A four-chamber piston pump has been tested in several evolving configurations. A significant improvement over an earlier hydrazine pump is the elimination of warm gas leakage in the powerhead. This has been achieved through the use of soft seals for the power piston and intake-exhaust valves, with gas temperatures approaching 800 K (980 F). The pumped fluid serves as a coolant, and the cylinder walls and heads are made of aluminum for high thermal conductivity, low mass, and affordability.