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Did I find my problem?
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tedbear
Posted 4/9/2020 11:51 (#8175979 - in reply to #8175405)
Subject: RE: Did I find my problem?


Southern Minnesota Between Freeborn & Wells
With rephasing cylinders they MUST be two different sizes to keep them in phase. When oil goes into the base of the first cylinder it pushes oil out its rod end. This oil goes to the base end of the next cylinder. The oil coming out the rod end goes to another cylinder or back to the tractor.

The area of the piston on the base side of any cylinder is larger than the area of the piston on the rod side due to the size of the rod. This is because the rod itself takes up space. If enough oil were pumped into the base side to move the piston 1" the oil from the rod side would get pushed into the base of the next cylinder. Its base should be smaller than the base of the first cylinder. If the cylinders were the same size, the second cylinder wouldn't move the 1". Ideally the base of the second cylinder should be the area of the rod end of the first cylinder. If several cylinders are plumbed together in series for rephasing, each succeeding cylinder needs to be smaller.

We demoed a new tillage machine one time. It was just put together and we were the first to use it. It had two cylinders on each side. So each side had a rephasing pair. It did not raise/lower evenly. The salesman was trying to adjust some mechanical linkage when I got there. He could get it to be level in the field position or the road position but not both. I followed the hoses and noticed that the first cylinder of the pair was the smaller one. Salesman said "shouldn't make any difference". It was easy to swap them with out moving any hoses so they eventually tried switching the cylinders. This solved the problem. Salesman said he had never heard of that. I said apparently the set up man never tested it.

All "air" must be removed internally for this to work. Some cylinders have a "leak" passageway so that when the cylinder is fully extended or retracted oil can flow internally so as to even things out and bring them into phase. The Master cylinder on some Deere planters had a collar that could be removed. Then the cylinders would retract a bit further to uncover this passage way to let the oil even out. When it was back in phase, the collar was reattached to prevent the cylinder from retracting into that area for normal operation. With other systems holding the hydraulics for a while at the end of the stroke will push the air past the piston and eventually it works out. I've seen situations where the hose needed to be loosened a bit at the cylinder so it leaked a bit to get the air out. Once the cylinders were in phase then the hoses were tightened.


Edited by tedbear 4/9/2020 11:56
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