Inside a classic external gear pump, pressure induced forces push the
gears against the housing, causing characteristic wear of the suction
side. Even new pumps present this type of wear, which is
completely normal, and allows us to distinguish with one hundred
percent certainty the pressure side from the suction side.
As a rule this wear is measured in tenths of
millimeter, however the "Commercial/Parker" you see to the left
measures the same wear in centimeters, proving once again that there
are hydraulic equipment owners out there, who consider shutting down a
prime mover when a function problem is detected an absolutely
unnecessary precaution.