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Thread: Baffling Hydraulic Problem

  1. #1
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    Baffling Hydraulic Problem

    So, we have a cabless Leyland 270 with a Horndraulic loader that we use in a couple of old buildings that are too low for the other tractors.
    This weekend we decided to swap the loader for a, slightly less ancient, Mil loader that was recently decommissioned from a 262, because it has a much better reach for loading into the trailer.
    When we went to try it, the crowd rams wouldn't retract Whichever way you moved the lever, they only extended. i.e Push lever forward - ram extends, pull lever back - ram still extends.
    I should say, at this point, we never touched the hydraulics on the tractor. We left the spool block from the old loader on the tractor and just connected the pipes to the Mil loader.
    Clutching at straws, we swapped the pipes over and lo and behold, it worked fine. Only the lever works the wrong way round now. So we swapped the pipes back again and the same thing happened again, the ram would only extend. Swapped them again and it worked again. That's how I was using it today but it's a PIA with the lever working back to front.

    Hopefully you guys can understand the post
    Any ideas?

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    Senior Member Footsfitter's Avatar
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    Re: Baffling Hydraulic Problem

    Quote Originally Posted by MC130 View Post
    So, we have a cabless Leyland 270 with a Horndraulic loader that we use in a couple of old buildings that are too low for the other tractors.
    This weekend we decided to swap the loader for a, slightly less ancient, Mil loader that was recently decommissioned from a 262, because it has a much better reach for loading into the trailer.
    When we went to try it, the crowd rams wouldn't retract Whichever way you moved the lever, they only extended. i.e Push lever forward - ram extends, pull lever back - ram still extends.
    I should say, at this point, we never touched the hydraulics on the tractor. We left the spool block from the old loader on the tractor and just connected the pipes to the Mil loader.
    Clutching at straws, we swapped the pipes over and lo and behold, it worked fine. Only the lever works the wrong way round now. So we swapped the pipes back again and the same thing happened again, the ram would only extend. Swapped them again and it worked again. That's how I was using it today but it's a PIA with the lever working back to front.

    Hopefully you guys can understand the post
    Any ideas?

    The surface area on the rod side of the piston that is trying to pull the ram in is the same OD as the other side of the piston-but its less the diameter of the rod, so there is an imbalance in the surface areas - apply the same pressure to both sides and the ram will open out on its own it has no choice.

    Working on that theory it sounds like there is a big back pressure in the return from the spool block to the tractor? or there is damage to the crowd spool? or there is something "weird" about it- ie a motor spool? (oil flow one way & dump to tank in the other to allow a motor to slow to a stop)

    Strange that the former crowd rams worked but not seeing the actual items in the flesh makes it a bit of guesswork!
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    Senior Member T P's Avatar
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    Re: Baffling Hydraulic Problem

    Single acting spool splice? Did the Horndraulic definitely lift the tractor front wheels off the ground? Will the new loader lift the front wheels off the ground? Very interesting puzzle but there will be an answer. I'm thinking the former loader was single acting with drains from the other end of the ram connected to the return circuit. Most old single acting spool blocks used to have a plug for the other unused line that might have simply been a drain line. Some detailed photos would help as I haven't seen either loader anywhere.

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    Re: Baffling Hydraulic Problem

    That would be unusual to have the crowd rams on a single acting service even going back years.

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    Senior Member T P's Avatar
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    Re: Baffling Hydraulic Problem

    Quote Originally Posted by essexpete View Post
    That would be unusual to have the crowd rams on a single acting service even going back years.
    Very true but then we don't know that the original loader was piped up right even though it worked, there were quite a few old single acting boom lifting rams that had drains the other end in days of old. I was wondering had the spools been swopped to suit someone and that worked fine on the first loader but not the second, perhaps the latter one has long thin rams that have very little power to retract and there is enough low pressure backpressure on the other side to overcome them, this might not have been a problem on a loader with short fat rams. Blue Leylands had a "pressure beyond" feature that permitted the one pump to drive the spools and three point lift in series. I am wondering if the pipes are on it wrong for years and it's only rearing it's head now? Really it's all total speculation without at least pictures. Is it using the tractors own spool valves or another set fed from them-too many unknowns. Gauge in the return line to check there isn't a load of backpressure would be a good start. I don't have a blue Leyland Manual but the schematic for the yellow 502 is similar (attached) I saw a few malfunctioning loaders etc years ago because many of the pipes have the same ends and are easy mixed up. Steering wheel attendants swopping the 3/8 bsp pipes on number 5 used to a classic expensive mistake resulting in splitting the hydraulic pump in two when a ram hit the end stop as there was no longer any relief valve in the circuit! One other thought is there a QR fitting somewhere that is snapping shut and stopping the flow in one direction, any suspicions pipe direct temporary without QR to eliminate.


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    Re: Baffling Hydraulic Problem

    Thanks for the replies

    Sorry I don't have a camera at the moment. My phone got broken recently and I'm muddling through with an old one till Jan, when I'm due for an upgrade anyway.
    I've found a couple of pictures on google, though.

    The Horndraulic looks like this https://www.i-bidder.com/en-gb/aucti...4-a48800f40857
    And the MIL looks like this http://picclick.co.uk/Leyland-272-2W...l#&gid=1&pid=4

    FF makes an interesting point about backpressure. When I think about it, the engine does labour slightly when you tip the bucket. Not what you'd expect when the bucket is actually pulling on the rams

    TP - Yes, dodgy QR couplings was the first thing we thought of, so we changed them first. Your point about short fat rams against long thin ones is a good one as that is indeed the case. However, what I think is more important (and it just dawned on me today ) is that the rams work the opposite way on the two loaders. So the chances are, the 270's always been like this but because the rams worked the opposite way, the lever was working the right way round (if that makes sense?).

    I think I've got another double spool block somewhere, if I can find it, to try. If that doesn't help then I'll see if I can borrow a gauge somewhere.
    I think the spools from this MIL loader (which originally came on a s/h 255) went away on a 282 (the 262 didn't use them, it has extra factory fitted auxiliary spools under the back of the cab and the loader was plumbed into them) after we swapped loaders with the one that was originally on the 262 in order to keep the best one.

    Might not get time to get back to it before Xmas, but I'll let you know what happens, thanks again

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    Senior Member ACE's Avatar
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    Re: Baffling Hydraulic Problem

    I have not read through ever word here but I would say the ram seals are gone on the pistons so the rams have turned in to single acting.

    Edit reading through its either ram seals like I said or more likely you have used a single acting spool to work the tilt/crowd.

    Either way shouldn't be too difficult to figure out.

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    Re: Baffling Hydraulic Problem

    Quote Originally Posted by ACE View Post
    I have not read through ever word here but I would say the ram seals are gone on the pistons so the rams have turned in to single acting.

    Edit reading through its either ram seals like I said or more likely you have used a single acting spool to work the tilt/crowd.

    Either way shouldn't be too difficult to figure out.
    No, the ram seals are fine and the spool is definitely double acting. I haven't had a chance to get back to it but I was speaking to a local engineer and he thought some kind of internal fault with the spool, which was one of FF's suggestions also, so I'm leaning toward that.

    The rams aren't actually that old. We had to get a pair made for that loader about 4 or 5 years ago. The spool, however, was probably the one Noah used to lift the ramp on the Ark

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    Re: Baffling Hydraulic Problem

    Found the spare spool block today and swapped it with the one on the tractor. Everything working as it should now

    Thanks for all the replies

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