984 K Road
Minden, Nebraska 68959
308/832-22OO
HODGES VOLATILITY TESTER
The most important thing to consider when using auto fuel in aircraft concerns
vapor pressure or volatility. The fact that approved engines operate quite
well on auto fuel is not in dispute. But given the right set of circumstances
any airplane can vapor lock. Until the Hodges tester was developed the only
method of determining a fuel's vapor lock potential was to send a sample
of fuel to a laboratory along with a substantial fee and wait patiently
for six weeks to receive the results. This is of course totally impractical.
Thanks to Dr. Ray Hodges of Australia, a simple fail-safe portable tester
is available. The Hodges Fuel Volatility Tester is small enough to be carried
in the airplane and will tell you at a glance whether or not the fuel has
any serious vapor lock potential, given the current outside air temperature.
It immediately tells you if the fuel could cause vapor lock, regardless
of contributing factors such as, temperature, altitude, seasonal blend,
weathering history, or blends with avgas or ethanol. The operation of the
tester is fail safe since air leaks cause low ("unsafe") readings.
This tester has become standard equipment for many people who use auto fuel
and desire a preflight safety check of the fuel. Operating the tester is
quick and simple. A sample of fuel is drawn into the syringe; the syringe
is then coupled to the gage and the plunger is drawn down. This creates
a vacuum in the syringe, the fuel boils, evaporates, and a reading is obtained
on the gage which indicates whether the fuel is "safe or unsafe".
Complete instructions are, of course, included with the tester.
The Hodges Volatility Tester gives an on-the-spot answer to the question
- "could the fuel cause vapor lock?" - and unlike all other standard
tests it does not give an answer that needs further interpretation. If the
fuel has weathered to a lower Reid Vapor Pressure (RVP) than normal, the
equipment automatically accounts for the current vapor pressure, and registers
a "safe or unsafe" result dependent only on the current value.
This capacity to read current value gives the pilot the option of blending
fuels until a safe reading is obtained, or of delaying the flight until
a cooler part of the day when a "safe" reading can be obtained.
Please note that the volatility tester does not give octane ratings, nor
does it specifically give you RVP. However, a chart is available at your
request that can be used to extrapolate RVP to within 1 psi. RVP by itself
means nothing. The tester is designed to give a "go-no go" indication
which is really the most useful way to evaluate the fuel for vapor lock
potential. Furthermore, samples for testing must be fresh, since any sample
collected in an open jar or blends tested that are not properly mixed won't
give a true result.
Highly recommended for any low wing pump fed airplane, and for all homebuilts,
the Hodges Volatility Tester sells for $65.00 (shipping included).
