a combination tow and pressure relief valve for use in a hydraulic fluid circuit used in a hydraulically driven wide area lawn mower . the valve includes a cylindrical valve body having a hexagonal head . a slideable valve tip with a shank and a valve head has its shank slidably mounted within the valve body . the valve tip is biased by a spring to move in a direction away from the hex head . in operation , the valve is inserted into a suitable chamber placed in series with a bypass passage . the valve tends to block the bypass passage under steady state conditions . when a surge in hydraulic pressure occurs , as would occur in response to operator input or at startup , the hydraulic fluid overcomes the bias of the spring and urges the valve tip away from the otherwise blocked orifice which links the bypass passage to the chamber . opening the orifice tends to diminish the magnitude of the pressure peak and helps eliminate jerky starts of the mower . the spring eventually overcomes the reduced hydraulic fluid pressure and returns the head of the valve tip into a sealed relationship with the bypass passage orifice . a shoulder nut permits the valve to be secured at a fixed position within the chamber . varying the position of the valve within the chamber permits adjustment of the absolute value of the peak pressure which will be reached within the bypass passage . loosening the valve further permits its use as a tow valve , so that the associated mower can be moved without skidding of the mower tires or actually starting the mower engine . closing the valve further permits maximum operating pressure availability for larger and heavier equipment .