View Full Version : Another 'It Follwed me Home' and a hydraulics question

10-16-2007, 05:45 PM
Not entirely OT, there's bound to be some machining involved somewhere along the line.....

I mentioned this in another thread ('Dog House'), it's arrived home now:-


In the middle of Harecastle Tunnel, 1.75 miles long, took us 1.5 hours to get through:-


Passing down 'Cheshire Locks', we had to pass 35 locks altogether (and about 35 miles, some of them very slow when the water was a bit shallow!)


Arriving 'back at base' 3 days after setting off:-


To the hydraulics question:-

There is an issue with the hydraulics (JCB Back-actor and the stabilising 'spud legs') in that they all work fine, but will steadily drop under their own weight - sufficient to be a real nuisance.
I've no experience of this sort of gear, the magic word 'spool valves' has been mentioned, and that they sometimes develop cracks. Any comment from someone who knows? The whole thing was 'rebuilt' 8 years ago, including a new back-actor, and hasn't exactly been worked hard since then.


10-16-2007, 06:01 PM
Interesting Machine. Here in the desert that would be hard to use:D Hyraulics will leak down if the seals in the spool valves or the cylinders become worn or cracked. It is a common thing to reseal the controls and cylinders of our tractors. It is not hard just takes time and some big tool for the big stuff.


10-16-2007, 09:55 PM
Zukizzy already mentioned two common things with the cylinders and the valve body. Something that I found out was that cyclinder walls will become corroded by water sitting in them (yes, along with the oil). Makes for nice little pits that allow oil past the piston & seal rings. Not so much a problem on the rod, as it is hard chromed....

This is particularly a problem on hydrauic systems that sit idle for long periods of time (so the oil doesn't get warm and evaporate the condensation) and that exist in moist environments.

I have a 1970's MF202 backhoe (used intermittantly) and live near Vancouver
(may as well be under water most of the year...).

The cure in serious cases is to replace the cylinder barrel (nice machining & welding job) or try replacing the piston seals.

Good luck with your dredge.

10-17-2007, 12:39 AM
My money is on the seals in the spool valves. Best possibilites are seals being hard.This is easy to identify,just remove one set and see if they are nice,round and pliable,if not they will be hard,brittle and nearly square in crossection.Your classic hard,dry rotted o-ring.

Other possibility is when the system was rebuilt,they didn't take time to debur the fluid ports,as a result as the new piston seals passed over those ports the sharp edges shaved material off the seals making a slow bypass leak.

10-17-2007, 04:31 AM
Thanks guys, first job is to find the spool valves! Probably under the decking somewhere, this thing has what I think are called pilot valves, joysticks on either side of the seat which AIUI operate a small valve which in turn works the main valve.

The label on the oil tank specifies Biodegradable hydraulic oil, which I believe is Veggie based, this will be a legal requirement here in a few years for this sort of application. I do know that the maintenance guys at British Waterways have used ordinary ISO 32 oil recently, I wonder whether the seals need to be different materials for the two oils?


Weston Bye
10-17-2007, 06:27 AM
During rebuild you might want to consider installing pilot operated check valves in lines to the spud legs and the boom of the backhoe. The checks, using balls or poppets, seal better than spool valves. A separate pilot line connected to the opposite port of the cylinder opens the check to allow reverse flow when you actually want the cylinder to move.