All models are pneumatically driven piston pumps that deliver the maximum volume of lubricant per stroke. Pneumatic solenoid valves and adjustable solid-state timing are integrated into the pump body. These pump units are designed to deliver grease to single-line metering devices and feature a special fitting for large-volume filling. Transparent acrylic reservoirs with spring-loaded pressure plates are available in several sizes. The pump uses compressed air for both forward and reverse strokes, but dispenses lubricant only during the forward stroke. During the reverse stroke, pressure is released from the lubrication line through a built-in check/relief valve.