1. A liquid metering valve operated by pressure reductions, said valve comprising: a cylindrical chamber having a predetermined diameter dimension and connected to continuously and freely receive a supply of said liquid through an upper port, said chamber having a valve seat formed therewithin about a lower port, and a free body disposed within the chamber, said free body having a predetermined specific gravity and predetermined diametral dimensions substantially equal to the predetermined diameter dimension of said chamber to substantially limit the upward floating movement of the free body within the liquid in the chamber to a limited predetermined rate, a stop means disposed to limit said upward floating movement at a predetermined location thus defining a predetermined quantity of said liquid substantially confined between the free body, the cylindrical chamber walls and the lower port when the free body is at its uppermost location, said free body also being adapted to move downwardly while also preventing substantial fluid flow therearound because of the substantially equal free body and chamber dimensions thus forcing said predetermined quantity of liquid from the lower port when the fluid pressure is lowered thereat and said free body also being adapted to cooperate with said valve seat when in its lowermost position and thus positively preventing further liquid from leaving said lower port until the fluid pressure at said lower port has been thereafter raised thus permitting the free body to float upwardly within the chamber but only at said limited predetermined rate to recondition the valve for another operation after a predetermined elapsed time.

9. A metering apparatus for metering a predetermined quantity of liquid into a receiVing chamber when the pressure therein is first reduced but which valve will not again furnish such liquid on subsequent reductions of the pressure in the receiving chamber until a predetermined time has elapsed after the first such pressure reduction, said metering apparatus comprising: a supply chamber for holding a supply of said liquid, a cylindrical metering chamber having a predetermined diameter dimension and connected for continuous and free flowing fluid communication with said supply chamber for holding said predetermined quantity of liquid and for discharging same through an outlet, a floatable body of predetermined diametral dimensions substantially equal to the predetermined diameter dimension of said chamber and disposed within said metering chamber to limit the controlled passage of said fluid with respect to said floatable body and to permit only controlled upward movements at a limited predetermined rate of the floatable body with respect to said metering chamber, a stop disposed to limit the upward movement of said floatable body, a valve seat disposed at said outlet of said metering chamber and adapted to cooperate and seal with said floatable body when it is in its lowermost position thereby preventing further liquid flow from said outlet, and a pressure actuated valve operatively disposed between the outlet of the metering chamber and the receiving chamber whereby the outlet and the receiving chamber are placed in fluid communication upon the first pressure reduction in the receiving chamber thereby drawing the predetermined quantity of liquid from below the floatable body until the floatable body cooperates with said valve seat to prevent further withdrawal, said floatable body having predetermined characteristics including its said dimensions relative to the chamber diameter to prevent its subsequent upward movement and consequent refilling of the metering chamber until a predetermined time has elapsed after the last pressure reduction in the receiving chamber.

14. In combination with a reciprocating piston pump comprising a piston and a chamber within which the piston is reciprocatably positioned for drawing a first liquid into the chamber and for subsequently forcing the first liquid out of the chamber, a one-shot metering valvae means for discharging a predetermined quantity of a second liquid into the said chamber during the first reciprocation of the pump and for preventing any further such discharge until the pump has been quiescent for a predetermined time period.

15. A liquid metering valve operated by pressure reductions, said valve comprising: a chamber adapted to receive a supply of said liquid through an upper port, said chamber having a valve seat formed therewithin about a lower port, a free body disposed within the chamber, said free body having a predetermined specific gravity and dimensions to permit a predetermined rate of upward floating movement within the liquid in the chamber, a stop means disposed to limit said upward floating movement at a predetermined location thus defining a predetermined quantity of said liquid between the free body and the lower port when the free body is at its uppermost location, said free body also being adapted to move downwardly thus forcing said predetermined quantity of liquid from the lower port when the fluid pressure is lowered thereat and to cooperate with said valve seat when in its lowermost position thus preventing further liquid from leaving said lower port until the fluid pressure at said lower port has been thereafter raised thus permitting the free body to float upwardly within the chamber to recondition the valve for another operation after a predetermined elapsed time, and a diaphragm operated discharge valve connected to said lower port for positively opening said lower port in response to a reduction in fluid pressure thereabout, said diaphragm operated discharge valve comprising: a diaphragm, a valve stem mounted for movement upon said diaphragm, and a discharge valve seat, said valve stem having sealing means for cooperation with said discharge valve seat to prevent the discharge of said liquid when the diaphragm is in a first unactuated position and to permit the discharge of said liquid when the diaphragm is in a second actuated position, and one surface of said diaphragm being exposed to the ambient fluid pressure thereabout while the other surface of said diaphragm is maintained at the pressure existing at said lower port.

