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Hydraulic Pump Stalling under load


dtesrgh

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Hello all, I am hoping you guys can help me troubleshoot my press.  My pump is a 16gpm log splitter purchased from Surplus center.  Unfortunately the tech I got hooked top with was zero help. (and I do mean zero) Below is a copy of one of my emails to them that describes my system.  Im stumped and would like new eyes on it before I change out my pump.  (and thats where im leaning to as the issues now)

The pump will stall out and lock my motor under any load of around 2 seconds.  Regardless where my pressure relief is set.  A little about my system.
Its all new.  My motor is 7.5hp 3ph spinning at 3600rpm.  All my lines are 1/2” and return to a 1” manifold with a filter rated at 50gpm.  My pump sits directly in front of my 20 gal reservoir and is flooded.  When running in idle the pressure gauge before my valve barely reads pressure so I know its flowing.
 
I can slowly bump this pump up to 2500 and it wont stall and stayed pressed.  But if I just let the pressure continuously build, it will quickly bog down and stall the motor.  Even at pressures of only 1500.  I have backed out the adjustment for the Hi side to the point where is wont stall but thats a max of 1300 psi.  And increase of adjustment from here will start to stall the pump.
 
Hope someone can help.  Thanks! 
 
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Read your post again.

Your math says it all.

General rule of thumb for hydraulic engineering: 1 hp per gallon @ 1500 psi. 

Your pump is way too big for your motor. 

At 1500 your pump would require 16 hp to not stall. 

At 2500 it would require over 25hp.

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Thanks for the quick replies, I appreciate it.

I have not heard that general rule and I will have to look it up.  I do know a similar sounding rule of 1gal of reservoir fluid for 1 gpm of pump.But that's completely different.  

I can tell you that your math works out to over three times the amount of power the pump manufacturer states is needed. (see attached pic).  This pump (and most all 16gpm log splitter pumps I have looked at) require 8hp min of GAS engine which is equivalent to around 5hp of electric power if you use the 3/5 rule of thumb from electric to gas.  In fact to confirm this I can also tell you my friend is running the same pump with 5hp electric with a 40ton cylinder and its a very capable press at 2500 psi.  So if anything, I have more power than I need for this pump.

Unless I am missing something?  Not trying to argue and the information is appreciated.  But I do know that these pumps are used all over in forging presses and do not have anything close to a 25 hp motor.

 

Screen Shot 2022-01-20 at 4.58.55 PM.png

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So I figured out your math error (I believe) and why they are rated the way they are.  The two stage pump kicks into high gear at around 700 psi and the gpm at that rate is approx 3.5 gallons.  If you look at the attached screenshot you'll see that 3.6gpm at 2500 requires only 6hp.  So its not my motor and I'm open to suggestions :)  

Screen Shot 2022-01-20 at 5.52.44 PM.png

Edited by Mod34
deleted duplicate text
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If your motor exceeds the manufacturer's requirements something else is going on.

I've never noticed a log splitter rated by GPM. Sure it's a factor but not something to advertise. Tonnage and rarely Inches/second travel I've seen. Never GPM, I'd think of an analogy but it wouldn't be helpful. 

When I see a hydraulic system rated by GPM it's to denote the speed of the system, NOT how hard it pushes, pulls, etc. 

Frosty The Lucky. 

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13 minutes ago, Frosty said:

If your motor exceeds the manufacturer's requirements something else is going on.

 

Yep, thats why I'm here ;)  Complete log splitters are probably not rated by GPM, but all the pumps are.

Thanks Frosty 

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Too bad you didn't say it was a 2 stage pump in the OP.

Thanks for wasting my time, glad you think it is funny.

Your pump isn't switching into low gallon hy-press, correctly. 

I would still like to see a picture.

Also what is your source for 3 phase?

 

 

 

 

 

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Sorry for your confusion. Log splitter pumps are two stage pumps and I did clearly state that it’s a log splitter. Anyone who has built a hydraulic forging press would be aware of this.  I was also quite polite I believe. I also stated that I believed the pump itself is the problem, but wanted hopefully get a second opinion by someone that has actually built their own, and therefore understands the components involved. 
 

im quite capable of using Google as well.  I am going to replace the pump. 

Edited by Mod34
Excessive quoting
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Happy New Year Matt,

The problem with having helpful discussions regarding a project YOU are working on, NOBODY can see what you are looking at or see the configuration you have. Remember that 'ASSUME' breaks down to, 'An Ass out of you and me'. Hydraulic problems are best sorted out with pressure gauges at the specific connections in question. To see if the 2-stage hydraulic pump is working proper, you MUST be able to visualize the pressure changes.

Being angry at someone you have never met before, has no gain. The keyboard is not a good tool, to convey expression.

Good Luck sorting out your problem.

Neil

 

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