Supermajor hydraulics.

[csvper]

After enduring bobbing lift arms for too long I have the lift assembly on the bench.
After rigging up an air line to the inlet hole I have worked the piston with air.
When filled with air lifting the arms with a bar the piston can be retracted reasonably easily with audible air escaping from the rear of the control valve plus visible bubbling from between the control valve and it's bush when light oil spayed on.

Would it be possible to assume this May be the culprit or is air an unreliable test?
Help in this diagnosis would be very much appreciated.

[Brian]

Air is not a good guide to a leak you really need to see it under pressure with oil. We used to have an old axle housing with the sides cut away, a hand operated hydraulic pump and two socking great weights to go on the lift arms. I know that is not possible in your case so you will have to do a visual inspection of the valve. Then you lightly oil the valve and it should drop through the bush under its own weight. If it drops through easily then it is worn and will leak.

Valves and bushes are colour coded to get the correct fit but be careful if you buy one of the after market ones. A valve that is a good fit in the bush may be too tight when the bush is pressed into the ram cylinder. We had all the colours in stock and many times had to change for a smaller valve after fitting the bush. The above test is how it should be.

If the valve is a firm/tight fit it has to be polished to fit with either Jewellers Rouge or Brasso metal polish. That takes some time. BTDTEP.

[csvper]

Thank you for your help Brian I will check the valve fit in the bush.
I have also found there to be no return/exhaust oil filter in the sump and removal of the pipe has shown up that the back pressure valve is incomplete the inside of it is gone.
I know it's there for a reason but how critical is its role?

[Brian]

Very critical, the valve maintains a back pressure of around 11psi in the circuit. This pressure is to work the unload valve. Without it you could suffer from the lift locking in the raised position.

[csvper]

Thank you for the info on the back pressure valve.
I have not had locking occur before but will source and fit one.

I have also found that the control valve will drop through its bush quite quickly resulting in a tap when it reaches the bottom.
I presume this is less than satisfactory...

[Brian]

If it falls through that easily then you have a problem. Something to try, check the paint colour on the shank of the valve and see if you can get the next size up. It will only be a couple of microns but it will make a difference. Agriline list the valves for the Dexta but cannot find anything for a Super Major in their catalogue. They have muddled things up for 2016 though, very poor after their 2015 version

[csvper]

After mulling over Brian's advise on control valve and bush fitting I took the lazy/more expensive option and fitted a new lift cylinder.
Finally hitched the plough on today and guess what.......
Still jumps up and down like it flaming well did before

Super major hydraulics,what a pain in the ass.
Process of elimination leaves the check valve I suppose.

[csvper]

Right then,removed check valve seems ok.

Pulled out check valve seat with special tool(bolt with correct thread ,weld on thread socket washer nut)
Ball and valve seat fit look ok.....until shine a small torch up from rear and bingo can see the light!!

Ball is ok the seat has a 30 degree blemish which shows with the aid of a torch but doesn't show so easily to the naked eye.

Hope this is of some help to others as this has now cured the problem..

[AdrianNPMajor]

Well done. Great piece of detective work.

Best, Adrian.

[csvper]

Really is good to have the tractor keep the plough up with ZERO corrections per minute.
Bit of a change from 30 or more..