Abstract: A gradient cam is used in an HPLC pump for controlling proportions of HPLC solvents on the low pressure side of the pump. The gradient cam is not concentric, and has an upward or draw slope along 190.degree. of its circumference and a downward or thrust slope along 170.degree. of its circumference. In operation, the cam is designed to be used with two followers, located 180.degree. apart, which follow along the cam's gradient. The unique cut of the cam insures a constant suction on the inlet or suction side of the cam during the entire pump cycle. During the 20.degree. period of the cycle in which both followers are simultaneously on the 190.degree. suction ridge, the slope of that portion of the gradient is one half of that of the remaining portion of the 190.degree. portion. The gradient cam provides both linear draw and output pressure.