Has anyone had any experience with on line condition monitoring of N2 filled Buna-N bladders in oil filled accumulators? We have these on governor systems and the manufacturer recommends draining the oil to confirm the N2 precharge pressure every year. Its understood that the Warning Time is very short so a bladder could fail shortly after the precharge pressure was confirmed and the test would likely reduce the fatigue life of the bladder. There are 6 pairs (bladder accumulators attached to a N2 bottle) in a bank so there is redundancy, we can let one fail and still provide the functional requirement. We are looking for a remote method of determining that one bladder has failed. They are 2000 psi systems.
We were thinking that after the bladder failed the oil would absorb some of the N2 at pressure then release it in the sump. Would a N2 sensor in the sump work?
THX

I remember we serviced oil accumulators every plant shutdown. Anyway, just curious why do you want to remotely determine the bladder's failure because you already have a redundancy?

Two thoughts based upon using ultrasound:
1.You could test the integrity of the bladder with much lower pressures by using compressed air and a portable ultrasound system
2. You could also use a similar ultrasound system to listen for leaks in operation either using a portable or on-line system.
I suggest that you contact SDT at http://www.northamerica.com

Thanks for the comments guys.
Josh - the problem is to sense when one bladder has failed and hence we have lost the redundancy. The functional requirement is based on an extreme event which does not happen too frequently, however if there was a method to sense that it had failed we could dispatch crews to make the repair with the system in risk condition for a minimum period of time.

Tom - I'll try that link. I'm not sure if the "sound" of a failed N2 bladder accumulator (gas acts on the oil directly)is different from an in-service one where the N2 acts on the oil via the bladder.

Larry, we have N2-charged oil accumulators in some of our mobile plant. Normally they provide secondary steering and braking thus are considered critical. Ours are precharged to 1500psi with N2 and the accumulator charging system cuts out at 3500psi oil pressure. Here are a few comments.

1. In our experience, a bladder is either perforated or it is not. We have not seen a reliable method of monitoring bladder condition, however our failure modes might be different. The issue, similar to yours, becomes one of detecting a failed bladder.
2. One of the systems we have automatically bleeds the oil from the accumulator on engine shutdown (via a solenoid driven by the control system) to minimise risk to techs from stored energy.
3. The hydraulic tank sight gauge is marked with "FULL" and "ADD" for both engine running and engine stopped. Our pre-shift walkaround inspection routine includes a task to check oil level on the hydraulic tank with the machine engine running. When the engine starts the accumulators are charged. The oil level in the tank drops as the accumulators are filled. If a bladder is perforated the oil level will be below the "ADD" mark on the tank.
4. When we have had a bladder perforate, the rapid discharge of gas into the oil (and a few litres of oil in the return line) pumped oil back into the tank breather. It then clogs, and refuses to expel the nitrogen quickly. The result is a distorted tank. In our case, an N2 sensor would only confirm what we can see.
5. We also have an oil pressure sensor to determine when the accumulators need to be charged.

I'm probably not understanding your system, but it sounds like the accumulators remain permanently charged to provide governor control. Do these accumulators cycle much in service? Or are they charged and ready as an evergy source in case of some other system failure?

Perhaps you could use similar concepts, either tank oil level (either visual inspection or a sensor), or a system oil pressure sensor to detect an oil pressure drop if a bladder fails?

Regards,
Matt.

How long does it take to replace the failed bladder?