Gas powered fluid pump with exhaust assist valve

A method for pumping a liquid comprising the steps of:

• coupling a tank to a liquid source and a liquid outlet via check valves openable by positive pressure differentials from the source to the outlet such that liquid flows into the tank absent pressure in the tank, the tank also having a gas inlet port and a gas exhaust port;
• coupling a supply of pressurized steam to the gas inlet port by opening an associated gas inlet valve at the gas inlet port and closing a gas exhaust valve associated with the gas exhaust port, thereby pressurizing the tank to a pumping pressure and forcing the liquid through the liquid outlet;
• closing the gas inlet valve and opening the gas exhaust valve, whereupon pressure in the tank falls;
• and,
• opening an auxiliary gas exhaust valve at a pressure below the pumping pressure, for assisting in reducing pressure in the tank below a pressure obtained through the gas exhaust valve and the gas exhaust port.

A steam pressure driven fluid pump comprising:

• a pump tank having a liquid inlet with a check valve and a liquid outlet with a check valve, said check valves permitting flow only in a positive pumping direction from the liquid inlet into the pump tank and from the pump tank to the liquid outlet, the pump tank also having a steam inlet port coupleable to a pressurized steam supply for pressurizing the pump tank, and a steam exhaust port for venting pressure in the pump tank;
• a pressure inlet valve for the steam inlet port, a pressure exhaust valve for the steam exhaust port, and a mechanism operable alternately to close the pressure inlet valve while opening the pressure exhaust valve, whereupon pressure in the tank is vented and liquid can flow into the tank through the inlet check valve, and then to open the pressure inlet valve while closing the pressure exhaust valve, whereupon pressure increases in the tank to a pressure level sufficient for urging the liquid to flow through the liquid outlet;
• and,
• an auxiliary pressure exhaust valve coupled to the tank and having a valve body biased inwardly of the tank, the auxiliary pressure exhaust valve opening inwardly when the tank pressure falls below a predetermined threshold level,
• such that during liquid filling operation, the pressure exhaust valve opens, reducing tank pressure below the predetermined threshold level, whereupon the auxiliary pressure exhaust valve also opens to facilitate venting additional steam pressure generated when the liquid entering the tank is heated to boiling.