Wood Splitter Hydraulic Problem

JC · Post by JC » Tue Dec 01, 2009 7:59 am

A wood splitter has got to be the simplest hydraulic system there is, but this one is giving me fits. It has an 8 hp air-cooled engine, that drives a 16-gallon per minute, 2-stage gear pump. A spool valve, with a pressure-relief controls the 6x24" cylinder. The high volume part of the pump moves the oil until the cylinder meets with resistance and the flow is diverted to the low volume side of the pump at 650 psi. It will pump about 2200 psi at 3.5 gpm. This set-up has been working fine for the last 20+ years.
A couple of weeks ago I was trying to split a piece of black oak with a big knot in it and the cylinder just stopped moving. It has never done this before. With 2200 psi on a 6” piston it will split anything.
I put a pressure gauge on it and bottomed out the cylinder. It read 500 psi. I tried adjusting the relief, but the pressure didn't change. I disconnected the pump and tank hoses from the valve and installed a ball valve between them. I started the engine and slowly closed the ball valve while watching the gauge. When it got to 1500 psi, I opened the valve and shut the engine off. OK, problem solved. Its in the valve. Maybe a bad PR or maybe a scored spool, but its in the valve. I put a different valve on it and tried again. Still only 500 psi. The PR on this one is not adjustable, so I shimmed the spring. Still only 500 psi. Then, I thought that I must have mis-diagnosed it when I tested it with the ball valve. A worn pump will give a higher reading when the oil is cold, like it was when I tested it. Instead of testing it again, I just put a new pump on it. Now it has 600 psi. I think that I probably just replaced one bad valve with another one. What do you guys think? Any suggestions?

RossM · Post by **RossM** » Tue Dec 01, 2009 8:18 am

Could it not be as simple as the Ram seal has blown under the strain of splitting the black oak knot?

Jerry Coles · Post by **Jerry Coles** » Tue Dec 01, 2009 12:26 pm

I would try connecting another Hydraulic ram to the pump / valve and see what readings/action you get.
I would tend to follow RossM's train of thought.
Do you know if there is a flow of oil into and out of the ram? Slackening the outlet pipe connection could show this.
A set up that old could be showing some deterioration of seals.
Cheers
Jerry

JC · Post by JC » Wed Dec 02, 2009 3:02 am

Ross and Jerry,
It looks like you have found the problem. I was taught (by a guy that owns a hydraulic repair shop that employs 40 people) that due to Pascal's Law, a cylinder will still extend and build pressure, even if there is no seal on the piston or even no piston at all, as long as no fluid is escaping from the cylinder. I guess that he was wrong. I unscrewed the hose that runs from the valve to the back of the cylinder, and plugged that port (on the valve). When I moved the lever, the gauge read 2500 psi, before it started dumping over the relief.

JC · Post by JC » Wed Dec 02, 2009 7:18 am

JC wrote: as long as no fluid is escaping from the cylinder.

OK, I feel stupid now

Of course there's fluid escaping. It's going out the hose at the other end of the cylinder, through the valve and back in to the tank, just like its supposed to! The hydraulic shop owner wasn't wrong, he was talking about a single acting cylinder.

I can still split most of my wood with 600 psi. When I'm done with that, I'll take the cylinder apart and re-seal it.

Mark · Post by **Mark** » Wed Dec 02, 2009 6:28 pm

JC,
I was working on and old D8 many years ago with this kind of problem, we had to change the packing and seals. I found that the hyd tank was full of packing, and the filters. Your splitter probably doesn't have packing anything like a Cat, but it being as old, it may have something similar. If it has a filter, it may be clogged with the old packing. How long has it been since you changed the hyd oil? I always was a firm believer that hyd oil didn't need changing, until I bought my Kubota. After the warranty ran out, I didn't change the hyd oil one year and my pump started making noises, I called the dealer and talked to a mechanic, the first thing he asked me was how long has it been since you changed the hyd oil. Well a long story short I changed it and my problem went away. I guess all the equipment we had, had hyd oil leaks and oil was added most everyday there by wouldn't have had time to get old.
Back in the day they wouldn't let you fix anything until it stopped, now we live in a different day and this probably wouldn't be the case.
How did you get the nut off the ram? Sometimes we had to use a cold chisel and 3 pound hammer, if this didn't work we got a bigger hammer

Hope you get it fixed.

JC · Post by JC » Thu Dec 03, 2009 7:26 am

Mark
My old piston seals had to go somewhere, so they have got to be in the hydraulic oil. Hopefully the filter caught most of it. I'm not too worried, though. Since I have a gear pump, those pieces of packing won't hurt it much. I don't use the splitter much, so I only change the filter once a year. I should put a gauge on the filter, so I know when to change it. That's a good idea for any hydraulic system. I usually don't change hyd. oil unless it gets contaminated or a hose breaks and it changes itself. I think that I'll pull a sample off the bottom of the tank, and see what's in it.
The way that I get the nut off the piston is to clamp the eye on the end of the rod in a big press and use a 1" drive air gun on it. If that doesn't work, a 1" drive breaker bar and a long, long cheater. In the field, its a little different. It usually involves a vice, an acetylene torch, a block, a chain, and the breaker bar.