The front pump in a transmission builds up and releases hydraulic pressure to move valves in the valve body, apply clutch components, keep the transmission lubricated and provide fluid to the transmission cooler. The pump is mounted directly to the torque converter hub that turns at engine speed.
Transmission pumps usually contain an inner gear and an outer gear. The inner gear, which is turned by the torque converter hub, turns the outer gear. The turning gears create a vacuum to pressurize the fluid and power the hydraulic system. Engines must be running for the pump to work. The pump is part of the torque converter system, which keeps the engine running even when the vehicle is stopped.