Hydraulic Cylinder Bleed Valves?

I use something like this.. Normally has a steel wool filter crammed in the end, and a loose cap to keep the dirt out... Like you put on the axle of a car to keep the differential from building up pressure as things warm up..... i have a couple on the wing cylinders of a BatWing mower.... POWER UP, and float down.. If you get any internal leakage past the piston seal, this will let it leak out.. Also lets air go in/ out as you raise/ lower.

Back in the day single acting cylinders had a valve in the non-pressurized end - you see this a lot on old loaders without down pressure. I never really got why they put a valve on there instead of a breather. I don't think they weren't so much 'bleed' valves, as they were to be left open so you didn't build air pressure in the non-pressurized end. Possibly they were meant to be left open, unless operating in a dusty environment and not using the loader, in which case they could be closed to keep dust out, which would also keep them from bouncing around a little (say, for instance, bouncing around a dusty field doing field prep work). That's just a guess, however. Alternatively, maybe they were to let fluid drain out that leaked past the piston seals. We had this on an old Wagner loader with single acting lift cylinders on a Cockshutt 540 - even when the cylinders were new, the crappy V-pack seals in the cylinder would bypass some hydraulic fluid, so you had to crack open the valves every few months and run them out to full stroke to get rid of the bypassed fluid. Otherwise it would build up in the rod end and prevent you from reaching full stroke.

Edited by DanielW - 01 Aug 2023 at 7:34am

Gary wrote: Is a 'Bleed Valve' and a 'Breather' the same thing on a Hydraulic Cylinder ? G

So,…..are you guy saying that a single acting cylinder, without a breather, is designed so that it doesn’t stroke until the end, so the dead space air doesn’t compress a significant amount? In which case I would think you’d need a bleed valve because a little oil will get by and take away from that volume and you’d lose lift and function.

Got a few dump forage boxes set up single acting. They have vent/ breathers, but can be plumbed double acting and stroke pretty much full length.

If you single cylinder has a ROD that is basically the same size as the cylinder BORE, then you probably dont have a vent.. You are not worried about "leak by" since there is not enough surface area on the back side to counter act the oil pressure on the PUSH side... this is what happens on a porta power, or 3 point cylinders like a B-C, or WD 45..

Gary wrote: DF Are you referring to a Bleeder Screw located on the hyd. pressure side of the cylinder, loosen to bleed air out of the oil system? Or to a Breather on the non-pressure side of the system, to allow air to enter and exit as the cylinder operates? G

most disks you raise, then drop a pin thru a link by the cylinder... then take the pressure off the cylinder, then disconnect from the tractor.. Hydraulic pressure is not used to hold the disc up when parked...

Edited by steve(ill) - 02 Aug 2023 at 12:29pm

For future reference, I advise to buy hydraulic spools with NPT thread from the start. Buying all the adapters from SAE and BSP thread to convert ain't cheap and some are really hard to find.

Edited by dfwallis - 04 Aug 2023 at 11:41am

Jim.ME wrote: A single acting cylinder would work and lift the disc for transport, but the ones I have seen use double acting cylinders to lift the transport wheels clear of the ground when in use.