Hitachi EX27u Low Pressure ?

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Re: Hitachi EX27u Low Pressure ?

Post #11 by FOWLER MAN » Tue Jan 23, 2018 10:45 pm

Hello again John,
I'm pretty confident that the machine should have cleared the air from the system by now.

If I may I'd like to make a few observations. :think: Firstly I don't think you should expect the machine to lift itself effortlessly with the blade on the ground behind as it will then be attempting to lift the whole weight of the machine whilst with the blade off the floor you are virtually only rocking it on its tracks.

The boom ram is mounted to give maximum power to lift the arm ,not to exert maximum downward pressure.
The power at the ram is in direct proportion to the piston area and when you lift the boom it utilises the whole of the piston area to produce maximum power.
On the downward stroke the cross-sectional area of the of the rod must be deducted from the area of the piston face reducing the power proportionately. :geek:
Also, because the same volume of oil will be pumped into both ends of the ram and it will take less oil to fill the rod end, the ram will travel faster when closing. This has the effect of gearing up the system and also reducing power on the downward stroke. :ugeek:
I haven't seen how your machine performs, but you may well be worrying about nothing. :roll:
The pressure test will give you the answer. :thumbup:

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Re: Hitachi EX27u Low Pressure ?

Post #12 by le.maisonniau » Sat Jan 27, 2018 11:52 am

Hi Fred,
Sorry I am just getting back to you, I didn't spot my topic had gone into 2 pages :roll:
:bow: You are absolutely correct. :bow:
My Mate came over on Thurs and we (he mainly) took off the dipper ram and replaced a leaky seal [1 hour] There is now NOT ONE drop leaking anywhere on the m/c- well impressed :claphands:
He forgot his pressure guage but we exercised the m/c and I walked him through my concerns over the boom not raising up the m/c.
He told me exactly what you have said and that the m/c wouldnt/couldnt lift up as I was expecting.
The m/c is well up to spec pressure wise as well, even without testing the pressure, judging by how easy and quickly I can lift the m/c up on the blade etc. how quickly and smoothly all other rams work.
I understand now your physics on the rams etc. and as you point out the dozer Ram has a much larger cross sectional area and shorter stroke, which is why it works as you describe.
Many thanks for you informative reply and again a confidence boost.
I just need to wait for the rain to stop so I can get outside and give the new bearings on the tracks a test, then it is just tidying up the body panels, adding a couple of whizzy LED worklights (Just got some off Amazon 16LED in a 4x4 matrix 48watt 6500k for 8euro each :thumbup: Hope they last :lol: ) and then get the m/c up my woods for some serious work. :thumbup:
When you come to a fork in the road - take it :dizzy:

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