower1
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« Reply #1 on: August 09, 2006, 03:58:58 PM »

It would try to pump oil from the circuit and put back in thr tank. After the circuit is evacuated the pump continues to run it would run dry until it overheated and locked up mechanically if the clearances of the running parts are minimal.

Some Vane pumps with the Vanes in the Rotor at an angle could possibly bend, break, break segments out of the Rotor etc. until the pump locked up.

If it is running reverse rotation and someone hooked up the inlet to the circuit and the outlet to tank it would pump oil though it would probably cavitate due to the small size port connected to tank. However, when pressure starts to build most design pumps would blow the shaft seal.

An axial piston or bent axis pump would only make noise since the notches in the valve plate would be on the wrong side and each piston could have some high pressure spikes as it discharges its last bit of oil. However, thes pressure spikes wil reduce pump life in relation to max pressure setting.
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Bud Trinkel
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TWControls
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« Reply #2 on: August 09, 2006, 06:40:32 PM »

Just to add to this question, is there any rules of thumb for determining which way the pump should be rotating when it is not marked?
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TW Controls

"It's a lot easier to find another job than to find another family. And families tend to be a lot more loyal than corporations." - Steve Bailey
jraef
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« Reply #3 on: August 09, 2006, 06:51:50 PM »

Thanks for the reply.
Forgive my ignorance, but do hydraulic systems such as are used on injection molding machines typically have check valves? I was thinking that if reverse flow was being restricted or prevented in the fluid piping system, the pump would almost immediately cavitate and/or the motor would be seeing locked rotor amps. Am I all wet on that (pun intended)?
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maytag
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« Reply #4 on: August 09, 2006, 07:34:25 PM »

Most hydraulic pumps will rotate CW (looking at the shaft ) there are exceptions-the manufacturers ID tag and product catalog or the web can shed some lite if there is doubt.  Maytag
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fluidpower1
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« Reply #5 on: August 09, 2006, 08:18:19 PM »

jraef;

If you mean check valves on the suction (inlet) line, not normally. A suction line on a typical system that depends on atmospheric pressure to push oil into the pump should have no unnecessary restrictions that increase pressure drop. Atmospheric pressure at sea level is only 14.7 PSI on an average day and most pumps start cavitating at about 3 PSI negative pressure. Throw a check valve in and you increase pressure drop even if you take the spring out.

Went to a customer once where a check valve with a 5 PSI spring was installed in the suction line and he couldn't figure why the pump was so loud and din't last very long.

On pump rotation, as maytag said Clockwise or often called Right Hand rotation is normal off the shelf and since most pumps are turned by 3 Phase electric motors it is easy to make the motor turn the right direction.

One application that always requires a  Left Hand rotation pump is when a double shafted electric motor is driving two pumps. Most gear and vane pumps are field changeable to either rotation. Many piston pumps require a different valve plate to operate properly.
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Bud Trinkel
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There is one thing worse than being lost; its being lost and no one is
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- Chuck Kelley, president, New Orleans Baptist Theological Seminary
fluidpower1
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« Reply #6 on: August 09, 2006, 08:30:49 PM »

Determining pump rotation on a Gear pump is the simplest one.

The drive shaft is offset since it is driving one gear  direct and they normally have a lrge Suction port and a smaller Outlet port. Since flow in the pump is between the gear teeth and housing it is easy to imagine which way the pump is setup by turning the shaft so flow is from the large port to the small port.

Gear pumps are most often the ones that have no markings for rotation.

Also some gear pumps made for Mobile equipmet have two large ports and can turn either rotation. The correct port must be connected to tank and the other port could be reduced since it will then be outlet.

These pumps have check valves in their housing to keep outlet pressure from going to case and blowing the shaft seal while bypass oil can get back to the suction port.
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Bud Trinkel
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www.fluidpower1.us

There is one thing worse than being lost; its being lost and no one is
looking for you.
- Chuck Kelley, president, New Orleans Baptist Theological Seminary
jraef
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« Reply #7 on: August 10, 2006, 10:59:02 PM »

Thanks for the info. The person in question apparently did not know that just because he marked the wires when he removed the machine that it wouldn't necessarily rotate in the same direction when he installed it at a different plant. He says he didn't check for rotation because he just hooked everything up the same way it came out (he's not an electrician).
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TWControls
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« Reply #8 on: August 11, 2006, 04:45:10 PM »

Yes thanks for the tip Bud
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"It's a lot easier to find another job than to find another family. And families tend to be a lot more loyal than corporations." - Steve Bailey
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