McElroy Discussion Forums

28 pump pressure
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Author:  scotian [ December 13th, 2010, 2:00 pm ]
Post subject:  28 pump pressure

I have a customer with a rolling 28 and the hydrualics are causing problems. The main pressure can not be adjusted over 280psi. The relief valve has not been tampered with. They also say the facer is moving very slow. Is the pump shot?

Author:  tulsamurph [ December 13th, 2010, 4:10 pm ]
Post subject:  Re: 28 pump pressure

The pump may be at fault, but let's see if there are other possibilities.

We will assume that the voltage is sufficient.
Check to make sure that the shaft on the motor and/or pump are not slipping inside the coupling.

Does the gauge appear to be functioning correctly? Sounds like it is since the facer is turning slowly.

Try checking the pressure with the carriage disconnected, *and the facer turned off. Does the pressure come up? If so, there may be a bypass problem in the carriage hydraulics.

If the pressure still does not come up, remove the pressure relief valve and check for damage. Also, make sure the filter is not clogged, and the inlet is not restricted.

In the event that the adjustment on the pump has been changed at some point, it can be adjusted as follows:
With the pump running and nothing moving, (*Facer off,) the pressure should be 900 psi.
When the carriage is in motion, *at fusion pressure, say 220psi, the pressure should drop to *approximately 300 - 325 psi or so.
When the facer is running, pressure will usually be close to 300 psi.
The adjustment nut does not adjust pressure, only the shift point at which the pump shifts from low flow to high flow.
The pressure relief valve should be used to set system pressure.

*When you try to adjust the pressure relief valve, with carriage disconnected and facer valve closed, does the pressure respond at all?

Any unusual smells, sounds, or temperatures? (Hydraulic fluid hot, burnt, sludge, etc.? Rattles, knocks, etc.?)

If the rest of the system is sound, and the pump is spinning at the proper speed, the pump is at fault.

Please keep us posted as to your findings.


*=Edited part of this post

Author:  scotian [ December 14th, 2010, 1:36 pm ]
Post subject:  Re: 28 pump pressure

The pump is putting out good flow (4.5 GPM roughly). Could the pump not be switching stages?

Author:  tulsamurph [ December 14th, 2010, 2:59 pm ]
Post subject:  Re: 28 pump pressure

Yes, that certainly is possible. Have you tried to adjust the shift point to see if you can get it to change? If the pump is not shifting, it would have to be replaced. Do you have an idea of how old this machine is?

*Edit* It is likely that if the motor were not switching stages, it would trip the circuit breaker in the motor circuit. Have you had this issue?

Thank you,

Author:  tulsamurph [ December 14th, 2010, 6:17 pm ]
Post subject:  Re: 28 pump pressure

Please note the changes in my trouble shooting post. It is more accurate now, and may clarify some points.

Thank you,

Author:  scotian [ December 15th, 2010, 7:23 am ]
Post subject:  Re: 28 pump pressure

They inform me that the motor has been tripping the breaker.

Author:  tulsamurph [ December 15th, 2010, 6:15 pm ]
Post subject:  Re: 28 pump pressure

Have you tried adjusting the shift point? Do you know how frequently it is tripping the breaker?


Author:  jgeschke [ July 12th, 2012, 12:48 pm ]
Post subject:  Re: 28 pump pressure

Where is a good starting point on the Hi-Lo adjustment. :?: I run across this problem quite often where the unti is pulling high amps, tweek down the Hi-Lo to where I think it should be good, then create another problem... Like this AM where all of a sudden, had 0 pressure when facing.. Started adjusting Hi-Lo back up, heard it shift & then started bogging. Played with it some more to where I think it should be good but who knows? :evil:

Is there a good standard procedure to follow in such a case?

Author:  Matt [ July 13th, 2012, 8:33 am ]
Post subject:  Re: 28 pump pressure

The 28 hyd pump is a hi-low gear pump. This means that it will run high pressure and a low flow for fusing the pipe, when the facer is turned on the pump shifts to a lower pressure and a high flow to facilitate proper facer speed.
This adjustment is set under the acorn nut on the side of the pump.
First make sure your system pressure is set at 900psi.
Turn the facer on, with the facer running your system pressure should drop to 300psi.
If not,
Remove the acorn nut.
Loosen the jam nut,
Adjust set screw until you have 300psi with facer running.
Tighten jam nut.
Verify 900psi with facer off, turn facer on and watch for the drop of system pressure to 300psi.
If your pump has been operated with system pressure set below 500psi, with out the facer running, you could possibly have cavitated your pump.

Author:  jgeschke [ July 13th, 2012, 10:47 am ]
Post subject:  Re: 28 pump pressure

In response, we rec'd this unit back from a customer whom had adjusted both the pump setting under the acorn nut & the main pressure setting at the gauge. Have no clue where we are at... What is a good starting point so as not to cause further damage? :?:
Should both adjustments be backed out, turned in, or maybe somewhere in between?

Author:  Matt [ July 16th, 2012, 7:12 am ]
Post subject:  Re: 28 pump pressure

First make sure the setting under the acorn nut is turned out a few turns (if you turn the screw in too far it will make contact with the gears and ruin the pump).
Then set your system pressure.
From here follow the instructions from my previous post.

Author:  Joshua [ November 19th, 2013, 4:06 pm ]
Post subject:  Re: 28 pump pressure

This came up again so I thought I would reiterate the procedure for setting the system pressure and the pump adjustment under the acorn nut.

A. Remove cover nut from the pump adjusting screw. Loosen lock nut and back screw out until very little tension is felt on the screw.
B. Back relief valve adjustment out to zero pressure.
C. Jog motor to fill pump and lines with oil before start up. (if this is a rebuilt unit being started for the first time)
D. Start motor and adjust relief valve to 900 psi.
E. Using the selector valve, set the fusion pressure to 600 psi, facer pressure to 100 psi (or as low as possible) and heating pressure to 125 psi.
F. Open the facer valve and make sure the pressure on the relief valve with the facer running is 300 psi. Adjust the pump adjustment screw with the facer running to set this pressure. Tighten the lock nut and replace the cover nut on the adjustment screw.

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