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All the mechanical temp gauges I have ever seen
worked by measuring the change in pressure of a fluid that is in a bulb of some
type. Altitude has nothing to do with it since it is a closed system. They are
actually a pressure gauge with the change in pressure correlated to temperature
of the fluid in the bulb VS a spring. It works just like a mercury thermometer.
I don't like mechanical pressure gauges for engine
fluids because most of them use crappy nylon line with brass compression
fittings. I have had these fail and spray oil all over hot headers. Not good. So
if you use one make sure to replace the cheap nylon line with AN
hardware. Mechanical gauges introduce another mission critical point
of failure. I have also had the gauges start leaking oil. These were high
quality automotive racing type gauges.
The nice thing about electrical sending units is
when they fail the sender is still a pipe plug. It's also a lot easier to run
signal wire, than plumbing, or thread the big bulb of a temp sender through the
firewall. In addition the wire is still useable without ripping it out even if
you go with a new gauge and sender. This is not true with a capillary and bulb
system. You have to rip it all out and thread the new one in. Plus the capillary
tube is usually way too long and you can't cut it.
Monty
----- Original Message -----
Sent: Friday, January 15, 2010 7:09
PM
Subject: [FlyRotary] Re: Mechanical
gauges
Perhaps nothing… I don’t have a
clue as to how they would work. Looks like it would be either pressure…
or fluid running in a circuit. If it is pressure, how would it adjust to
changes in altitude? If fluid, then how could you calibrate for the loss
of temp between the engine and gage? I like the electrical ones…at least
I have a vague notion of how it works…
:>)
Bill
B
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of ben haas
Sent: Friday, January 15, 2010 3:28
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Mechanical
gauges
What is wrong with a mechanical
temp gauge that uses a capillary tube for a sender?
Ben
Haas
www.haaspowerair.com
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