air lock? How do I bleed hydraulics?

[J_J]

Question. If a cyl piston seal never goes past the port opening, is it possible for an air bubble to be trapped at the ends of a cyl, especially with the ports mounted down?

 

[AKKAMAAN]

how do I tell the difference between pressure line, and return line on each cylinder?

If cylinders are double action, both cylinder lines have to be high pressure rated...

Return or pressure line to a double action cylinder, will depend on wether the cylinder is extending or retracting...

All spool valves always direct flow from pump to cylinder, the same way.

Work port closest to lever gets flow from pump to cylinder when spool is pushed in by lever, and same port will send oil from cylinder to return, when spool is pulled out by lever....

 

[JoelD]

Really doubt it is air, the system is ultimately open to the air and continually "bleeds" it's self.

Maybe something got into the valve body?

Pressure guage is best way to check.

Be careful, high-pressure oil can do some real damage to skin.

Joel

 

[AKKAMAAN]

Question. If a cyl piston seal never goes past the port opening, is it possible for an air bubble to be trapped at the ends of a cyl, especially with the ports mounted down?

No cylinder is designed so piston seal can go past the port opening!!

I have never ever had to bleed a cylinder, no matter how it is mounted....

All connections in a hydraulic system are designed to seal for hydraulic fluid.
Air is a GAS, and no hydraulic flange seal or even o-ring seal will hold back GAS at max hydraulic system pressure.

If cylinder is vertically mounted ROD DOWN, yes it is possible for a a FEW cc to get trapped for a while, but that wont show as a total loss of motion on a normal cylinder...

Cylinder mounted ROD UP, always bleeds air easily by the piston and gland seals


Horizontally is probably the most critical position, will trap some smaller amount of air if work ports on cylinder are positioned down...

trapped air can never "lock up" a cylinder, only slowdown the response of the cylinder, till air is pushed out of the system.....
Under high pressure air will compress to almost zero volume, and decompress when pressure is reduced...