Re: Hydraulic Ram purging - How does that work?

Posted by Dieselman on April 24, 1999 at 00:30:19:

In Reply to: Hydraulic Ram purging - How does that work? posted by Tim Collins on April 23, 1999 at 18:56:30:

Tim......I'll try to see if I can explain the theory to you. Oil will not compress and so when you open the valve to let the flow of oil from the pump enter the cylinder It will force the air out of the cylinder by pushing the ram. Realize that not all the air will leave the system right away. The better part will but realize that some will still be in the line and won't be flushed out right away because the ram has stopped at the end of it's travel. Then when you pull the valve in the opposite direction the flow will change and push the ram the other direction pushing oil and air from the other side out. Eventually enough times of back and forth full travel and the oil will remain in the system and the air will have been pushed into the resevoir and escaped. Not all the air will remain in the resevoir realize because there is not enough space for it all obviously so that's why there are breathers on all hydralic resevoirs of some sort or another. The oil is heavier than air and that is also another reasoning that it stays in the cylinder instead of the air.
I'm assuming now this is not a single stage cylinder you are talking about. With only one hose leading to it and gravity playing the role of making the cylinder pull in the opposite direction of lift.
A dual stage cylinder which is what I'm referring to has oil on both sides of the ram which force it back and forth for pull and push effect. As DC mentioned, while purging the system check the resevoir often to make sure that you haven't pushed all the oil out of it into the cylinder and all you are doing is recycling air.
I hope this has helped somewhat and hasn't confused you more. I do have one question for you though.......Is you system that you are hooking the cylinder to a closed center hydralic system or open center hydralic system? Shouldn't make much of a difference on purging the cylinder but makes a difference on how much available pressure you will have for it and how fast it works. I wish you Good luck!!!

Respectivly
Dieselman

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