It seems that my January article “What does a “suitable telltale indicator” look like when we have a dual relief system” was a hit as I received numerous requests for information on how to get these special gauges. And as I promised each of you in the ammonia refrigeration industry, here is what I have used on my NH3 refrigeration RV systems:
The gauge on the left (with the red-colored face) is a different style of tell-tale indicator made by one of the largest and best ammonia refrigeration equipment companies. The drawing image on the right is another style from the same manufacturer and is very similar to the one I provided in the first article. Now, this is NOT a formal endorsement as I know how refrigeration personnel has their preferences when it comes to their equipment favorites, but this manufacturer has offered these devices for quite a while and they are field-tested and proven (IMPO). And I like this manufacturer, as they are upfront in stating their equipment limitations per their design:
rupture disc assemblies (RDAs) are used to indicate which pressure-relief valve has discharged. A pressure-relief valve will re-seat after discharging. However, a rupture disc remains open after bursting. (A rupture disc is not a stand-alone safety device.) An installed pressure gauge or switch (required by code) provides a visual indication that the rupture disc has burst. Also, rupture disc assemblies provide a hermetic seal to help eliminate any possibility of minute losses of refrigerant via pressure-relief valve seat materials.
For those interested, here are some more pics and order information from this manufacturer: