HIAB Legs stuck ...... why? & how do we fix

[ben lightfoot]

something you may well have tried is there any lever from the spool valve block that has to be depressed whilst holding the lever for the legs?

[Will Hinchliffe]

something you may well have tried is there any lever from the spool valve block that has to be depressed whilst holding the lever for the legs?

 

This could be the case but we have not got it to work yet.

 

The legs are piped directly from the pump. The spool valve block is then attached to this pipe with a T joint.

[combined tree services]

do you have one or two pipes to each ram ?

[treequip]

Your crane is a bit of an antique but from memory this is how they work, the valve you have pictured is a diverter valve, it should have three positions one will extend, one will retract and one will lock the leg out

 

Oil will be supplied to the diverter valve from one of the functions on the main valve chest, which in turn should not operate unless the diverters are both set to lock the legs out. (normally the middle position)

 

Try this sequence, run the pump and set one leg valve to the middle and one to either of the other positions. Now try the levers on the valve chest in sequence, one of them should make the leg extend or retract, if the leg is fully extended and you have set to extend nothing much will happen, set the leg valve to the other position and try again.

 

Andy

[PeteB]

There was some mention of a ball bearing and spring. This sounds like a "blow off" valve which is there as a safety. Too much pressure and the oil pushes the ball against the spring thus easing the pressure. If you have messed with the settings then you may have hosed it up wrong or increased the pressure that the oil will blow off at.

 

On my old truck that lever was a basic safety tap. Horizontal to work, down to cut off flow (I think anyway - it was many years ago!)

[Breezeblock]

is the rest of the functions on the hiab working properly stick a gauge on the valve block and check the pressures as most jack legs have pilot operated check valves so theyre might not be enough pressure to lift the check valve

[Will Hinchliffe]

Thanks for all your replies. Keep them coming.

 

We lifted the trailer to remove the pressure from the rams and have disconnected them from the trailer to take the valves apart again.

 

do you have one or two pipes to each ram ?

2 pipes

 

Your crane is a bit of an antique but from memory this is how they work, the valve you have pictured is a diverter valve, it should have three positions one will extend, one will retract and one will lock the leg out

 

Oil will be supplied to the diverter valve from one of the functions on the main valve chest, which in turn should not operate unless the diverters are both set to lock the legs out. (normally the middle position)

 

Try this sequence, run the pump and set one leg valve to the middle and one to either of the other positions. Now try the levers on the valve chest in sequence, one of them should make the leg extend or retract, if the leg is fully extended and you have set to extend nothing much will happen, set the leg valve to the other position and try again.

 

Andy

 

The diverter valves are piped straight to the the same pipe that supplies the main valve block for the crane. I think the diverter valve should work independently with out using the levers that control the crane.

 

There was some mention of a ball bearing and spring. This sounds like a "blow off" valve which is there as a safety. Too much pressure and the oil pushes the ball against the spring thus easing the pressure. If you have messed with the settings then you may have hosed it up wrong or increased the pressure that the oil will blow off at.

 

On my old truck that lever was a basic safety tap. Horizontal to work, down to cut off flow (I think anyway - it was many years ago!)

 

The diverter valve has four ball bearings in it. One is part of a one way valve that is on the pipe that supplies the pressure. The other 3 sit over the holes that the oil is to be diverted through. One hole leads to a galley that supplies the top of the ram, one to the bottom of the ram and one hole allows oil to flow back to the tank.

 

The lever operates by opening one or 2 valves at a time to either extend lower or lock the ram.

 

I think either the valves are opening out of sequence or one of the valves (the one that allows oil to flow back to the tank) is not being opened.

 

I have a photo of the lever, pistons valves and springs on my phone. I will try and borrow a card reader to get it on here.

 

I bet allot of you if you had it standing in front of you would be able to solve this very quickly.

 

Thanks again for every bodies input.

 

Breezeblock when I get a picture up of the insides of the diverter valve can you tell me if its a pilot operated check valve as I have no idea what one is. We dont have a manual for it so I have no idea what kind of pressure I should expect.

[Will Hinchliffe]

is the rest of the functions on the hiab working properly stick a gauge on the valve block and check the pressures as most jack legs have pilot operated check valves so theyre might not be enough pressure to lift the check valve

 

Just "pilot operated check valve" and got this:

The pilot operated checkvalve

 

Im thinking you may be right. We have just been running the pto on tick over

maybe there isn't enough pressure to open the valve.

[Will Hinchliffe]

CHAPTER 10: Directional Control Valves, part 1

 

This seems to have the answer in it somewhere Im sure

[Will Hinchliffe]

Im back thinking about it again and I have been reading up about pilot operated check valves. It seems some are pressure sensitive and some not. I found this picture of the valve on the legs. Does anyone know if this kind of valve would be pressure sensitive ?

 

Oil comes in the top pipe and out the one on the right.

 

The balls cover holes that oil can flop down to the top of the ram, the bottom and back to the tank.

 

the leaver moves the little pistons that push the balls.

Edited March 5, 2011 by Will Hinchliffe