Re: Hitachi EX27u Low Pressure ?
Posted: 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. 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.
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.
I haven't seen how your machine performs, but you may well be worrying about nothing.
The pressure test will give you the answer.
Fred
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. 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.
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.
I haven't seen how your machine performs, but you may well be worrying about nothing.
The pressure test will give you the answer.
Fred