I need to insert a temperature probe into my pool piping. I am on the pressure side of the filter, so around 10-20 psi typically. My initial idea was to use a screw in plug in the existing 1/2" NPT side inlet tee, drill a hole and epoxy the probe in place. Assuming that worked, it would make it difficult to replace or inspect the probe. Also, the probe is 5mm diameter teflon, so gluing is challenging, requiring specialty adhesives that have no data about full-time submersion or resistance to swimming pool chemistry.
I know sticking probes into pipes is a pretty common requirement, so there must be existing solutions, but I don't know the name of the correct fitting. The closest thing I can find is a cable gland with NPT threads, and while I can find them rated IP68 (dustproof and waterproof to 3+ m) and 10 bar (145psi), I don't know if this is their intended use, i.e. permanent submersion and preventing water intrusion from what would normally be the "dry" side (the inside of an electrical enclosure). I'm fairly certain this would probably work, but I'd rather have a bit more confidence, and, if possible, use the correct fitting for the job.
My electrics are all in a NEMA rated outdoor enclosure with proper waterproof glands located several feet above the temperature probe, so I'm not concerned from that aspect. I just don't want a slow leak that gradually drains the pool.
Best Answer
The usual way is to use a T with the middle outlet being vertical:
With a proper fitting, you screw this hollow adapter in. Ecnerwal says in a comment it is called a "thermowell".
Fill this with mineral oil and dip your temperature probe in.
The oil transmits temperature, but the probe is not submerged in water, nor under pressure, so it can be inspected and changed.