floor jack goes up ok but won't hold

I have replaced the o-rings and replaced the hydro oil pumps up a lot better than before but will  not hold also how to adj the air the one you are not to mess with 

seandogue9 months ago

Also, check the pressure release and fill port. My dad had a really old (circa 1930s or maybe 1940s..big thing, about 4 feet long) floor jack whose pressure release(located on the drag handle) wouldn't fully engage, and one time, after replacing the hydraulic fluid the fill port was a bit loose

iceng9 months ago

I agree with cerberustugowar

that it is leaking past a return valve where the tiniest bit of dirt will disable the unit.

is it an air over hydraulic? or just a regular floor jack?

maybe it's leaking past the return valve or maybe there is some sort of damage to the barrel?