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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

Hydraulic pump getting weak?? Liebherr 932 Excavator

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04-29-2012 15:31:57

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Hey all, quick question, is there a way I can test the hydraulic pump on my Liebherr 932 excavator to see if it"s operating at the right pressures or whatever? Or is there a special tool for that. The machine seems sluggish for some reason. Every filter on it is new as I just serviced it. I was digging the other day and it just seems a lil slower than it should be. All hydraulic functions. The machine is an older one, early 90"s, I dont recall the exact year. Anyhow, just wanted to see if anyone here might have a suggestion I could try. Thanks!

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05-01-2012 01:26:52

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 Re: Hydraulic pump getting weak?? Liebherr 932 Excavator in reply to Case450, 04-29-2012 15:31:57  
I'm not sure if the Liebherr machines sold in the US are the same as what is sold here in the UK,the machines here have a couple of different work modes and a heavy lift,in the heavy lift mode the flow from the pump is reduced,the hydraulics slow up and the lifting capcity increases,as far as I remember there is a switch on the panel with a heavy weight symbol,when it is lit up heavy lift mode is engaged,if you have a handbook look up the different work modes,in the right digging mode when a lever is touched there is a rapid responce fom the engine tone,if you are not getting that response in digging mode it could be the main regulator valve has an issue,the pumps are fairly robust and though I have changed one or two due to other things causing the failure they are reliable.

Good luck


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04-29-2012 19:23:37

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 Re: Hydraulic pump getting weak?? Liebherr 932 Excavator in reply to Case450, 04-29-2012 15:31:57  
About the only way to test the pump is with a flow meter equipped with a load valve, a flow meter alone will not do the job. I say this because the pump may be pumping the required GPM at a low pressure but as the pressure rises flow bypassing in the pump, etc will cause the flow to drop off. I have tested excavator pumps that appeared good until I loaded them and at that point the flow slowly went away to nothing, or nearly so.

That said, as bad as I hate to tell you this, there is no way for you to test the pump yourself without spending a fair amount of money on a flow meter with an integral load valve, or a simple, inline meter with a needle valve to use for loading. Either will work but the ones with the integral load valve typically also have a rupture disc as a safety feature in case the load valve is closed too far. I have had pumps that were sticking and as I shut down the load valve they would suddenly unstick and increase the flow more than the meter could handle valved off thar far, and they would rupture the disc to allow the excess flow pass. Like I said, using the inline ones, with a needle valve inline downstream of the meterto load the system will work but it's just not as safe when used on something like an excavator pump that has a variable/pressure compensated flow.

As someone who does this kind of thing for a living, ultimately the best advice I can give you is to call someone who knows what their doing, and has the right equipment to do the job. Good luck.

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04-29-2012 18:34:20

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 Re: Hydraulic pump getting weak?? Liebherr 932 Excavator in reply to Case450, 04-29-2012 15:31:57  
Preasure equals strenth of the work or machine..Flow on the other hand equals speed of the work performend. You will need a good high flow flow meeter to determine if the pump is putting out the recomended flow for the model machine. A small guage capable of measuring 4,000lb preasure will check the relief valves but again all that will tell you is the strength of the machine. Normaly weak or worn pumps show up after the hydraulic fluid warms up. Check the fluid to make sure it is not over heated.

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04-29-2012 18:51:22

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 Re: Hydraulic pump getting weak?? Liebherr 932 Excavator in reply to jm., 04-29-2012 18:34:20  
So during operation the hydraulic fluid should be warm? hot? do i take a temperature reading of the fluid in the resevoir?

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