CAT 301.6C jerky boom cylinder movement

[v8druid]

The he breather is metered, the leak is not! If it is a vacuum or pressure system, with a leaking gasket or seal, it will be both.

Mick

Tell me more Mick?
How is the breather metered?
I've often wondered why/how the tank's pressurised even with a breather fitted on my 'Drema?
Is there a pressure limiter/blow off in the breather or cap?
That being the case, I can see exactly where you're coming from, with any leak to atmosphere - it would affect the metering system and any required pressure build up, in the tank, to aid feed to the pumps ( and possibly cause/result in cavitation )

Every day's a a school day

[Mick-the-fitter]

Tell me more Mick?
How is the breather metered?
I've often wondered why/how the tank's pressurised even with a breather fitted on my 'Drema?
Is there a pressure limiter/blow off in the breather or cap?
That being the case, I can see exactly where you're coming from, with any leak to atmosphere - it would affect the metering system and any required pressure build up, in the tank, to aid feed to the pumps ( and possibly cause/result in cavitation )

Every day's a a school day

The example I will use is, a JS 130, the breather system uses a filter on top of the hydraulic tank and a one way valve, therefore you are able to unload back pressure by pressing the valve off its seat, when the machine has been run there remains a small pressure within the tank and subsequent hydraulic systems, so I guess the pump case pressure will at that point be equal to the small tank pressure!

The valve will be set against a spring of probably 1bar (guess)!

i would think that by the difference in temperature of working oil there would be a change in pressure, and if the system is sealed then low pressure supply/versus high pressure delivery oil would create a system differential oil pressure.

if then there was a tank seal breech then foaming and cavitation would be possible, even more so in a smaller tank, with less head room!

Mick

[v8druid]

The example I will use is, a JS 130, the breather system uses a filter on top of the hydraulic tank and a one way valve, therefore you are able to unload back pressure by pressing the valve off its seat, when the machine has been run there remains a small pressure within the tank and subsequent hydraulic systems, so I guess the pump case pressure will at that point be equal to the small tank pressure!

The valve will be set against a spring of probably 1bar (guess)!

i would think that by the difference in temperature of working oil there would be a change in pressure, and if the system is sealed then low pressure supply/versus high pressure delivery oil would create a system differential oil pressure.

if then there was a tank seal breech then foaming and cavitation would be possible, even more so in a smaller tank, with less head room!

Mick

Cheers Mick,
can see exactly where you're coming from with the (possible) seal issue now - makes a lot of sense, now it's mentioned and explained!
Presumably a little tank pressure also helps reduce the risk of foaming too?

[RedQueen]

Hi guys. Here I am reporting back.

Unfortunately I still haven't been able to measure the pilot pressure and flow because I am still waiting for the measuring kit that a friend has promised to lend me. But I did some tests and I was using the machine heavily over the weekend so I have some observations to share.

First I checked and yes if I move the tracks and at the same time move the boom cylinder the tracks slow down considerably. So obviously the same pump is powering both. Secondly I observed something that I can only describe as a light mist of hydraulic oil deposited on the hydraulic tank around the tank cover. I cleaned and degreased the tank in that so it was clean as a whistle so that greasy oil mist was a new thing. I checked screws that fix the metallic tank cover to the plastic hydraulic tank body ad two of the screws were a little loose so I tightened everything. The mist is gone so maybe there was also some air leaking as Mick suggested.

Unfortunately the problems persist. But as I was very attentive when I was using the machine one thing came to mind. When I move the boom cylinder I actually move quite some mass in relation to the excavator (it is only 1.6 ton) so the machine usually wobbles a little (swings back and forth). The direction is same as the direction on the right hand joystick control (forward - boom cylinder up, backwards - boom cylinder down). Do you think it is possible that the jerkiness comes from the fact that I unconsciously also move my hand slightly back and forth as the machine swings and that the hydraulic valve on the control is so sensitive that it is enough to cause the cylinder to jerk in motion? Is there any type of malfunction that would cause the controls to become too sensitive or is there any adjustment possible?
The exact same cause can be attributed to the jerky tracks movement when I want to go half speed. I can move smoothly either very slow (so slow that there is no wobbling of the machine) or at top speed (levers to the max). At any intermediate position the jerking appears...

Any thought welcome while I wait for measuring kit...

Regards, RedQueen

[Muz]

Well .. it could be a combination of things ofcourse .. One tonners are certainly notoriously jumpy .. and block archictecture in some machines is poor compared to others, meaning stroking the dipper in whilst gaining boom lift at the same time is not good .. you have to have experience of jumping on lots of diggers to really see the difference ... what made you buy the CAT ?

[RedQueen]

Well .. it could be a combination of things ofcourse .. One tonners are certainly notoriously jumpy .. and block archictecture in some machines is poor compared to others, meaning stroking the dipper in whilst gaining boom lift at the same time is not good .. you have to have experience of jumping on lots of diggers to really see the difference ... what made you buy the CAT ?

You're right. Well as soon I get the kit I will do the measurements that's least I can do do maybe learn something new.
Why CAT? Of course I am no expert in this matters although I want to learn as mush as possible. To be honest my brother got it because it was a collateral for a loan he gave to someone. Since he lives in an apartment in the city he had no idea what to do with it and it was siting in some depo for almost a year. I mean he really didn't even try to sell it all this time! He was always more on the light side of life I guess...
Then one day I complained over the services of some contractor that did some work around my house and he offered it to me for free. So I became a proud owner of small CAT (miew).
I use it every weekend (weather permitting) and apart from this issue discussed in this thread I am absolutely fine with it. Engine works like clockwork, power is there, almost no cylinder drift, nothing leaks and also no visible damage on the machine. So when I solve also this it will be totally OK.

Cheers!

[v8druid]

You're right. Well as soon I get the kit I will do the measurements that's least I can do do maybe learn something new.
Why CAT? Of course I am no expert in this matters although I want to learn as mush as possible. To be honest my brother got it because it was a collateral for a loan he gave to someone. Since he lives in an apartment in the city he had no idea what to do with it and it was siting in some depo for almost a year. I mean he really didn't even try to sell it all this time! He was always more on the light side of life I guess...
Then one day I complained over the services of some contractor that did some work around my house and he offered it to me for free. So I became a proud owner of small CAT (miew).
I use it every weekend (weather permitting) and apart from this issue discussed in this thread I am absolutely fine with it. Engine works like clockwork, power is there, almost no cylinder drift, nothing leaks and also no visible damage on the machine. So when I solve also this it will be totally OK.

Cheers!

My little Manor walking m/c is exactly the same with a very simple valve block arrangement. It can be multi spooled with great care and it is possible to grade with it, if you're careful (and have been on it an hour or two first), but it's no mean feat to get more than one function out of it at a time, which can be a PITA

All that said, it beats a shovel any day and has moved some serious quantities of dirt in the 20 odd years I've had it!!