From time to time every hydraulic shop "confronts" an accumulator bearing an
"exclusive" gas charge port. Although most of the hydraulic
population already know how to deal with the "outstandarted", I still
occasionally see puzzled faces when there's a need to check the
pre-charge pressure of such an outcast. With most accumulators the reading is simple
- you use the normal charge kit. But what if
you don't have the necessary accessory to couple to the gas charge port?
Well, it is not difficult at all!
The easiest way is to install a
pressure gauge into the accumulator feed line, then to pressurize the
accumulator to the point when some oil gets in,
and then to drain the oil SLOWLY while constantly
monitoring the pressure gauge. When the bladder fully expands and the
oil flow from the accumulator stops, there's an abrupt
pressure drop in the feed line (most easily seen on a needle-type gauge). The
pressure drop point indicates approximately the pre-charge pressure.
Often it is possible to perform this pre-charge
check without dismounting the accumulator from the machine, as
normally the accumulator can be pressurized by the system pressure,
and the manual safety discharge valve (when equipped with one) can be
conveniently used for the "slow depressurization" purposes. If you are
lucky enough, the accumulator line will have a test port already
installed. If it does, pinch yourself to make sure you are not
dreaming... (this is my way of saying that hydraulic installations
should have pressure test ports installed during the construction, test couplings are NOT a waste of money, people!!!)
Another advantage of this method is its non-invasive
nature, which can make a difference for very small accumulators,
which loose relatively large part of pre-charge every time a direct gas
pressure measurement is performed.
Although this method doesn't provide reading
accuracy of direct gas pressure measurement, it is 99 times of 100
accurate enough .
This short video is just a workshop example of how it's done.