Mailing List flyrotary@lancaironline.net Message #52150
From: Mark Steitle <msteitle@gmail.com>
Subject: Re: [FlyRotary] Check PSRU Oil Drain-back hose was Re: Watch that psru oil seal
Date: Sun, 19 Sep 2010 08:18:38 -0500
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Ed,

You and Lynn may have hit on something regarding the crankcase vent line being too small.  It may have been marginally acceptable with the side port engine, but way undersized for the fire-breathing p-port.  First time I ran it real hard, out came the seal.  I am using the stock vent line, but will go ahead and up-size it while I'm fixing the psru seal.  

Mark

On Sun, Sep 19, 2010 at 8:10 AM, Ed Anderson <eanderson@carolina.rr.com> wrote:
Mark, here's another thing to check for - the oil drain back hose from the PSRU
 
The PSRU typically has its oil drain-back to the oil pan which can be "pressurized" by blow-by of the rotors.  This back pressure could  impede the flow back of oil from the PSRU because by the time the oil in the PSRU is ready to drain back it has dropped the oil pressure from its 80 psi input to practically zero.  So it basically gravity feed back to the oil pan.   I guess the oil pan pressure could get to the point of serioulsy impeding the oil blow - but I would think that much crank case pressure would have given other indications - such as blowing your dip stick out {:>)
 
Now if the PSRU oil drain-back became plugged/restricted/crimped  for some reason then the pressure on the seal might eventually reach near the 80 psi input mark and that would put considerably force on the seal.  So (as I know you already planned) check out the drain back hose.
 
But, in any case mechanically restraining the seal sounds like a smart ideal in any case
 
Ed
Edward L. Anderson
Anderson Electronic Enterprises LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com

Sent: Sunday, September 19, 2010 8:39 AM
Subject: [FlyRotary] Re: Watch that psru oil seal

Lynn,

  Am I reading you right in saying that it it was crankcase pressure, not oil pressure. And to relieve said pressure, one needs a larger relief tube than the factory one on the oil fill. (call it perhaps 3/16" without going to the hanger and measuring)

Ben

--- On Sun, 9/19/10, Lehanover@aol.com <Lehanover@aol.com> wrote:

From: Lehanover@aol.com <Lehanover@aol.com>
Subject: [FlyRotary] Re: Watch that psru oil seal
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Date: Sunday, September 19, 2010, 7:14 AM

In a message dated 9/19/2010 5:41:35 A.M. Eastern Standard Time, msteitle@gmail.com writes:
Kelly, 

My custom adapter plate was built on a Bridgeport mill.  The hole spacing (and sizes) were obtained from a drawing for the actual RD-2C plate.  Could it be a thou or two oversize?  I guess that's possible, but I don't think so.  The machinist that did the work is very meticulous.  However, before reassembly, I'll definitely check it to be sure.  The bottom line is that there is 90-100 psi trying to push it out of place.  So, I feel that a mechanical fastener is the only real way to guarantee that it stays put 100% of the time.  

Mark
Anything not positively retained in aircraft, will eventually fall off. Garlock style lip seals will just barely hold back oil splash with little to no pressure. You see Garlocks  pressed into cavities that are cast or formed with retaining lips at the end. Not into smooth bores. More than a few pounds against a lip seal over heats the seal and fails the lip allowing a leak. Note the oil drainback paths in the rotary, so seals see no pressure even beside a main bearing other than from crank case gasses..
 
I had a weaver Brothers three section dry sump pump that had the pressure section in the blind end of a casting so no high pressurized oil was exposed to a seal of any kind. The drive shaft extended from the scavenge pump end, so any pressure pulses would of minimal size against the Garlock seal pressed into a smooth bore in the end plate. Each session the seal would be found dancing along the shaft with oil dripping off of everything. A competitor told me to retain the seal with a plate of some kind. Once that very long weekend was over I did that with a plate and three little screws. I replaced the single lip seal with 2 half width lip seals and the plate and never had another problem. I also cut a tiny groove from the suction side of the pump to the center of the shaft cavity. Oil drain-back to a lower pressure area. 
 
Lip seals are the most freedom loving seals of all. If pressurized they turn their lips inside out and leak on you.
 
If you persist, they will escape the bore and dump your oil out on the ground. They have been that way since the first day. Thought should be expended on the release of crank case gasses. The street engine has a tiny tube sticking out of the oil filler neck. This is way too small for operation above about 3500 RPM.
 
Lynn E. Hanover

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