> I think Leon is correct, the pressure is constant in a J
John, I don't understand. Are you saying that a variation from 20 psi
disengaged to 350-550 psi engaged qualifies as "constant" ?
Or are you saying that I, the ROM and my pressure gauge are all wrong, and the
pressure doesn't drop to 20 psi when a J-type is disengaged ?
> - any J type that has a delay of a few seconds is not as it should be.
Just to be clear, mine does not have "a few seconds" delay. It might be only
0.1 second, I've never actually tried to measure it. But it is very definitely
longer than my A-type, which will be engaged before I hear the click of the
switch. Perhaps there is something wrong with it, but it's been freshly rebuilt
and my friends with stock J-types say theirs do the same thing.
The OD pump has a very small displacement, and only works through 1/2
revolution. On a disengaged J-type, the pump output pressure is relieved to 20
psi, not nearly enough to move the operating pistons. Ignoring all the other
things that have to happen first, even if the relief valve closes instantly, the
pump still has to pump enough oil to move the operating pistons from their
released position to their operating position. Certainly how far that is makes
a big difference. But even if there were no distance at all (which is
impossible), it could still be as much as 1/2 driveshaft revolution before the
pump starts producing any output whatsoever and hence before the pressure even
starts to rise.
By contrast, an A-type has operating pressure stored in an accumulator all the
time. Even if the pump were not running at all, the high pressure oil from the
accumulator is enough to instantly engage the unit when the operating valve
opens.
Randall
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