johnny5.9

Hi Guys. I figured enough guys around here are technical enough to perhaps help with my issue. I have an 08 12K dump trailer that I've had since almost new. Back in the day, it'd dump anything you could put in it. Even heavily overloaded it'd dump without much strain. I have noticed though, over the years the dumping power has reduced. The unit has a new motor, solenoid and batteries. So my question is. Does the fluid bypass circuit loose it's holding power over time? I'm assuming there must be some spring loaded valve that will divert fluid when you reach your max cylinder travel so you don't blow things apart. Can this be changed? Is it in both cylinders? Or in the main power unit. I don't know a ton about hydraulics. Maybe someone here does. Thanks guys.

roughstock

There is prob a bypass/relief valve in the pump. Could be weak or the pump is getting weak.
but Id check the cylinders. One may have gotten weak. I would disconnect one cylinder and plug the lines, then raise the bed with one cylinder and see if it bleeds down. Then do the same for the other. If it bleeds down, that cylinder is bad and needs resealed. Obviously, be careful when opening hydraulic lines and working under a raised dump body.
Hope this helps.

johnny5.9

That helps very much. I didn't think of doing that. Thanks! I'll try it and see what I get.

Busboy

Seals are very cheap and if the trailer has been used lots I would just pull both cylinders and install new seals, it doesn't take much wear on a seal to allow it to bypass. As roughstock says be careful working under a lifted dump trailer and always use the maintenance safety stop.

KATOOM

By all means NEVER climb under a raised bed without one or two things supporting it besides the ram. I've been around short haul dump trucking and thats a rule because when you have a ram or line blow that bed comes down like nothings holding it.

As for the lifting power, I'd call the hydraulic pump manufacture and ask them if there's something you should be looking for. A ram with weak seals will leak, not loose lifting power.

j_martin

Like he said. Pumps lose their goodie after awhile. If the relief valve is good, the pump is worn out.

Busboy

Not quite true, a ram with "weak" or worn piston seals will not leak externally but will bypass internally causing a reduction in lifting power and the piston to drop when hydraulic power is turned off, the piston seals for both cylinders would be less than $20. Actuators that are bypassing internally and have constant hydraulic pressure can become too hot to touch and can be heard squealing. I have a tilt cylinder apart on the bench at the moment it has around 250 hours on it and the piston seals are toast. It could be the pump also but the piston seals are so cheap to replace as a first step.

KATOOM

Good to know.....but I dont think I've ever had a ram go weak on me. Yes, bleed down is a leaky internal seal but the immense amount of pressure going on inside there means that if the ram isnt lifting then its usually a pump issue. But thats all I know.

pind

Ok, so what happens in the case of an internal seal leak.

Let's use 1000psi as a number. The cylinder will have 1000 psi applied to raise it, however, as the pressure increases, the slippage does as well. At this point, the cylinder will be seeing 1000psi on both sides of the piston. The side with the larger surface area will still win, but lifting power and speed will be greatly reduced. As well, if the cylinder is left loaded, with both ports capped, it will eventually return to the lowered position. This is again due to oil bybypassing the faulty internal seal.

j_martin

Just to clear things up a bit. A displacement cylinder can't bypass without leaking. A 2 way cylinder can. Often 2 way cylinders are used where a displacement cylinder will work as the shaft side of the cylinder is used for oil storage, allowing a smaller storage tank.

johnny5.9

To resurrect an old thread, I still haven't addressed the trailer. But it's going in tomorrow as it's costing me too much time and labour now. It's gotten worse. I talked to one hydraulics shop here that relunctantly ball parked me over the phone 500-800 per cylinder. Which seems like a ridiculous rip off to me. But I've never worked on them and I guess they can be a pain to get apart? I don't know. I've never worked on them and don't want to. I'm hoping the cylinders are fine and it's the pump or bypass valve. I really don't know what kind of life to expect from the cylinders but this is a dump trailer that gets dumped less than once a week during the summer and sits all winter. It's not like it's an excavator arm or something. So here's to hoping the cylinders are good. Do you guys have any other input? Thanks.

KATOOM

My money is on the pump.....

Busboy

I agree.. It could be the pump but I rebuilt that tilt actuator, the seals were $34 for 2 complete sets. It's very easy for a piston seal to roll over and cause an internal bypass. As modern dump trailers are power up power down they must be 2 way cylinders so it is possible for it to be a cylinder bypassing but around here you can buy brand new cylinders for around $300 so the quotes the OP got to rebuild the cylinders are ridiculous.

johnny5.9

That's what I was thinking. If I hear back it's cylinders I'll just buy new ones and install them myself.

cLAYH

When a cylinder is bypassing like that the fluid slipping past the seal causes a heat build up. Cycle the dump a few times a hold it over relief on the stops then feel the cylinders, if one(or both) is warm or hot thats your bad cylinder. I diagnose bad cylinders on skid steers like this.