2010-07-152013-01-042011-07-152013-01-04197419741974http://hdl.handle.net/10388/etd-07152010-103652This thesis presents a study of spring valves with the ultimate aim of using them as high pressure hydraulic flow-control valves for agri­cultural applications. A closed helical coil spring, when pressurized, will provide a controlled flow between the coils when extended or later­ally deflected a given distance. Tests revealed severe longitudinal oscillations when operating in the extension mode, resulting in a very low fatigue life. The lateral deflection mode did not exhibit these oscillations but did exhibit a surge phenomenon at higher pressures. A four-way closed center spring valve was built using four exter­nally pressurized springs operating in the lateral deflection mode. A unique cable actuation system provided good proportional control with minimum deadzone and tolerancing. Tests showed that performance was acceptable up to approximately 1,000 psi but surges at higher pressures deteriorated performance. As a result of this study it is concluded that spring valves have applications at moderate pressures but operation at higher pressures is not practical.en-UStext