Aux hydraulic pump question on a 500B.

[lesnagy]

What is normal behavior for the aux pump only pressure reading? Mine brings it to 500psi then it rapidly drops and then back to 500psi over and over. When I have any engine running its a solid 1000psi without fluctuation. Is this normal or do I have a leak somewhere. I don't think I am loosing fluid but haven't put many hours in the air yet. I may still have to bleed the lines since my last leak fix.

[ghancock]

Well, they say if it won't hold the pressure after pumping up then there is a leak somewhere.  However, if you don't have fluid leaking out and the flaps will go up and down then I'm not sure I'd worry about it too much.  Mine does same thing but hasn't been much of an issue. 

Just my 2 cents,

Glenn

[Bruce Byerly]

That’s not how it works normally.  All kinds of places to bypass I suppose. Is the accumulator nitrogen charge flat as well?

[lesnagy]

Well, they say if it won't hold the pressure after pumping up then there is a leak somewhere.  However, if you don't have fluid leaking out and the flaps will go up and down then I'm not sure I'd worry about it too much.  Mine does same thing but hasn't been much of an issue. 

Just my 2 cents,

Glenn

thats what I was thinking as well. thx Glenn

[lesnagy]

That’s not how it works normally.  All kinds of places to bypass I suppose. Is the accumulator nitrogen charge flat as well?

Ah good question. I will have to check the accumulator pressure to verify.

[ghancock]

Just curious Bruce,  Would a low nitrogen charge make it fluctuate?

Thanks,

Glenn

[Bruce Byerly]

Just curious Bruce,  Would a low nitrogen charge make it fluctuate?

Thanks,

Glenn

Glenn, I would need to consult my guys for a real answer and to freshen up my system knowledge (recurrent?) but I think the system tends to bang as there is no “cushion” of nitrogen. If it’s bypassing and the charge is flat it will rapidly cycle on the aux pump for sure.  I have no scientific data but I kinda cringe when I feel the hydraulics banging in a plane.  I would think it would be really critical with the 3,000 psi as that kind of pressure off and on would be hard on everything.  Flat accumulators are indicative of a poorly maintained system in my experience.  How often is it checked if there isn’t a trained Commander mechanic looking at it? Answer: Never!

[ghancock]

Ah, I'm sorry, I had my brain set on the aux pump and nitrogen charge.  You're talking about the accumulator system itself and its charge, not  the assist.  I still didn't realize a low charge there would cause the aux pump to go on and off and lose pressure but could be.  I'll check mine and see as I have no other visible leaks at the moment in my system. 

That was recently charged and checked at last annual so hopefully it is still good.

Glenn

[Bruce Byerly]

Yes. The main gear side nitrogen you’ll probably never notice until the hyd fail and you need that system pressure.  I’ve seen broken guages there that might lead one to believe its ok. The one I just picked up won’t hold an accumulator charge very well so it’s going to get rebuilt. Who knows how long that’s been going on.