I recently purchased a new pressure/temp guage for my boiler, and upon removing the old one, noticed that it had an adapter fitting which changed the thread sizing, but also had a spring and a rubber cap on it, which appears to have something to do with the pressure portion of the guage. My new guage did not come with this "adapter fitting" Do I need this piece for the new guage, or simply get a reducer coupling and install it?

 

I'm somewhat mystified - maybe others will weigh in.

What you are describing is a "tridicator" - measures pressure and temp. I think they have either 1/4" or 1/2" threads - 1/2" being more common. They should screw right into a port on the boiler - they are immersed directly in the boiler water (no instrument well). Winters is a popular manufacturer: Pressure Gauges, Temperature Gauge, and Combination Pressure Temperature Gauges for Radiant Heat and Hydronic Heating Applications

The spring and rubber cap seem strange to me. Posting photos might help.

An aside: tri means three, right? Then why is a gauge that measures two variables (pressure and temperature) called a tridicator?

 

Pictures by cheinemann_605 - Photobucket

The first 8 photos in album have pics, and descriptions.
One more question I have about this as well. If you look in the pics, at the far left, you can see a pipe "T", where the front fitting is open. This is where the guage threads in. Could I add a pipe nipple to extend the guage out further to be more visible?

 

Probably not without reducing the temp readings a bit. Otherwise, Yes, if everything fits.

 

yes, but when comparing the fittings, do I need to get the adapter fitting as pictured on the old guage?

 

The 'check valve' on the immersion well is there so that you can remove and change the gauge without having to drain the boiler. When you screw the gauge in, it opens the check valve so that the gauge can read pressure. If you look carefully at those gauges you will see that around the temp sensing bulb is an annular opening. This is the opening for the pressure gauge section.

With this type of well adapter, you wouldn't want to leave the pressure on the system when you change it though... you would still want to drop the system pressure to zero, but you wouldn't have to drain the system.

If the new gauge fits in the 'adapter' I would use it. It will have to thread in far enough that you can tighten it so it don't leak, and push the check valve open a bit so the pressure gauge works. If you measure from the tip of the bulb to the end of the threads and both gauges are the same, then use it... if not, you can just thread it in with an adapter bushing and it will work fine, but you will have to drain the boiler when changing the gauge... just like you did this time!

Mike, I think the 'tri' part of tridicator refers to the manually adjustable 'third' needle on the gauge... you know, that needle that is absolutely pointless... well it does have a point, but the silly thing is useless... IMO.

 

very thorough answer! Thank you much! Finally, If I were to use a 3-4" pipe nipple to extend the guage out further, for easier viewing, how much would this affect the temp pressure readings? Or, is this not a recommended practice?

 

Pressure, probably no difference. Not enough difference for any perceptible pressure drop in the connecting pipe.

Temperature, maybe some... I guess it would depend on how much 'stirring' occurs in the nipple. I suppose it could be a noticeable difference. It _might_ eventually reach the correct reading, there might be a bit of 'lag'. The bulb really should be directly in the flow.

 

I was looking at those tridicators to get some instrumentation on my hydronic system. I'm not looking to install them on the boilder, but rather on pipes leading into and out of various manifolds.

Can they be used on a T off a pipe? The stem seems pretty deep, 2.124", would there need to be a nipple off the T to allow enough depth so the bulb fits into the pipe? How far into the flow does the bulb need to extend? Does the bulb provide a significant resistance to water flow? I'd be looking to use these on 1" and 1.25" pipes (either copper or iron).

 

I've been pretty happy with these:

Temperature Gauge, Analog Temperature Gauge for Radiant Heat Systems and Hydronic Heat Applications

The tee fittings can get pricey though for the larger sizes...

The thermometer itself is a 'slip fit' into the well, so you can use 1 or 2 thermometers and move them between multiple wells in seconds.

This digital one is kinda neat too.. and I believe the probes fit in the same well as the analog.

Digital Temperature Gauge, Digital Temperature Gauges for Radiant Heat Systems, Digit-Stat DS-60P for Hydronic Heating Systems

 

The thermometers suggested by Trooper look ideal. But if you want a quick-and-dirty approach, you could consider strap-on thermometers, such as: Mr. PEX MP748 - Mr. PEX - Strap on pipe Thermometer (70-200F) (1/2"-4" Pipe)

They are fine for metalic pipe, although there will a bit of a temp offset due to the drop through the pipe wall - even though the sensor is in physical contact with the pipe o.d. But, if you are looking for relative temp comparisons between loops, etc., they work - and no plumbing is required.

The brand is "Mr. PEX," but I don't think they would work all that well with PEX tubing.