Unfeathering accumulator

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Skyknight320

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Skyknight320
I have unfeathering accumulators on my Cessna 320 and one of them is not functioning properly. It holds 120 PSI of air and does not leak, but when unfeathering the prop it looks like it tries to unfeather, but does not and all the air is then gone in the accumulator canister. I have not noticed any oil leaks in the system, what would cause it to hold air pressure unless unfeathering? I mean if there is a leak, wouldn't it not hold air pressure at anytime?
 
Just because the accumulator itself isn't leaking doesn't mean there isn't a leak elsewhere in the system. Most folks I know got rid of their accumulators and just hit the starter with the prop lever forward.
 
Yes that is what I did to unfeather it, probably not worth fixing, but I am training my son to get is multi and it sure is a nice feature to have.
 
Skyknight320 said:
Yes that is what I did to unfeather it, probably not worth fixing, but I am training my son to get is multi and it sure is a nice feature to have.
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Understandable. But I guess my response would be: train him how to handle malfunctions!

When was the last time you had your propeller overhauled? Would be a perfect time to check the rest of the system for leaks
 
I suspect you have a leaking unfeathering valve. Don't know how the 320 is set up. Sometimes the valve is a component of the governor, and other times it's an external valve. Anyway, the accumulator has an air charge, and this air gets compressed by the oil from the governor. When the prop control is in the feather position, the oil under pressure in the accumulator is "bottled up" by the valve. If the valve is leaking, it will drain this oil off and it won't be available to unfeather the prop when needed.
 
Both the prop and governor where overhauled a couple years ago, but this is the first time I tried to unfeather since. I don't recall ever seeing an external valve so it must be in the governor. I assume oil would be leaking too because if the air can get out so can the oil.
 
The oil may or may not be an external leak. It could just be bleeding off thru the prop circuit and going right back to the sump, and you'd never see anything.
 
So the accumulator itself might have the leak even though it holds air if not feathering the prop.
 
Is the pressure you're seeing just the precharge. Typically accumulators have two chambers. Air never touches the oil.
 
Yes the accumulator has a placard that says 120 PSI around the valve steam. This pressure was 0 after unfeathering. The accumulator on the other engine worked and the PSI remained at 120 after unfeathering.
 
Maybe the air is leaking past the seals inside the accumulator chamber?
 
Or around the air charge valve. A little "leak check" (soapy water) would tell that tale.
 
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