REFLECTOR: Franklin Oil temp and flow data

Thu Nov 21 08:36:52 CST 2013

I came across this explanation of Anti Drain Back Valves in oil filters. It
explains the operation very thoroughly.

http://origin.library.constantcontact.com/download/get/file/1104540460641-12
9/Tempest+OilFilterValves.pdf

Grover McNair

McNair Performance Inc.

6404 Westgate Rd.

Raleigh, NC 27617

919-781-3604

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Laurence Coen
Sent: Thursday, November 14, 2013 2:30 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Franklin Oil temp and flow data

Brian,

There are two valves in the "bypass plate" and they perform independent
functions.  The pressure regulator valve sets the oil pump pressure at
80PSI.  That is the maximum pressure that can exists anywhere in the system
and is also the maximum pressure that the oil cooler can see.  Please note
that this has nothing to do with the external loop bypass valve.  Your data
would indicate that your statement that no oil flowed for nine minutes is
incorrect.  I don't how you are measuring oil flow or where but the fact
that there is a differential pressure at the output of the oil cooler and
the galley is only possible if there is flow through the cooler.  In a
hydrostatic system (no flow) where two points are connected the pressure
will be the same.  Your graph shows a differential pressure at opposite ends
of a tube connecting the oil cooler and the oil galley.  This indicates oil
flow through the cooler from start up to shut down.

Functionally, the Franklin set up works the same as the pressure
regulator/"Vernatherm" in a Lycoming.  In a Lycoming, when the oil is cold,
The Vernatherm opens a bypass on the oil cooler loop.  When the oil gets hot
the Vernatherm closes the bypass forcing the oil to flow through the oil
cooler.  On the Franklin the fact that cold oil is thick when cold causes a
large drop in pressure through the external loop. This in turn opens the
bypass just like the Vernatherm on the Lycoming.  When the oil is hot, the
pressure drop in the external loop decreases allowing the bypass to close,
just like the Vernatherm did in the Lycoming.  In both cases the pressure
regulator simply sets the output pressure of the oil pump.

From: Brian Michalk <mailto:michalk at awpi.com>  

Sent: Monday, November 11, 2013 11:12 AM

To: Velocity Aircraft Owners and Builders list <mailto:reflector at tvbf.org>  

Subject: Re: REFLECTOR: Franklin Oil temp and flow data

>From my notes, and diagrams I made, my understanding of the system is that
the bypass is there to ensure that the cooler is not over pressurized.
There are two regulators.
1) oil bypass, which causes a pressure differential across the cooler.
2) Galley bypass, which prevents overpressure on the engine.

The oil cooler will see an absolute pressure of galley pressure, plus cooler
bypass pressure.  Absolute pressure does not imply oil flow.  Only delta
pressure across the ports to the cooler makes oil flow, and that's provided
by the bypass.

If one looks at the bypass plate, you can see two spring loaded valves.

*    Increasing spring stiffness on the left valve sets the bypass pressure
(delta pressure oil cooler) higher.
*    Increasing spring stiffness on the right side sets the max galley
pressure higher.

The oil pump is a constant volume pump, not constant pressure.  These valves
are "relief" valves, meaning that above a set point, they will allow oil to
bypass the circuit.  If the oil pressure is below the set point, then no oil
is bypassed.  In other words, cranking up the spring pressure does not
necessarily mean you get higher oil pressure.  If the pump is only making
50PSI, setting the bypass at 80PSI is not going to get you more pressure.

That said, I do not know if the cooler bypass is bypassing.  If it is, then
adding a stiffer spring there will cause more oil to flow to the cooler.

On 11/11/2013 9:57 AM, Grover McNair wrote:

Has anyone ever just bypassed the oil bypass valve to allow oil to flow to
the cooler constantly? I realize it would take longer to warm and could
potentially cause temps to be too low.

Just curious.

Grover McNair

McNair Performance Inc.

6404 Westgate Rd.

Raleigh, NC 27617

919-781-3604

From: reflector-bounces at tvbf.org <mailto:reflector-bounces at tvbf.org>
[mailto:reflector-bounces at tvbf.org] On Behalf Of John Dibble
Sent: Monday, November 11, 2013 8:46 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Franklin Oil temp and flow data

On 11/10/2013 8:19 PM, Brian Michalk wrote:

It was about 70F today, not that cold.  The oil flow is just very strange.
It didn't start flowing until nine minutes into the flight, and I don't
think it's a sensor problem because the coolant temp leveled off after it
started flowing.  If this data is correct, I'm not getting enough oil
through my cooler.  The specs on the cooler are for 7gpm, and I'm barely
half there.  Yes, I'm having high oil temp problems.

After my engine rebuild, my oil now takes 10 minutes to warm up.  It used to
take 4-6 minutes.  The reason for so much time is because when the oil is
cool, there is a high pressure drop across the filter/cooler and nearly all
the oil bypasses until the oil in the sump, which warms faster, gets warm
enough to reduce the pressure drop.  The reason mine took less time before
is because the bypass spring was the wrong one.  It was the same as the oil
pressure regulating spring, which means there would be 80 psi across the
filter/cooler, before it would bypass.  That means the pressure off the pump
could get as high as 160 psig.  YIKES, but it ran without incident for 1100
hours.  I couldn't get one of the special bypass springs for the Franklin,
so I made my own from a spring from the hardware store that I calculated
would give 20 psi pressure.  My oil runs 10 C cooler after the rebuild and I
attribute most of that to new bearings.  New bearings have a smaller space
between the bearing and crankshaft, so less oil passes through and therefore
doesn't pick up as much heat.  That reduces the oil cooling requirement.
Also, with more oil now bypassing the cooler, there is less oil to cool and
that contributes to a lower oil temp (leaving the cooler) as well.  I should
point out that I have a larger oil cooler than the standard.  My CHTs are 10
C lower as well and I attribute that to the lower oil temp.  My oil pressure
runs 10 psig higher, also due to the lower oil temp.  One trick I use to
warm the oil with less idling is to runs for 2 minutes, then shut down for
10-15 minutes.  When I start back up, the oil warms up in 2 minutes.  This
way my CHTs are still low.

John

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