46 CFR §95.16-25

1. (a)A check valve must be provided between each cylinder and manifold or distribution piping. The valve must be permanently marked to indicate the direction of flow.
2. (b)If the same cylinder is used to protect more than one space, normally, closed stop valves must be provided to direct the agent into each protected space.
3. (c)Each cylinder must be fabricated, tested, and marked in accordance with 46 CFR 147.60(b) and 49 CFR part 180.
4. (d)The cylinders in a common manifold must be:
   1. (1)Of the same size;
   2. (2)Filled with the same amount of agent; and
   3. (3)Pressurized to the same working pressure.