Relieving hydraulic pressure when changing boom hoses

[Welder Dave]

I need to replace a boom cylinder hose on my backhoe. I'm going to stretch the stick out all the way and put it down a slight slope so the boom cylinder is angled downwards at the swing tower. I figure it will lessen how much oil spills out. Would lowering the boom with the machine off result in less oil in the cylinder than if I lowered it with the machine hydraulics? I think it would but not sure. The cylinder holds a lot of oil that I don't want sprayed all over.

 

[ExcavatorPartsVincent]

I would assume the hose and both sides of the cylinder still have trapped pressure, even with the boom down. Lowering with the engine off after cycling the controls can bleed pilot/valve pressure, but it will not necessarily drain the cylinder. If the cylinder can move or is holding any load, crib or support it first.
Before cracking the line, I would put the attachment down and blocked, shut the engine off, cycle the controls through all positions a few times, relieve tank pressure if it is a pressurized reservoir, then wrap the fitting with a rag/cardboard shield and loosen it very slowly. Keep hands and face out of the spray path because hydraulic injection injuries are no joke. Cap or plug the open hose and port as soon as it is loose.
The slope may reduce the mess a little, but I would plan on catching oil and not count on the angle to prevent a spray. If the service manual has a pressure relief procedure for that boom circuit, follow that first.

 

[Welder Dave]

There's no pilot pressure. It's simple open center hydraulics. Of course the boom will be on the ground and all controls cycled to relief any pressure. I'm wondering if lowering the boom by cycling the valve with the engine off will result in less oil in the cylinder? I'm thinking it will push oil out holding the boom up but won't introduce oil to lower the boom. I know it will be messy but I'm hoping to make it less messy.

 

[franklin2]

All cylinders will stay filled on both sides at all times. It's not like you are introducing air or have a vacuum on the cylinder by moving it a certain way, it would not work correctly if it did that. The best you can hope for is to mechanically relax the boom on the ground, and then move the valving with the engine off. That should relieve the pressure but will not make the oil vacate the cylinder or the hoses.

 

[Deere500a]

Engine off pressure bleed off said above it should only be oil in the hose deal with minor mess pig mat under the fittings keep boom clean.

 

[Welder Dave]

Well I guess I'll find out.

 

[Welder Dave]

Update: I think the damaged hose was for the stick cylinder. If it was for extending could explain why it hasn't blown. Extending the stick isn't normally used for heavy loads.
Lifted the boom to full height with the stick all the way out as well. Shut the machine off and slowly lowered the boom to the ground. The boom cylinder was on slight downward slope out the shop door. I built up the shop floor so there's a slight ramp up to it. Had to take off a stick hose above the one I'm replacing so I could get a wrench on it. Was surprised that very little oil came out. Great! Loosened the hose I'm replacing and some oil was leaking out but got the fitting off and not much more oil came out. I was surprised but glad that only a minimal amount of oil leaked out. With the ends capped there was still a little dripping so I'll see if much oil accumulates in the drain pan I put underneath. I don't think there will be but stranger things have happened.

Thankfully the hose on the control valve was on the top and I didn't need to remove any other others to be able to get a wrench on it. It was difficult to turn the nut with my fingers though because there is a steel line that goes across the fitting. Hopefully I won't have trouble getting the new hose started. I'll see if the hyd. shop has extra length bulkhead fittings to mount on the hose support. Cat doesn't make the reusable fittings that clamp in the hose support anymore which sucks.

 

[Welder Dave]

Last pic. where he hose connects in the boom. I forgot there were bulkhead fittings and the hoses weren't one piece all the way up the boom. I was having a heart attack thinking I'd have to take the boom cylinder out! It weeps a little but not bad enough to reseal yet. If it gets worse I'm hoping to just pull the rod out and leave the barrel in place. For now I'll just be happy to get the damaged hose replaced before it blows up.

 

[Welder Dave]

I was confused. It can't be for the stick cylinder because it's controlled by the left joystick. So it must be for the boom cylinder.

 

[Deere500a]

Little can tell looks like a International hoe. Right on

 

[Welder Dave]

It's Cat quick attach backhoe for a D3B, 931B, D3C, 931C and also fits on some D4's and other track loaders like 935.

 

[Deere500a]

Made it Japan? Swing motor is odd how new machine is mostly by 70s motors disappeared for swing cylinders

 

[Welder Dave]

Yes, made in Japan. It's an 86 but I'm pretty sure Cat still offered it into the 90's using the rotary swing cylinder. I had to have the shaft built up because it leaked out the bottom. Apparently that was a common problem with rotary swing motors. The vane seals were still good and the other seals were still available. I'd guess they were used on other equipment. I'm not sure if the swing motor is made by Cat or is possibly made by Cessna because there are no markings or numbers on it anywhere. Maybe Cat made it under license or copied a Cessna?? It looks very similar to a Massey Ferguson rotary swing cylinder which was made by Cessna. It seems odd to me that if it's made by Cat it doesn't say Cat or have any part numbers on it. It's kind of like it's a generic swing motor but that doesn't make sense. Cat also had a side shift hoe that I think used the same swing motor. That's probably why it was also used on the std. hoe. I even saw a machine with a Cat quick attach hoe with extend-a-hoe which has to be incredibly rare.

 

[Deere500a]

Deere's lineup of hoes 93,9300,9400 & 95 are swing motors. I wouldn't be surprised the motor is outsource

 

[Welder Dave]

The JD swing motors look different from Cessna swing motors on Massey backhoes or Cat swing motors. I think Allis Chalmers used the Cessna swing motors too.

As far as hydraulic fluid I hardly lost any, maybe 1/2 a litre at the most which is good. Usually I'll lose 4 or more litres when changing a hose. Apparently the original hoses were 4 wire. I just got 2 wire so it was easier to bend. System pressure is only 2500 PSI. The 5/8" hose is rated for 4250 PSI. I had them put some protective sleeve on the hose.