350-400 psi/NH3 rated hydrostatic relief valves (Hydrostats) are required to protect PERMANENTLY assigned and attached hosing lines between shut-off valves in the following locations:
1. Single Nurse Tank Unit with Single Hose/Line
2. Dual Nurse Tank Unit
- Single hose/line: In nurse tank withdrawal valve.
- Merged hoses/lines: In one nurse tank withdrawal valve provided that the only other shut-off valve is located at the opposite end/hose connection points.
- Crossover hose/line: In nurse tank liquid fill, vapor, or between other pairs of shut-off valves.
3. Application/Toolbar Unit
- The area that includes the withdrawal hose to the discharge side (female side) of the break-away coupling device.
4. Other Locations
- Permanently attached/assigned hose/line in which liquid ammonia can be isolated between shut-off valves.
Though not required, a hydrostat installed in nurse tank withdrawal valves and connections provides an added layer of protection for TEMPORARY assigned/attached hosing/lines.