A high viscosity portion pump system has a single piston portion pump having a piston/diaphragm assembly arranged on a piston shaft forming liquid and gas chambers, which moves from a starting-position and provides high viscosity fluid from the liquid chamber when gas is received by the gas chamber; has an elastic member arranged on a retainer coupled to the shaft in a compartment in a pump housing, which moves the assembly back to the position and draws further fluid into the liquid chamber when the gas is released; and has a piston position sensor that responds to the position of the shaft and provides signaling containing information about when the assembly is in the position or completed a stroke from the position. A gas control system includes a signal processor that receives the signaling, and provides corresponding signaling containing information about when to provide or release the gas.