Louisville LNT8000 tipper hoist won't come down

[Nick009]

I tipped out some sand today, after that my hoist wouldn't come back down. I checked for air on both the up and the down lines and they seem fine. (the hoses thrash around when disconnected) I think this is the diverter valve?



I was lucky to get some phone advice and I pulled the cap off and prised the piston towards me with a large screwdriver.



the hoist started coming down slowly so I put it all back together and tried the switch in the cab again. no luck. pulled the cap off again and bought it down all the way.

It seems that this has seized up, it goes up no problem but wouldn't come down.

two questions please, what could cause this and how can I fix it?

many thanks!

Nick

 

[51kw]

Do you have air to that side of the piston?

 

[mitch504]

Yeah, the air from the valve is the first thing to check, next is the air cylinder bore and o-rings.

 

[willie59]

Just be careful working on components with that dump bed raised.

 

[Steve Frazier]

I thought the same thing when I read this. Please be sure your dump body is securely blocked before working on the valve!!

 

[Nick009]

Yes there is air to both sides when the appropriate switch is pressed in the cab. What do I look for with the bore and o-rings? From what I can tell they look in reasonable condition.

And yes when I start working on it I will be putting a block in. thanks!!

 

[Steve Frazier]

I'm not familiar with this set up but it looks like the air pressure moves the hydraulic valve. On the air side, look for any nicks in the o-ring seal, which appears to be the red one. Also see that the bore is not scratched to where the air can pass the piston. The problem could be within the hydraulic portion. I can't see from your picture, but does the spool protrude from the valve body on the other end? If so, is it clean? If it's covered, remove the cover and see what you have. I had one cap fill itself with rust and seize the spool to where the control cables broke. If the hydraulic pressure is released, meaning you've actuated the valve in both directions with the body blocked and pump off, you should be able to move the spool fairly easily by hand. I'm betting this is where your problem is.

 

[willie59]

That looks like a crown seal. Odd application for that seal as it's typically used in oil applications. Seal should be smooth all the way around, and it has an o-ring loader under it. If it's deteriorated, the crown won't seal. But given you stated the bed will go up indicates the crown seal is good as that's a double acting valve servo. There has to be springs, either one on each side of the valve or both on one side that centers the spool. As Steve noted, make sure you can move the spool freely (aside from pressure from the centering springs).

If it moves back and forth with no binding, and once you've confirmed you have good air supply from that tubing, I'd be suspicions of the rod seal. There has to be some form of seal on the piston rod (see red arrow). If that seal were failed, you would simply leak air into the hyd section of the valve and not put air pressure against the piston.

 

[Nick009]

does the spool protrude from the valve body on the other end? If so, is it clean?

I'm not sure I'll have a look and take some more photos later.

I'd be suspicions of the rod seal. There has to be some form of seal on the piston rod (see red arrow). If that seal were failed, you would simply leak air into the hyd section of the valve and not put air pressure against the piston.

How do I get a look at the rod seal? its all pretty tight in there.



I should probably mention this again at this point. This is my first truck so I'm on a steep learning curve at the moment...

Thanks guys!

 

[willie59]

I can't really help you with specifics Nick009 as I've never worked on an air operated dump bed valve. I'm only saying, there has to be some form of seal for that chrome piston rod. If you've verified that you have good air pressure on that (inside) line, that piston seal is good, and that spool moves freely with not binding or tight spots (centering spring tension notwithstanding), then I'd suspect a failure of the seal for that piston rod.

 

[Steve Frazier]

When was the last time the dump worked properly?

 

[Nick009]

about 10 days ago was the last time I used it and it was fine.

I did haul a rather large load of sand with it yesterday, could that effect it?

 

[mitch504]

That air cylinder is a little different than the ones you usually see on Commercial Shearing dump pumps. Is that valve separate from the pump, or is it all in one housing?

I've never actually worked on an air cylinder on a separate valve. I agree w/ Willie ( ), Those packings look more like hydraulics than air cylinders. These air cylinders usually just use o-rings.

These control cylinders don't have centering springs, they use air pressure to choose raise, neutral or lower. These are basically converter kits that attach to the hyd. valve spool.

When I've had similar problems, if it wasn't something like a melted air line, the problem is usually in the hyd. valve, not the air cylinder.

To take the cyl apart further, you have to find how it attaches to the shaft of the valve. You may have to take the piston off the shaft so you can slide that round housing off.

Before I did that though, I would look at the other end of the shaft where it comes out of the other side of the hydraulic valve. There may be a piece that you can hook a cable to to pull the valve to neutral when the bed gets to the top. I have had to take this part off before.

If you post a couple more pics of this valve from other angles, I'm sure we can work this out. I have had similar problems many times before and they all turned out to be simple.