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hydraulic pump mechanisme Question
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Posted by: snapper

07/06/2004, 01:51:49

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hi,

Please tell me how a variable displacement pump works. Because I have one and the type is AVSO4 - 250, and it has pumping failure. We use this pump for our pressing machine

We have brake down all the part and we found that the piston is crushed. I don't know how it happen and still searching for the cause. We also need to know is it normal to have a crushed piston.

I need a help on this one.

Thanks,

David







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Re: hydraulic pump mechanisme
Re: hydraulic pump mechanisme -- snapper Post Reply Top of thread Forum
Posted by: maytag

07/07/2004, 10:18:20

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You have a Rexroth axial piston pump with pressure compensated control as designated by the VSO.  Flow from the pump is directly proportional to the RPM and swash plate angle.  Press.compensated control is only 1of several control options.  There should be a pointer on the side of the pump that is marked off in degrees from 0 to 15-with 0 the pump having no flow and 15 degrees being maximun swash plate angle and max flow provided the RPM of the pump is maximum.  The pressure compensator controls the swash plate angle.  When system pressure falls below the spring setting of the compensator the pump comes on stroke to 100% flow and will stay in this condition until system pressure overcomes the compnsator setting and then will destroke the pump(bring swash plate back to 0 degrees-no flow )

Failure such as you have is no uncommon esp. if using fluid other than mineral oil or contaminated fluid-it will benefit you to either change the fluid in your system and clean the tank or filter it sufficiently before installing a new pump.  We use theses pumps and controls a lot where I work and sample the fluid monthly for particulates and water.  Hope this helps,Maytag







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Re: hydraulic pump mechanisme Idea
Re: Re: hydraulic pump mechanisme -- maytag Post Reply Top of thread Forum
Posted by: snapper

07/08/2004, 01:44:10

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hi, Maytag

Thank's for the information. According to your experience what kind of preventive maintenance will give the pump best performace beside to check oil cleaness.

Which one is better and efficient change the whole unit or just change the wornout part.

regards

David







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Re: hydraulic pump mechanisme
Re: Re: hydraulic pump mechanisme -- snapper Post Reply Top of thread Forum
Posted by: maytag

07/08/2004, 19:17:19

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David,Let me correct myself before I go any further-I looked in 1 of my books at work and the VSO is the model type-I was correct in that it is an axial piston variable displacement pump with a swash plate but the VSO does not tell us what control feature you have(whether it is pressure compensated or not, although if it is an older version I'd bet that is was pressure compensated.) Somewhere on the tag with the A4 VSO 250 you will have DR or LR or FR or some other 2 letter designation which tells us what control feature the pump has,but regardless they are all varying the swash plate angle to change pump flow.
AS far as rebuilding a pump,I would buy a rebuilt unit that has already been tested instead of attempting it myself. we have the facilities to rebuild but no way of testing our pumps that big so we exchange with our local distributor. In addition to monitoring the oil sample each month we have a flow meter in the case drain(this should be a 3rd line coming off the pump itself and running directly back to tank-probably 1 1/4 or 1 1/2 hose) a new or rebuilt pump should be about 95% efficient. At 1800 rpm you should have between 4-5 gal.per min.returning to tank via the case drain-so you can use this as a way to check the internal wear-more wear more wasted oil returning thru case drain. the higher the operating pressure and thinner the fluid the more fluid thru the case drain. Good luck,Maytag






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Re: hydraulic pump mechanisme
Re: Re: hydraulic pump mechanisme -- maytag Post Reply Top of thread Forum
Posted by: snapper

07/12/2004, 01:54:08

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Thank's Maytag.






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