A pumping system for a hydrothermal biomass converter comprising one or more cylinders, each cylinder having an inlet end and an outlet end, and each cylinder having both a low pressure valve and a high pressure valve at both the inlet and the outlet end respectively, and each cylinder comprising an inner hydraulic actuator segment (1) which is separated from an inlet segment (2) on the inlet end and from an outlet segment (3) on the outlet end by a lower-pressure zone (8) sealed by two or more gaskets (7). Each cylinder further comprises an axially displaceable piston (5) fitted with a piston ring (6), which piston is adapted to move back and forth within the hydraulic actuator segment (1) so as to alternately displace volume in the inlet segment (2) when piston movement is towards the inlet end and in the outlet segment (3) when piston movement is towards the outlet end. When applied to a hydrothermal biomass converter, a biomass feed input system is in fluid communication with each of the low pressure valves at the inlet ends of the one or more cylinders, and a product output system is in fluid communication with each of the low pressure valves at the outlet ends of the one or more cylinders.