A diaphragm pump comprising: a housing having a pumping chamber containing fluid to be pumped; a transfer chamber adapted to contain hydraulic fluid, and a hydraulic fluid reservoir in fluid communication with the transfer chamber ; a cylinder ; a piston sliding in a reciprocating motion in the cylinder , the piston defining an inner piston cavity , the piston cavity having an end; a valve leading to the piston cavity , wherein the valve comprises a valve port ; a valve spool slidably mounted in the piston cavity , the valve spool covering the valve port in a first position and uncovering the valve port in a second position; a moveable spacer slidably mounted in the piston cavity intermediate the valve spool and the end of the piston cavity ; a diaphragm connected to the valve spool by a plunger and supported by the housing , the diaphragm defining a pumping chamber side and a transfer chamber side, the pumping chamber side at least partially defining the pumping chamber and the transfer chamber side at least partially defining the transfer chamber ; characterized by : a first spring in the piston cavity engaging the valve spool and first side of the moveable spacer , the first spring having a first spring constant; a second spring in the piston cavity engaging the end of the piston cavity and a second side of the moveable spacer , the second spring having a second spring constant greater than the first spring constant. a housing having a pumping chamber containing fluid to be pumped; a transfer chamber adapted to contain hydraulic fluid, and a hydraulic fluid reservoir in fluid communication with the transfer chamber ; a cylinder ; a piston sliding in a reciprocating motion in the cylinder , the piston defining an inner piston cavity , the piston cavity having an end; a valve leading to the piston cavity , wherein the valve comprises a valve port ; a valve spool slidably mounted in the piston cavity , the valve spool covering the valve port in a first position and uncovering the valve port in a second position; a moveable spacer slidably mounted in the piston cavity intermediate the valve spool and the end of the piston cavity ; a diaphragm connected to the valve spool by a plunger and supported by the housing , the diaphragm defining a pumping chamber side and a transfer chamber side, the pumping chamber side at least partially defining the pumping chamber and the transfer chamber side at least partially defining the transfer chamber ; characterized by : a first spring in the piston cavity engaging the valve spool and first side of the moveable spacer , the first spring having a first spring constant; a second spring in the piston cavity engaging the end of the piston cavity and a second side of the moveable spacer , the second spring having a second spring constant greater than the first spring constant. a first spring in the piston cavity engaging the valve spool and first side of the moveable spacer , the first spring having a first spring constant; a second spring in the piston cavity engaging the end of the piston cavity and a second side of the moveable spacer , the second spring having a second spring constant greater than the first spring constant. <EOS>