relatively smooth of the hydraulic piston pump

This hydraulic piston pump to run to pressures beyond 3,000 PSI / 200 BAR, making them well suited for use in hydraulics.  With four bearings in the liquid and tight tolerances, they are not well suited to handling abrasive or extreme high temperature applications.

The gear type pump Tighter internal clearances provide for a more reliable measure of liquid passing through a pump and for greater flow control. Because of this, external gear pumps are popular for precise transfer and metering applications involving polymers, fuels, and chemical additives.