Service Manual

40 ZT-4400
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uid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uidfromthecomponenthousingtothereser-
voir.
Cavitation: Aconcentratedgaseousconditionwithintheuidcausingtherapidimplosionofa
gaseous bubble.
Center Section: A device which acts as the valve body and manifold of the transmission.
Charge Pump:A device which supplies replenishing uid to the uid power system (closed
loop).
Charge Pressure:Thepressureatwhichreplenishinguidisforcedintoauid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owinonedirection.
Closed Loop:Asealedanduninterruptedcirculatingpathforuidow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formedrotorsetoperatingaboutaneccentricthatprovidesaxeddisplacementfor
pumps or motors.
Hydraulic Motor:Adevicewhichconvertshydraulicuidpowerintomechanicalforceandmo-
tionbytransferofowunderpressure.
Hydraulic Pump:Adevicewhichconvertsmechanicalforceandmotionintohydraulicuidpower
byproducingow.
Hydrostatic Pump: See “Hydraulic Pump.”
Hydrostatic Transaxle: A multi component assembly including a gear case and a hydrostati-
transmission.
GLOSSARY OF TERMS