Neptune's 600 Series Hydraulic Metering Pumps are designed for high-pressure, high-volume applications and are available in simplex & duplex. The pumps in the 600 series are adjustable capacity by using the micrometer dial that can be varied while running or when stopped. Variable Oil By-Pass™ Stroke Adjustment provides increased valve performance in comparison to variable linkage designs. This performance improvement results from valve checks that allow extra time to seat even in viscous fluids since they are idle during the by-pass portion of the suction & discharge strokes. They also use a hydraulically-balanced PTFE diaphragm to eliminate stress. Materials of construction options include: 316 Stainless Steel, Carpenter-20, PVC or PVDF Liquid Heads & PTFE Diaphragm. Capacities range from 126 gph (477 L/h) to 240 gph (908 L/h). Maximum Temperatures & Pressures: 316SS & C-20 - 200°F (93°C), 600 psi; PVC & PVDF- 125°F (52°C), 150 psi. Max Pressures apply on certain models.