Jerguson

Jerguson – now part of Clark-Reliance Corporation – was introduced to the Norwegian offshore and onshore market by American oil companies that were in the establishment phase on the Norwegian shelf in the 60s.
Over these 50 years, the products have been in operation on most installations in Norway, and are increasingly used in the petrochemical industry.
Jerguson has a significant product range that includes level glass for 690 bar with temperatures up to 316 C. The products meet the requirements of Norsok I-001 rev4 and Equinor TR3032.
The level glasses can be supplied in most machinable materials in accordance with Norsok M-650.
Through the level glass, or sight glass if you will, you can visually see what liquid level you have in your tank.
In many contexts, it is also used as a reference instrument for the other level measurements on the tank.   New design of “safety ball check valve” for Jerguson sight glass for level measurement that makes it easy to see if the valve is open or not and the possibility to lock the valve.
See video safety ball check valve (with sound).
Possibly.
image and more info: https://www.hi-as.no/safety_ball_check_valve_jerguson/ Level glass / sight glass for measuring the volume of liquid in tanks, also for high pressures and/or temperatures.