Fast acting shuttle spool valve

A spool valve for controlling the flow of a gas into a reciprocating piston cylinder, comprising:

• an outer casing;
• a spool slideably inserted into the casing, the spool valve having a first and a second non-waisted end portions and having a waisted middle portion;
• an intake port for fluids entering the casing;
• an output port for fluids exiting the casing;
• wherein a first non-waisted end portion covers the intake port during a first valve-closed event as the spool slides in one direction within the casing to a first position;
• wherein the waisted middle portion is sufficiently wide to uncover both the intake port and the output port during a valve-open event as the spool slides in the one direction within the casing to a second position;
• wherein a second non-waisted end portion covers the output port during s second valve-closed event as the spool slides in the one direction within the casing to a third position;
• wherein the spool is operable to prevent the flow of the fluid into or out of the casing during the first valve-closed event and the second valve closed event;
• a gas actuator operable to both push and pull the spool within the casing, such that a valve-open event and the first and the second valve-closed events occur as the actuator pushes and pulls the spool;
• wherein the gas actuator comprises a chamber within the casing at both ends of the spool and a poppet valve associated with each chamber operable to compress and expand the gas within the chamber.