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Hitachi EX27u Low Pressure ?

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Hitachi EX27u Low Pressure ?

Post #1 by le.maisonniau » Sat Jan 13, 2018 1:16 pm

Hi Guys,
I am in the middle of 'fiddling' with a mini digger I bought last summer, bought it 2nd hand in France, I knew at the time there would be lots of maintennance to bring it up to spec - and wasn't wrong.
So Far I have cleaned it all down so it is OK to work on, then drained all the emulsion that was passing for Hydraulic oil out of the tank, changed all the hydro filters, cleaned the suction filter and replaced it, replaced 4 pipes with new (2 x pecker and 2 x Boom)- serviced the track tensioners and idler wheels and got the tracks back on myself (quite easy :thumbup: surprisingly) and have been running the engine/pump slowly over the past week and exercising the rams - ran it up and down inside my woodyard (too wet outside) and the tracks seem really good now - lost the horrid squeak that was present when I bought it - even managed to get the m/c into "high speed" and seems good.

So, my current issue: To me it seems to be a pressure related problem that has me scratching my rear: :( The following tests are done with m/c at half revs.
The dozer blade will no longer lift the m/c of the ground :roll: OR the Boom will not lift the m/c off the ground; depending on whether the dozer blade is up or down :roll:
IF - the dozer blade is down, the m/c is unable push out the boom ram, if I lift the blade up -then- I get full action (pressure !! ) to lift the m/c up,
IF - the boom and dipper are all retracted in, this makes NO difference to dozer.
The dozer blade will, slowly lift up the m/c at half revs, if I push the lever, release push again etc. i.e. sort of teasing it up.

A mate of mine suggests replacing the seals inside the dozer ram !!! he is a supposed hydraulic expert :lol: and has in the past suggested putting washers behind the control leavers on my cherry picker to "boost" the pressure - So not a lot of confidence in his suggestion. He does however have hydro pressure testing meters and Tee's and is willing to help me test the system pressure.

1 Should I just keep on exercising the rams and expect any air in the system to eventually come out ?
2 Should I go around all the pipe ends and bleed them or check for Oil - Air ?
3 Are there any exercising tests I can do that may point at dodgy pump or controller or something?

Sorry to be a bit long winded (as per) but thought it best to layout what i've done first. :bow:
Hope some of you are still awake :lol:

Best wishes to all for 2018 :thumbup:

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Re: Hitachi EX27u Low Pressure ?

Post #2 by le.maisonniau » Mon Jan 15, 2018 10:25 pm

Hi Guys, since first posting, I seem to have 'fixed' the dozer blade issue :thumbup: after lots of testing etc, I noticed I was having to put a lot of pressure on the lever to push it down, so I stripped off the covering panel and found the lever was fouling its housing, there was plenty of adjustment, so I adjusted it (shortened it) and 'voila' it works a treat now, up and down no probs, lifts the m/c up and down effortlessly.

However, I still have the problem with the Boom :wtf: , i.e. If the dozer blade is down, there is little or no pressure to lift the m/c by pushing the boom ram down, BUT, in this postion if I turn the bucket - the bucket ram will lift up the m/c :dizzy: - I did replace the boom ram supply hoses :roll: and did check for oil - but will revisit the pipes and check again -

If anyone has/had a similar issue, I would be interested in testing procedures and solution :bow:

The problem as I see it now; with the Dozer blade down, there is no pressure to lift the m/c by pushing down with the boom.
As soon as I get chance I intend to take the m/c outside and see what happens if I try to lift a full 5' scoop up with the blade down, I guess I should get a similar lack of pressure :think: ?

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Re: Hitachi EX27u Low Pressure ?

Post #3 by Jeremy Rowland » Tue Jan 16, 2018 8:27 am

John it's good to hear that you are making progress :thumbup: sometimes issues turn out to have an easy fix at other times they don't; I only have a base knowledge of hydraulics so sadly I cannot be of much help to you with the boom issue, all I would suggest is if there is anybody you know that could check all of the hydraulic pressures for you it may point you in the right direction.


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Re: Hitachi EX27u Low Pressure ?

Post #4 by FOWLER MAN » Tue Jan 16, 2018 3:14 pm

Hi John,
I'm afraid I don't know the Hitachi EX27 but I do know hydraulics. Jeremy is right to suggest that a pressure check is the way to go.

If everything else but the boom are working OK that eliminates a pump problem. If the boom is lacking power both up and down that points to ram seals but if that was the problem you would probably expect the boom to creep.
If the boom lacks power in one direction only that points to a service line relief valve ,(SLRV), fault. ( I think Hitachi call them Overload Valves ). You would need a pressure gauge to check or set up the valves.

As the main line relief valve is set to a lower pressure than the SLRV it is usually necessary to increase the pressure there above the SLRV
pressure in order to set the SLRV and then reduce it to its normal setting afterwards.

As you have found with your blade it's always worth checking that control linkages move the spools to the end of their travel. On a servo controlled machine that can be down to low servo pressure.
I know this is all a bit vague, hope it helps.

Good luck.

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