[yellowjacket]

when a single ended ram is fully extended(piston out)your fluid level in your resoivoir drops becausethe fluid volume is now in thecylinder. when cylinder is fully collapsed(piston in) the fluid fills back in the resoivoir which will always be when the resoirvoir is "fullest". if u dident have any vent the resoivoir would go into a vacume when cylinder is extended and wouldgo into a positive when cylinder is collapsed (talking about the air space in the resovoir).


on a double ended ram as the piston collapses on one side it extends on the other so theram actually holds close to the same amount of volume at all points of stroke except at full lock both ways and even then it dosent change drastically. so the fluid in the resoivoir dosent move up and down as drastically, so the air gap between fluid level and cap dosent change as much. you still have some movement and as mentioned expansion as fluid gets warmer.

single ended could get by with a bellows but it would have to be huge..never seen one big enuff. im sure if u had one and did lock to lock it would look quite vulgar :)

a lot of rigs that dont think they are vented with a single ended ram actually have some leakage in the cap or resorvoir(thereby are indeed"vented")