A multi-mode pressure relief valve, comprising: a body having a fluid inlet port and a fluid outlet port defining a fluid chamber therebetween, the body including a seat at the fluid chamber between the inlet port and the outlet port, the body further having a compressed gas inlet port and defining a compressed gas chamber in flow communication with the compressed gas inlet port, the compressed gas chamber and the fluid chamber being isolated from one another; a piston disposed in the compressed gas chamber, the piston configured for reciprocating movement in the compressed gas chamber, the piston having a spring receiving region; a valve stem, the valve stem movable within the fluid chamber between an open condition in which flow communication is established between the inlet port and the outlet port and a closed position in which flow communication is isolated between the inlet port and the outlet port, the valve stem having a spring receiving region; and a spring disposed between the valve stem and the piston, the spring urging the piston into the compressed gas chamber and urging the valve stem into the fluid chamber to the closed position, the body defining a space between the piston and the valve stem, the spring being disposed at least in part in the space, and the space being open to the environs, wherein the valve is operable in at least three modes, an operating mode in which the valve stem is in the open condition, the valve stem is spaced from the piston, and the piston applies a pressure on the valve stem, through the spring, the pressure being balanced by a fluid pressure of fluid entering the inlet exerting a force on the valve stem, a zero-state mode in which the valve stem is in the open condition, the valve stem is spaced from the piston, the spring is in a relaxed state, and the piston applies no pressure on the valve stem, and a relief mode in which the valve stem is in the open condition, the valve stem contacts the piston and the spring is in a compressed state due to the fluid pressure of fluid entering the inlet exerting a force on the valve stem. a body having a fluid inlet port and a fluid outlet port defining a fluid chamber therebetween, the body including a seat at the fluid chamber between the inlet port and the outlet port, the body further having a compressed gas inlet port and defining a compressed gas chamber in flow communication with the compressed gas inlet port, the compressed gas chamber and the fluid chamber being isolated from one another; a piston disposed in the compressed gas chamber, the piston configured for reciprocating movement in the compressed gas chamber, the piston having a spring receiving region; a valve stem, the valve stem movable within the fluid chamber between an open condition in which flow communication is established between the inlet port and the outlet port and a closed position in which flow communication is isolated between the inlet port and the outlet port, the valve stem having a spring receiving region; and a spring disposed between the valve stem and the piston, the spring urging the piston into the compressed gas chamber and urging the valve stem into the fluid chamber to the closed position, the body defining a space between the piston and the valve stem, the spring being disposed at least in part in the space, and the space being open to the environs, wherein the valve is operable in at least three modes, an operating mode in which the valve stem is in the open condition, the valve stem is spaced from the piston, and the piston applies a pressure on the valve stem, through the spring, the pressure being balanced by a fluid pressure of fluid entering the inlet exerting a force on the valve stem, a zero-state mode in which the valve stem is in the open condition, the valve stem is spaced from the piston, the spring is in a relaxed state, and the piston applies no pressure on the valve stem, and a relief mode in which the valve stem is in the open condition, the valve stem contacts the piston and the spring is in a compressed state due to the fluid pressure of fluid entering the inlet exerting a force on the valve stem.