I've got 750 hrs on my 360 and rebuild a cylinder (1 of 6) or more every annual.  I was thinking this pump chirp discussion through and am considering installing an accumulator. 

My reasoning is as follows.  I believe that the total of 6 cylinders have a combined leak affect that is not reducable to zero.  Rebuild all 6 cylinders, replace the valve and two cylinders.  You name it, there is still some minor amount of fluid always getting around those O rings.  We mask this reality based on the following.

When we first fill our hyd systems there is air in them.  Try as I did to purge the system,  I think that some air remains initially.  This air is acting as an internal accumulator.  As up hyd pressure reaches 1200psi, the air volume is compressing.  As the slow leak through one or more seals drains fluid and resultant pressure, the air expands maintaining system pressure.  Thus, when we first rebuild a cylinder and add a little air to the system, we fly along fat dumb and happy that we've "solved" the problem when in reality we just recharged our accumulator (air in system).

However, over the course of many gear cycles, air tends to work it's way back to the resevoir resulting in less accumulator affect (and less air friction and damage to the seals).  This reveals itself as more frequent pump chirps.  The operator therefore assumes he has "developed a leak" when in reality the system total leak has not changed.

Parker Hannifan has a great read on picking an accumulator:

http://www.parker.com/ACCUMULATOR/CAT/ENGLISH/MAKINGCHOICES.PDF

I'd appreciate a sanity check before I buy.

Larry,

 

Are you loco?  OK, maybe I jumped the gun................

 

Yes, the 40 liter one looks perfect.  You must let us know how it works(especially if you use it to move the CG forward).  Of course, you must tell us which side (up or down) you choose to place it on...............

 

Page 6 of the accumulator pdf outlines failure modes for which such devices are useful - our simple system doesn't fit any of them as the dump valve, gravity and a few springs solve the most serious problem - failure to extend and lock. 

 

I disagree with the way you have characterized air as both a good and bad component of "system leak".  However, leaks there may be.  You could test your theory by introducing air, hither and yon, by cracking a few fittings and letting some (or a lot) into actuators. Then, see if the system appears "sealed."

 

Internally the system relies on 6 piston o-rings and at least three more in the pump, not to mention the actual operational position of the shuttle valve and the dump valve (it is not worth talking about leaks to the outside - shaft and actuator end seals - they must be fixed immediately).  The most common cause of internal leaks are scratches on the surfaces where the o-rings must seal or o-ring failures.  These are frequently precipitated by dirt in the system, sometimes present because of building techniques, assembly faults as the crucial o-rings have to pass some ugly cuts (ports) in the cylinders during assembly and cylinder scratches also introduced by assembly.  Also, not all the fluid leaves the actuator as there is space at either end and a rebuild will frequently find o-ring residue (darkening the fluid) in each end at disassembly.  Some leaks only occur (show up) at the end of a stroke, but not on both sides of the system. 

 

Right now I have a 20-second cycle blip on the down side and none apparently on the up side - it has been that way for 18 months.  I, too, have grown weary of replacing/rebuilding actuators, etc.  I see red when I think of the system.  It will have to break a lot worse than it is now for me to start debugging.

 

If you have actual serious leaks, the accumulator will not help.  If your air concept is correct and internal system leak occurs, you would need a very large reservoir as the accumulator slowly pushes fluid to the other side.  You cannot use two accumulators because the pressure requirement is different on each side and if passage of the fluid built up too much pressure on the other side, the pressure switch would not allow the pump to operate.  So there.

 

OK, go ahead, use two 40 liter accumulators.  There is plenty of space in the area described as the "co-pilot seat."

 

Grayhawk

 

PS: Weld the gear down and use wheel pants.  See Mr. Hammer.