Variable volume valve for a combustion powered tool

A variable volume metering chamber and valve assembly for use with a pressurized fluid supply containing a fluid in a combustion-powered tool, said assembly comprising:

• a housing defining a metering chamber having a plurality of ports including an inlet and an outlet;
• a first spring-biased valve disposed in said housing to control fluid flow through said inlet;
• a second spring-biased valve disposed in said housing to control fluid flow through said outlet;
• an actuator assembly, connected to said first and second spring-biased valves and sequentially operable from a first position, in which said first spring-biased valve is open and said second spring-biased valve is closed, to a second position, in which said first and second spring-biased valves are both closed, and a third position, in which said first spring-biased valve is closed and said second spring-biased valve is open;
• said valve assembly being configured and arranged so that a volume of fluid entering said chamber from said inlet in said first position is collected in said metering chamber, sealed within said metering chamber in said second position, and released from said metering chamber in said third position to provide a constant volume of fluid for each sequential movement of said actuator from said first position to said third position;
• and
• a heater provided in operational relationship to said housing for heating said metering chamber.