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Check that the drain-back hose is not restricted/crimped
in some manner as well, Mark.
While blow-by pressure in the crankcase could pressurize
the oil-drain back a few psi and possible cause the seal blow out - a
blocked/restricted drain-back hose will almost certainly cause the seal to blow
out very quickly. So I would also carefully check the drain-back hose/line
for possible blockage or restrictions.
While the oil pressure is nominally down to almost zero at
drain-back, IF the drain back line is restricted/blocked for
some reason, then the oil pressure there can very quickly build up close to
80 psi in the PSRU drain back area.
The reason is that while the oil is flowing normally
through the PSRU then the oil pressure is dropped across the various
restrictions it meets it meets in the gearbox so that is zero by time its ready
to drain back. But, once the oil stops flowing out (due to say a blocked
hose), then there is little/ no pressure drop in the PSRU as the flow
decreases/stops - this means that the pressure of the oil at the drain point
will eventually climb to/near the input oil pressure level of 80
psi.
An electrical analogy is that if you have a resistor and
apply voltage to one end and ground (sink) the other end, you will measure the
applied voltage (oil pressure) on the one end and zero voltage on the grounded
(sink) end. However, if you remove the ground (sink), you will find the
voltage(oil pressure) will measure the same on both sides of the resistor - no
current/oil flow => no voltage/pressure drop.
I personally find it hard to believe that give the oil
pressure could rise to 80 psi at the drain back point that blow-by pressure in
the pan would prevent drain back. But, it could offer enough back pressure
to cause the oil in the drain back area of the PSRU to climb to a pressure level
matching the blow-by pressure - I would think at most 2-3 psi. But, That
may be more than enough - if the seal is not designed to handle it.
Ed
Sent: Sunday, September 19, 2010 9:18 AM
Subject: [FlyRotary] Re: Check PSRU Oil Drain-back hose was Re:
Watch that psru oil seal
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
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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