When I returned to the jack, its ram wouldn't raise at all anymore.
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These jacks all have a fill plug on the side of the reservoir jacket somewhere. Here's a close-up of this one's.
It looked to me like this could get messy, so I arranged to do the filling on my oil change drain pan. The only funnel I had that was near small enough was my Coleman camp stove fuel funnel. I took out the funnel's filter element for this.
I tried a procedure known as 'priming'[3]. To 'prime' a jack, you close the release valve, manually raise the ram to its full height, open the release valve and push the ram back down. That had no effect.
The jack was behaving exactly as if its release valve weren't closing fully. I unscrewed the valve stem completely and took a peek inside -- there was no check ball in there, and it sure looked as though there ought to be one. Here's a shot of the valve stem, along with a 1/4" diameter ball bearing I got from my stash of bicycle parts.
I reassembled the valve with the ball inside and the jack worked.
Here it is under a Ford Ranger behaving like a jack.
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Storing a Jack
An idle jack should be put away with its ram fully collapsed, so it's protected from rusting, and its release valve closed, so it can't leak.
The 'seal' around this jack's release valve stem is only as effective as it needs to be, which is to say 'not very'. If left unclosed, the release valve will leak oil. That's no doubt how this jack came to be empty -- with the release valve's check ball missing, oil had a slow leakage path out past the marginal seal.
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Notes:
[1] 'ISO' stands for 'International Organization for Standardization', which has a rather Orwellian ring to it, don't you think? (And they seem to be a bit 'letter-order' challenged.) I'm led to believe that the 'AW' stands for 'All Weather'. The '32' is an ISO viscosity number.
[2] Nothing is ever as simple as it looks like it ought to be.
When a funnel's spout is a snug fit in a vessel's only opening, the air inside the vessel can't escape as liquid is poured in. Liquid fills the funnel's spout and backs up into the funnel.
Some funnels have a self-venting feature.
A solution is to drape a little piece of telephone cabling wire over the neck of the jug, or whatever, that is being filled, so the spout doesn't seat.
[3] What priming allegedly does is it draws oil from the reservoir through two check valves and their passageways, presumably purging any air that might be interfering with the hydraulics' works. I'm not sure I understand that, but that's what priming allegedly does. Anyway, there's a pretty good animation of a jack's operation here.
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