Hydraulic steering/ tipping on a Thwaites articulated dumper

[milesclinch]

Hi,
I am a new member trying to sort out a Thwaites 9000 Mark III, the serial number is 1 74135. It has a 3 cylinder Petter but the name plate is Lister Petter so probably made when they merged. The engine number is 3600083P6003A00.
If the model does not match the numbers please let me know.
Problems exist as always on old machines. The tipping spool valve is a Cessna. I cannot find any info on this via the web. the number cast in the body is 9D 49 TC 3000 024 KAC. This was replaced by another scrap yard one and I can say the tipping ram seems to work OK. This was after changing the hydraulic oil (including some gear type oil) and renewing the metal gauze inlet filter in the tank and the return filter. An orbital steering motor at the base of the steering column has seen very little use (if any). Naturally with the tipper working I thought everything would be fine. NO WAY. Sometimes the dumper would swivel then just straighten up and sometimes I could not turn the wheel one way but ok the opposite direction. This leads me to think there is a blockage in the orbital steering motor. How do I check this out? Recently I noted on these webpages references to pipes degrading internally and a means of assessing this problem would be welcome.
The spool valve has a relief valve in it and I wonder if this is blowing. Some net pages seem to say always change the relief valve when changing the oil. But that is catch 22 with CESSNA having stopped production. Any suggestions?
Does anyone know of a manuals on this machine?
I think this is a good introduction of me and my problems. Maybe too many. However any help or suggestions are welcome.
Mileclinch

[Sabs78]

Miles,
There is certainly no need to replace the releif valve every time you do an oil change and that would certainly be an over kill, the problem with the orbital valve definatley sounds contamination related and will more than likely require the orbital valve to be removed and serviced.
The most common cause of contamination in the orbital valve is the internal seals on the steering ram breaking up so if your looking for the cause thats where i'd start, as for the orbital valve itself theres plaenty of hydraulic shops you can send it to for recon and obviously spares will still be available for the machine. The manuals for the machine can usally be sent from Thwaites via e-mail if you contact their service department.

[milesclinch]

Andy,
Thanks for reply. Once I get the starter motor re-installed and engine going again it was my intention to see if the steering ram pipes delivered any oil. Your comment is certainly the likely course of action. Before clearing up some of the problems I thought there must be a 'travelling blockage'. Sometimes it steered easily sometimes it tipped easily. Only one at a time and revving the engine up a bit. Now filters are clean and hydraulic oil all the correct grade it should operate perfectly!!! only the steering to do!!
Miles

[milesclinch]

Further to my original query can anyone tell me the hydraulic system pressure?

[Holger]

Nobody able to help Patrick?

[milesclinch]

Further to my original query I can update the hydraulic pressure. A gauge on the delivery into the steering motor registered 1000 psi on tickover rising to 1500 psi when the engine revs were increased. Naturally the steering wheel had to be turned to get the reading. The same reading in each direction.
If anyone has a comments on these pressures I would be glad to read them.

[Sabs78]

Miles,

From the description of the steering fault you are experiencing the seals in the steering ram are more than likely shot to pieces, you can probably save yourself a lot of time by removing the ram and stripping it. It the ram seals have failed then you can certainly gurantee that they have got intot he steering valve which is why its locking up. Also the system pressure for this machine should be 2000psi.

[milesclinch]

Thanks for your reply Andy.
Currently trying to remove the pin holding the ram near the engine. Some freeing agent or heat maybe required. The front pin under the bucket is easy to remove. My investigations show there could be problems with the ram. The orbital motor is being servised - I do not know what they found as yet.

[milesclinch]

An update.
The orbital steering motor was found to be in good order and the problem was the steering ram. From my original description it was difficult to think it was the cause. When it was dismantled it appeared the piston on the end of the doulble acting ram was broken and had become detached from the ram. This accounted for the partial operation and leakage etc. Anyway all is well now with the steering and tipping.
The CESSNA Valve block had a pressure relief valve in it. I wondered if it was all present in my original description. I also notice another member has problems and presented a photo of the valve block with part of the casting broken off. Does anyone know of a source for a drawing of the valve or of the valve block of which it is part. I have mentioned the pressures I found and they are nearly 1000 pounds below a 2000 lbs operating pressure. Any help will be appreciated.
Pat

[Julian]

I have mentioned the pressures I found and they are nearly 1000 pounds below a 2000 lbs operating pressure. Any help will be appreciated.
Pat

I've got no real idea of the operation of this particular hydraulic system, but what I can say is the the 'operating pressure' would probably be better refered to as the system relief pressure. This pressure will only be observed only when the operating ram is stalled, either by it reaching the end of its travel or the machine stuck in a deep rut perhaps.

Julian.