Hi, the statement quoted below seems to come from a position that I might
have suggested deletion of the strain relief/vibration loop in the oil line
or other application.
I did not make that assertion.
My assertion is that there are more reasons than only strain relief or
vibration tolerance to occasionally employ a loop in a tubing installation.
As far as oil pressure sensing or monitoring in a KR goes:
In my aircraft engine installations I use not just a loop but a coil of 2
turns for strain relief and vibration tolerance in my metal tubing between
the engine and firewall. Also I use steel tubing rather than copper for
greater toughness and resilience as copper makes for a poor performing
spring compared to steel. Also in my KR there are two tubes present with
one for oil pressure sensing and another for fuel primer. These tubes are
1/8" OD and terminated with brazed on brass fittings at the engine end,
flare fittings at the other end.
My 1/8 OD steel tubing is a bit small inside and so seems to make the
primer slow to operate in case you're wondering. The tubing had the
advantage of being on hand. The steel tubing I found was 1/8 OD and has
what most would describe was a "thick wall" profile, leaving a very small
passage inside as I recall. No orifice for this install as the tubing
inner diameter is so small that equivalent function of the orifice is the
tube itself. My co-workers say a tube of this style is a capillary tube.
My KR oil pressure tubing is functionally redundant as it is backed up
using a grand rapids system engine info system in which the tubing
functionality is performed by electrical wires via an electric engine
mounted oil pressure sensor. The grand rapids system provides a single red
warning light for for any engine parameter out of range. So If I am busy
and don't notice the low oil pressure indication on the gauge then the red
light will alert me to "something's wrong".
If I were to do it over I would install an oil pressure gauge and an oil
pressure low warning light controlled by an engine mounted oil pressure
sensing switch.
A "something's wrong" general purpose indicator light turns out to be not
so great a message. Better if the warning light's meaning were more
specific. The grand rapids digital display will automatically pop up the
answer to "where did the alarm come from?" on the digital display, but only
after it deletes all other display data so suddenly you can not see any
other parameter on the display unless you start pushing buttons. Or if set
to multi display you have to start reading the display. Just reading that
display is not as quick and effortless as seeing a simple specific warning
light. Oil pressure sensing is only one of many channels of info in the
grand rapids system and I want to record all that stuff so it has it's
benefits. I am just saying that a more simple and functionally effective
backup to the oil pressure gauge would be a cheap lamp and pressure switch:
a classic idiot light for oil pressure. I am considering removing (in
software) the low oil alarm from the grand rapids display while retaining
the recording functionality and addition of the low oil pressure specific
warning light described above to the instrument panel. With a dedicated
low oil pressure warning light I could relegate the grand rapids unit to
displaying a smaller selection of error conditions, raising the specificity
of the indications.
jg
On Sat, Dec 18, 2021, 07:17 <shafferj45...@twc.com> wrote:
> To KRnet Attn: John Gotschall
>
> To KRnet Attn: John Gotschall
On the rigid installations, that you described, with no vibration,
whatsoever, Consider that all metals expand and contract, via
temperature changes. Engine oiling systems have a rather large
temperature change. You will never see the expansion and contraction
of that little copper tube, but it is happening. This causes " Work
Hardening ", of the copper tube, just as any metal being stressed by
vibration, bending forces, etc. At some point, these stresses will
cause any metal to fail at the point of concentrated stress. The loop
is there to spread out, or minimize, any fatigue of the tube at any
one single point. We all have choices, but why would anyone want to
bet their life on such matters.
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