Hydraulics on Post Driver

[tinygiant]

Hello again all...

I have an old post driver that I rebuilt. It's one of those types that has a large I-beam that lifts up with hydraulics and drops by gravity assisted by springs. I've been using this successfully for several months; however last night while driving a 6" post for a fence, the I-beam/weight started slowing down half way through the travel. There were no metal scraping noises or anything externally obvious as to the cause. The only thing I can think of is an issue with the cylinder. The fluid is fed from a standard rear remote and lifts the weight with no problem. The fluid is dumped via a hose routed directly into the hydraulic fill port. Again, this has worked just find with no issues until yesterday. Currently, when at full height, the I-beam/weight will dead drop as it always did until about half way down its travel. Half way down, it starts to slow considerable and essentially provides no work to driving posts. I've confirmed that all the hydraulic lines are clear, the fluid level in the tractor is correct, the valve on the driver appears to be working correctly, there are no visible hydraulic leaks on the tractor or the post driver. Just for good measure, I've also greased/lubed all the glide wheels the I-beam rides on. I've moved the driver up and down with no externally-visible interference or binding in any parts. This leads me to believe that the cylinder has to be the culprit, but with such a simple single-acting cylinder that was just rebuilt and worked flawlessly, what could possible be the issue with it? Also, for good measure, if the cylinder was good, what else could be going on the with it?

Thanks for any help or advice you can provide. I'd be happy to answer any questions to get this machine back up and running.

 

[Birdhunter1]

I would be willing to bet the hose from the valve on the driver to the cylinder is collapsed, not collapsed when raising but when it goes to dump I bet it is restricted. Assuming that you checked the hose to your trans fill and you have flow, your valve could be blocked but first thing I would guess is that hose.

 

[tinygiant]

Thanks! That's a good idea. It's a thick-wall hose and very rigid, but I didn't check to see if it was collapsing on discharge. There is definitely flow back into the tractor fill port, just not quickly. I'll check that hose today.

 

[tinygiant]

Unfortunately no collapsing on the feed/return hose. I just finished taking the valve apart and found a crush/crumpled washer on the return stroke, preventing the spring/valve from moving full length. I'm going to find a replacement and see if that's the problem.

 

[RNeumann]

Hose is a great idea. Is the dump valve able to flow all it needs to? Lift it, disconnect the hose or ? after the dump valve and see what happens. If it works properly it’s the hose or something down stream. Otherwise it’s in the valve or before.

 

[tinygiant]

All, thanks for you time. The wifey and I figured it out. We took the feed/dump valve on the driver apart and found a mangled washer that wasn't allowing the valve to reach the full dump position, even though it did allow the valve to reach the full feed/fill position. We put a Grade 8 washer in there to prevent the same failure in the future and now it works even better than it was before the washer failure ... so I guess the washer has been failing for quite some time. But, all better now. Thanks again, this place is great!