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. 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 below is a different style of tell-tale indicator made by one of the largest and best ammonia refrigeration equipment companies. Now, this is NOT a formal endorsement, as I know how refrigeration personnel have their preferences regarding their equipment favorites. Still, this manufacturer has offered these devices for quite a while, and they have been 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:
Parts and Bulletins to order and better understand these devices from Hansen.