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

Single hose attached to a single nurse tank unit with a 350-400 psi/NH3 rated hydrostat highlighted.

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.