Randall Young writes:
>> The parts list came from these sites recently posted
>> http://www.briggs-racing.com/tech/leakd.htm or
>> http://members.tripod.com/~Wrenchbender/leakdown.html
>
> Hey, Cool ! Thanks, Rob. I've been wanting to build one for some time, but
> didn't know how big to make the orifice. I've got all the other parts lying
> around my garage, including a spark plug hose and adapter from my
> compression gage.
I think part of the need for an orifice is dependent upon the type of
regulator used. In the commercial ones I've used in the past, what
accomplished the purpose of a graded orifice was either a regulator with a
ten-turn valve, or a ten-turn metering valve after the regulator. Despite
the additional cost, being able to adjust the airflow is more precise (as
opposed to using a fixed orifice). That is how one is able to determine the
rate of leakage as a percentage of the air source. If the leakage rate is
unspeakably bad, a graded orifice will not give as accurate an indication of
that as will an adjustable metering valve.
That said, I suspect the feature is helpful for people running commercial
shops (i.e., one can write on the work order, "65% leakage rate through
exhaust valves," and have repeatable results). For home use, a graded
orifice may be just fine, since the degree of the problem is not as much an
issue as is diagnosis of the problem.
Cheers.
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