This was posted in another thread, but I thought it would help if it was posted here, too.
On the subject of connecting the Dwyer mano kit tubing to a metal tube probe that can more safely withstand the heat of being inserted into a stove pipe near the stove.
It's better to sleeve the metal tube probe to the mano kit tubing with a larger diameter piece of rubber tubing. That way there is no stretch-stress that will eventually split the smaller size rubber tubing causing an air leak.
Metal tubing is sized by it's outside diameter. Whereas rubber tubing is sized by it's inside diameter. Thus making joining the two very simple by just asking for the same size.
The tubing that comes with the Dwyer mod 25 is slightly larger than 3/16 diameter.
3/16 automotive vacuum line tubing will fit over it perfectly and not leak while also not being overly stretched.
Not all autoparts stores carry 1/8 inch brake line, which would make it easier to slip the Dwyer mano kit tubing over it.
3/16 is a more common size and it works very well, because it is such a common size needed for this application.
1. A 3/16 drill bit, needed for putting the hole for the probe into the stove pipe, is included in most fractional drill bit sets.
2. 3/16 metal tubing fits into 3/16 rubber tubing.
3. That 3/16 vacuum line tubing fits over the 3/16 outside size of the rubber tubing that comes with the mano kit.
So, all you need to remember is, "3/16 inch" when your buying stuff to hook up a Dwyer model 25 mano.
Plumbing and heating supply houses also carry 3/16 copper tubing, which like 3/16 inch brake line, allows a perfect "slip-on" fit with that 3/16 automotive vacuum line tubing.
And because automotive vacuum line is used on engines, it is designed to take higher temperatures that many other types of rubber tubing can't.
The red tubing in the picture is a piece of 3/16 rubber tubing that came with a Dwyer hand-held mano in an oil burner tuneup kit I ought years ago. It is the same size tubing as automotive vacuum line. It fits over the model 25 mano kit tubing with a good leak-proof fit without over-stretching it and risking splitting later on.
FYI - the tubing always gets connected to the right hand fitting on top of the Dwyer model 25,... the "low" fitting. That way the mano will always show negative pressure (pressure drop) within the stove pipe that is caused by stove/chimney system draft. I used a short length of the tubing in the kit to adapt the tiny diameter of the gauge's plastic connection fitting to the 3/16 inch rubber tubing.
The "pig tail" piece of short tubing on the left-hand fitting is there just to cut down on dust getting into the gauge but still allows the gauge to sense room air pressure so it can show the difference between that and inside the stove pipe.