[Shop-talk] air over hydraulic bottle jacks

[Karl Vacek]

As unsophisticated as you'd expect from Horrible Freight.  Usually the 
pistons are coaxial, but the photo shows that it's as you describe.  They 
just added an air cylinder to a manual jack.

In typical air over fluid (not literally, it's just what they're called), 
piston pumps, the air cylinder is double-acting.  And they DO soundlike a 
slow jack hammer -- they're very similar in operation.

Valving triggered by the piston reaching either end of the stroke flips the 
supply from one side of the cylinder to the other, ditto (but reverse) for 
the exhaust.  This one may be simpler, with a return spring for the air 
piston.

Karl


> Actually it seems like the air piston assembly just "pumps" the original 
> hydraulic pump plunger up and down. So the air enters the cylinder and 
> pushes down on the original plunger [or something close to the original 
> plunger] until the air piston reaches a relief port. Then the air piston 
> retracts and then takes another shot at the hydraulic plunger. It really 
> is just "doing the pumping" for you. It sounds like a very slow jack 
> hammer when it works.
>
> Hope that makes some sense,
> Arvid