190301g Flashcards
A hydraulic system is defined as __________
all of the interconnected hydraulic components
mounted on a vehicle or piece of equipment
A group of interconnected components within a hydraulic system that are intended to perform a specific function is called a
hydraulic circuit.
Open centre hydraulic systems are sometimes called:
constant flow systems.
One characteristic of open centre systems is high system pressure when the
directional control valve is in the neutral position.T/F
false;
Open centre hydraulic systems are most often used in applications where:
hydraulic operations are not a high percentage of the machine’s duty cycle.
Constant horsepower open centre hydraulic systems maintain a constant power draw
from the engine by varying:
varying pump displacement proportional to the load on the system.
The identifying characteristic of a closed centre hydraulic system is:
the directional control valve always blocks pump flow when it is in neutral.
Closed centre systems may be supplied with either a fixed or variable displacement
pump.T/F
true
Why are closed centre systems equipped with pressure compensated pumps often
called demand type hydraulic systems?
These systems are called demand type hydraulic systems because flow is only
provided when there is work to perform.
Why are load sensing hydraulic systems more efficient than other types of systems?
Load sensing hydraulic systems are very efficient because they provide, as closely as
possible, the precise amount of flow and pressure to perform the work demanded by
the system’s actuators.
Define the term hydrostatic transmission (HST).
A hydrostatic transmission is a rotary drive system that consists of a hydraulic pump,
which is the input component, and a hydraulic motor, which is the output component.
The difference between an open and closed circuit HST is that the path of oil flow
between the pump and motor is interrupted by the reservoir in the open circuit.T/F
true
The most commonly used HST in mobile heavy equipment is a/an:
closed circuit system with a variable displacement, reversible pump.
On HST systems that are equipped with variable displacement motors, motor torque
generation will:
be reduced as motor displacement is reduced.
List five (5) advantages of hydrostatic transmissions.
a) infinite motor speed control from maximum to zero in both directions of rotation
b) accurate motor speed can be maintained regardless of the load on the motor
output shaft
c) quicker response to speed and direction changes than any other type of
transmission
d) provides a hydrostatic lock of the motor when the output shaft speed is at zero
e) the load cannot overrun the motor when the load is being decelerated (a form of
dynamic braking)
