Service Manual

127P Series
GLOSSARY OF TERMS
Axial Piston: Type of design for hydraulic motors and pumps in which the pistons are arranged
parallel with the spindle (input or output shaft).
Bypass Valve: A valve whose primary function is to open a path for the fluid to bypass the motor
or pump. Also referred to occasionally as the freewheel valve or dump valve.
Case Drain Line (Return Line): A line returning fluid from the component housing to the reser-
voir.
Cavitation: A phenomenon of boiling in a flowing liquid at normal temperatures, as a result of low
pressure condition. The gas liberated from the fluid implodes rapidly and damages pump compo-
nents.
Center Section: A device which acts as the valve body and manifold of the transmission.
Charge Pump: A device which supplies replenishing fluid to the fluid power system (closed
loop).
Charge Pressure: The pressure at which replenishing fluid is forced into a fluid power system.
Charge Relief Valve: A pressure control valve whose primary function is to limit pressure in the
charge circuit.
Check Valve: A valve whose primary function is to restrict flow in one direction.
Closed Loop: A sealed and uninterrupted circulating path for fluid flow from the pump to the
motor and back.
Decay Rate: The ratio of pressure decay over time.
End Cap: See “Center Section.”
Entrained Air: A mechanically generated mixture of air bubbles having a tendency to separate
from the liquid phase.
Gerotor: A fixed displacement pump frequently used as a charge pump.
Hydraulic Motor: A device which converts hydraulic fluid pressure and flow into mechanical
force and motion.
Hydraulic Pump: A device which converts mechanical force and motion into hydraulic fluid pres-
sure and flow.
Hydrostatic Motor: See “Hydraulic Motor.”
Hydrostatic Pump: See “Hydraulic Pump.”
Hydrostatic Transaxle: A multicomponent assembly including a gear case and a hydrostatic
transmission.