Health of a Hydraulic Accumulator
Health of a Hydraulic Accumulator
(OP)
Is there a way to determine the condition of a bladder in a Hydraulic Accumulator without taking it off-line? If not, how would you know if it were ruptured until the Accumulator is needed... and it's "not there"? Thanks





RE: Health of a Hydraulic Accumulator
Have you looked at your hydraulic accumulator recently? It normally should have a Nitrogen pressure gauge monitoring the gas side of the bladder. This pressure will indicate if you have any inert gas on that side in order to "absorb" the pressure shocks - or if you've lost that gas due to leaks or ruptured bladder (diaphragm).
Art Montemayor
Spring, TX
RE: Health of a Hydraulic Accumulator
When the accumulator looses its charge or ruptures the pressure usually starts to fluctuate, unless it is installed as a standby unit.
RE: Health of a Hydraulic Accumulator
If the bladder is ruptured the gauge will still read the "process pressure" correct? Thereby leaving the impression all is okay.
If it does rupture, the nitrogen charge will eventually "work its way out" as its absorbed or entrained in the process fluid, correct? Leaving the Accumulator full of fluid.
RE: Health of a Hydraulic Accumulator
A quick method to check the N2 precharge is to watch the oil side pressure when the system is shut down. It will slowly decrease as the oil is bled off, until the precharge setting is reached. At that point, as the last drop of oil comes out of the accumulator, the bag hits the steel, and the oil side gauge will drop abruptly to zero.
This assumes you can somehow remove the system load, gravity loads, etc from devices held up by the hydraulic system. Otherwise, the pressure will drop to that of the heaviest static load being held up by anything still connected to system. It will hold that pressure as the load slowly lowers, then the pressure will start decresing again.
On systems that keep the accumualtor on line, but slowly bleed it off, you will have to know what loads are on, or possibly cap off the system and just have the accumulator and pump and bleed valve in the circuit.
On systems that take the accumulator totally off line at shutdown, then bleed it down separtely to tank, it is very easy to see this abrupt drop.
In either case:
1. Get a gauge right near the accumulator, before any bleed down or safety valves.
2. Power up the system. Oil pressure on this new gauge should be equal to system pressure.
3. Shut down the pump. Accum is now bleeding off to tank.
4. If oil pressure drops immediately, the N2 is all gone, the accumulator is a big steel tank full of oil.
5. If pressure decays slowly, but abruptly drops to zero at some value, say 900 psi, then that value is the N2 precharge pressure.
This is a quick field test, not to be relied upon as an exact pressure. i.e. if reading 900, I could actually have 750 or 1200 psi, but at least I know there is N2, and approximately its precharge value.
We try to get the operator to keep an eye on the system preessure gauge each time it shuts down, to catch problems early.
kcj
RE: Health of a Hydraulic Accumulator
kcj gave a fast way to check and it even works on running circuits if there is and isolation valve at the accumulator inlet. After discharging the oil make sure to upen the isolation valve slowly until the accumulator gets up to system pressure so there will not be a big pressure drop on refilling.
I have a demonstration of this fast, non-invasive pre-charge check on my web site. It is a Power Point presentation and though it runs slow on the web it runs like a movie from a hard drive. www.fluidpower1.us
Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us
RE: Health of a Hydraulic Accumulator
A method that I have used (from the surge tank vendor) is the installation of load cells on the tank, the tank will need expansion joints on the piping and two load cells (on a four legged tank). With the bladder in a known good condition, operate the system through its entire range and note normal operating weights, if the bladder fails, the tank will get heavier as the gas is replaced by the liquid this increase in weight will be gradual as the assumed failure mode of the bladder is a pin hole or small tear. Load cell monitoring can be done in any number of methods, electronic, connection to SCADA, or simple dial indicators with markings of normal operation. The load cell will also tell if there is too much precharge, in that the weight will not change as much as normal operation.
Hydrae
RE: Health of a Hydraulic Accumulator
You make very good explanation on determining accumulator condition.