Posted by NCWayne on August 28, 2012 at 20:12:47 from (126.96.36.199):
In Reply to: Dynahoe 190-4 posted by Erich Boehm on August 28, 2012 at 06:41:38:
If it has a lock valve in the line , and the seal on the piston fails it will do exactly what you are talking about. I just repacked an outrigger cylinder on a customers bucket truck that was doing exactly what you are describing, and a bad piston seal was the culprit.
It can go down because there is more surface area on the back side of the piston than the rod side (due to the rod taking up space). As a result of the extra space the fluid going into the cylinder will pressurize it enough to push it down, and displace fluid from the rod end to the tail end. There is just enough pressure differentialgoing that direction to make it move out and displace the fluid past the piston. Going the other way, because of the different size area the pressure has less area on the rod end to act upon vs the tail end, and unfortunately the displacement of fluid, and lack of differential pressure, keeps it from building enough pressure to cause the lock valve to unlock and allow the cylinder to raise.
If you need to get it up you can break the lines loose and use a jack, another machine, etc to put pressure on the cylinder in the up direction. This should unlock the valve and allow the cylinder to rise with the applied pressure, but it will usually drop right back down when the pressure is taken off of it, but at least the cylinder is no longer pressurized and can be removed to be rebuild. Good luck.
Fast Shipping! Most of our stocked parts ship within 24 hours (M-Th). Expedited shipping available, just call! Most prices for parts and manuals are below our competitors. Compare our super low shipping rates! We have the parts you need to repair your tractor. We are a company you can trust and have generous return policies. Shop Online Today or call our friendly sales staff toll free (800) 853-2651. [ About Us ]
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.