On May 23, 8:07 pm, Marc Ramsey wrote:
Darryl Ramm wrote:
I always put a tape over the probe port when not in use to keep dust
out.

In my opinion, this requires a disclaimer. Nothing would ever happen to
Darryl's instruments, of course, but for the rest of us, if one has
expensive mechanical varios, one would be ill-advised to place tape or
any other airtight seals on the probe port. I don't think we need
another long thread on whether or why this is a problem, but based on
first-hand (expensive) experience, don't do it. I keep a collection of
vinyl caps (available from McMaster-Carr or any large hardware store)
that fit the probe port, each with a tiny hole in the center that I made
with a heated needle...

Marc

Marc

Lets make it a concise short thread then. You got me - I'm not sure
how this would hurt a vane style (winter) vario or even a Sage vario
since all ports of the triple probe mechanism will be at the same
pressure and may all be increasing or decreasing in pressure (but at
the same pressure) due to temperature changes or altitude (towing
glider in the trailer). So what exactly causes the failure?

If you have separate TE/pitot etc. tail probes, or instruments cross
configured to say use the triple probe TE line but fuselage static
sources etc., then taping over a port I could see might cause damage -
but 1. that's not what was being discussed and 2. I'd also consider
cross configured pneumatic systems misconfigured. Single port devices
like the Altimeter should not be on the triple probe static port. I'd
be surprised if absolute pressure transducer electronic compensated
varios would have such little headroom they could be damage by this.

Still I'll give you that those plastic cups better than tape just
becasue they don't leave gummy residue and probably less prone to
falling off than a piece of tape.

Darryl