Gravity Hydraulic Cylinder Requires Pressure to Return to 'Home' Position

[r8f1k]

I got my cider press up and running, controls are good, etc. The cylinder is rebuilt with a new gland. The problem I have is that the cylinder is single acting and the return goes back through the same hose as the pressure, therefore it is VERY slow to return and needs help to return to its fully retracted position. The cylinder needs to be all the way down in order to load another batch of cider pomace and racks. There is a large cast iron support with a 4 inch thick piece of maple on top of the cylinder when it is empty, probably 300lbs. So far that is not enough to get it to return......I am about 2 inches from where it is supposed to be. Any thoughts?

 

[ptsg]

Can you add some big springs to help it retract?

 

[Leejohn]

Yes I do, put a tee in the line . Then a manual valve in the tee line and run back to the tank at the fill. On my dump trailer I use a 12v valve . The valve I use you can also use 120v ac coil. With the manual valve all you have to do is just open it and it well come down by itself, Just don't forget to close it so that you can open it.

 

[oldnslo]

I believe in your other post you stated the cylinder is a 10 inch diameter if that is true 300 lbs weight equals approximately 4 PSI so any restriction to tank in the return line will cause it to stop lowering.

if the new seal or gland is a little tighter the extra friction will also cause it to stop moving

 

[r8f1k]

I am using a 12vdc tee selector valve to control up and down. De-energized, it allows pressure to push the cylinder up and energized, it shuts the pump off and opens to allow flow back to the tank through a filter. I'm sure that the gland is tighter than what it was 100-120 years ago. As I understand it, from the hydraulic shop, it was wrapped packing, similar to graphite packing on a water valve. He made me a new gland out of an off the shelf unit and they cut it down to fit. They took off about 1/8" to get it in. Doesn't leak, but it might be too tight compared to what it was. There is a ring that holds the gland in place with 8 bolts. Initially, the cylinder would not retract at all. After closer inspection, the ring was slightly askew and prevented the gland from being parallel with the cylinder. I loosened all the bolts, made a gauge and turned each bolt one flat at a time to level it out. I'm tempted to back off one flat on each bolt to see if that helps. Thoughts?

 

[oldnslo]

Pressure will help seal the gland while raising but it must originally be snug to seal so yes I would carefully loosen the bolts if the gland is still tight in the bore.

Might also want to double check to see if the cylinder bore is larger once raised a little ways since machine does have a few years wear on it.

 

[r8f1k]

Here are some photos of the press cylinder

 

[oldnslo]

R8
Are those pictures with the press fully open or closed?
If closed it looks like the bottom of the shaft or piston could be covered with corrosion and be slightly rough vs a nice smooth polished surface. If rough surface this would create extra friction preventing press from opening fully

do not polish or sand off rust preventing finish though.

 

[r8f1k]

It is not fully closed. Some of the piston has rust on it, the piston does not have any plating. The surface is still quite smooth, I have wiped it down extensively with scotch bride pads. I'm betting it is a tight gland.....

 

[r8f1k]

oldnslo, you were 100% correct! Even though it looked smooth, it was not. I took a grinder with a light wire brush and cleaned it up really good. It wasn't really a solid bit of rust, it was that corrosion that just kinda swirls when hit with a brush, but you can then wipe it off with a paper towel. Immediately after doing that, it descended just as it should.