Source of green donuts for instrument tubing installation?

Available from Farm Supply stores, veterinarians, Tractor Supply stores.
Note: I use them, but out here in the high desert, where double-digit humidity is the exception, not the norm, the rubber donuts dry out and crack after a few months. But then, considering their intended purpose, longevity is not a part of the design.

On Friday, April 6, 2018 at 12:02:45 PM UTC-7, wrote:
Available from Farm Supply stores, veterinarians, Tractor Supply stores.
Note: I use them, but out here in the high desert, where double-digit humidity is the exception, not the norm, the rubber donuts dry out and crack after a few months.

Fuel injector O-rings might work; they tend towards large cross-sections and small IDs.

I dont use the docking rings anynore, after a few years they deteriorate to mush. I now use a short length
of silicon tube that fits over the instrument tube, a much better lasting material, and cheap.
Dave

On Friday, April 6, 2018 at 4:55:52 PM UTC-7, wrote:
I dont use the docking rings anynore, after a few years they deteriorate to mush. I now use a short length
of silicon tube that fits over the instrument tube, a much better lasting material, and cheap.
Dave

Silicone is a good choice. If you prefer O-rings, though you cannot always go by color, green ones are used in auto air conditioning system seals and indicate HNBR. This would be a particularly good rubber for glider tubing "clamps" as well. See the link for HNBR characteristics:

http://www.mantaline.com/capabilitie...e/hnbr-rubber/

bumper

Is there a particular reason to use donuts or anything similar at all for instrument installation? Just push the tube to pneumatic port and go flying.

Using them prevents leaks later on, clamping the tubes.

On Monday, 9 April 2018 10:05:36 UTC+3, wrote:
Using them prevents leaks later on, clamping the tubes.

I have fixed two leaks in pitot static systems over the years. Both were caused by clamped fitting. That's when I started to take seriously the instruction to never clamp pneumatic tubes with anything. Silicon tubes are idiot-proof, PVC tubes age and may become loose if fitting is connected frequently, the fix is to shorten the tube few centimeters and then plug it back.

On Monday, April 9, 2018 at 3:05:36 AM UTC-4, wrote:
Using them prevents leaks later on, clamping the tubes.

Has anyone ever tried a short piece of shrink-sleeve - no longer than the barbed fitting on the instrument - over the tubing? Slip it into place and hit it with a hot-air gun. Should shrink uniformly before doing damage to the tubing.
Uli
'AS'