18. A metering apparatus for metering a predetermined quantity of liquid into a receiving chamber when the pressure therein is first reduced but which valve will not again furnish such liquid on subsequent reductions of the pressure in the receiving chamber until a predetermined time has elapsed after the first such pressure reduction, said metering apparatus comprising: a supply chamber for holding a supply of said liquid, a metering chamber in fluid communication with said supply chamber for holding said predetermined quantity of liquid and for discharging same through an outlet, a floatable body disposed within said metering chamber and arranged to permit the controlled passage of said fluid with respect to said floatable body and to permit upward and downward movements of the floatable body with respect to said metering chamber, a stop disposed to limit the upward movement of said floatable body, a valve seat disposed at said outlet of said metering chamber and adapted to cooperate and seal with said floatable body when it is in its lowermost position thereby preventing further liquid flow from said outlet, and a pressure actuated valve operatively disposed between the outlet of the metering chamber and the receiving chamber whereby the outlet and the receiving chamber are placed in fluid communication upon the first pressure reduction in the receiving chamber thereby drawing the predetermined quantity of liquid from below the floatable body until the floatable body cooperates with said valve seat to prevent further withdrawal, said floatable body having predetermined characteristics to prevent its subsequent upward movement and consequent refilling of the metering chamber until a predetermined time has elapsed after the last pressure reduction in the receiving chamber, and wherein said supply chamber is located within the pisTon of a reciprocatable piston pump.

19. A metering apparatus for metering a predetermined quantity of liquid into a receiving chamber when the pressure therein is first reduced but which valve will not again furnish such liquid on subsequent reductions of the pressure in the receiving chamber until a predetermined time has elapsed after the first such pressure reduction, said metering apparatus comprising: a supply chamber for holding a supply of said liquid, a metering chamber in fluid communication with said supply chamber for holding said predetermined quantity of liquid and for discharging same through an outlet, a floatable body disposed within said metering chamber and arranged to permit the controlled passage of said fluid with respect to said floatable body and to permit upward and downward movements of the floatable body with respect to said metering chamber, a stop disposed to limit the upward movement of said floatable body, a valve seat disposed at said outlet of said metering chamber and adapted to cooperate and seal with said floatable body when it is in its lowermost position thereby preventing further liquid flow from said outlet, and a pressure actuated valve operatively disposed between the outlet of the metering chamber and the receiving chamber whereby the outlet and the receiving chamber are placed in fluid communication upon the first pressure reduction in the receiving chamber thereby drawing the predetermined quantity of liquid from below the floatable body until the floatable body cooperates with said valve seat to prevent further withdrawal, said floatable body having predetermined characteristics to prevent its subsequent upward movement and consequent refilling of the metering chamber until a predetermined time has elapsed after the last pressure reduction in the receiving chamber, and wherein said pressure actuated valve comprises a diaphragm operated discharge valve for positively opening and closing a fluid passage between said metering chamber and said receiving chamber in response to ambient pressure changes in said receiving chamber, said diaphragm operated discharge valve including: a diaphragm, a valve stem mounted for movement with said diaphragm, and a discharge valve seat, said valve stem having sealing means for cooperation with said discharge valve seat to prevent the discharge of liquid when the diaphragm is in a first unactuated position and to permit the discharge of liquid when the diaphragm is in a second actuated position, and one surface of said diaphragm being exposed to the ambient fluid pressure in said receiving chamber while the other surface of said diaphragm is maintained at the fluid pressure existing at the outlet of said metering chamber.