Module L Flashcards
Pressure is defined as:
force per unit area
Pressure is calculated by:
Dividing the force by the area over which the force is distributed or P=F/A
The amount of work is equal to:
The distance moved (in m or ft) times a force exerted (in N or lbf)
What does ISO stand for?
International Organization for Standarization
A ______________ is a linear actuator.
Cylinder
Cylinders are available with either _____________ or ______________ motion
single or double-acting motion
Describe the housing of a cylinder
It is sealed with a cap on one end and the head on the other end
What is the difference between single and double acting cylinders?
Single: applies force in one direction only
Double: Have hydraulic fluid delivered under pressure to both sides of the piston.
Force exerted by the piston is different from one side to the other.
In a cylinder, the cross-sectional area of a piston rod is __________the piston face area
less than half
If the cross sectional area is more than half the piston face area, it is considered a ___________
ram
How can a rod be returned in a single acting cylinder?
Spring return
If there is the same fluid supple exists on each side of a cylinder, why is the speed of the piston different when extending vs retracting?
Because the piston rod takes away some of the surface area from the piston and also creates a smaller cavity for the fluid to fill.
In a single piston rod, the force exerted by the piston is ________ on the side with the piston rod
less
In a ____________________, where the rods are the same diameter, the forces on the piston can be the same
double-rod cylinder
Double-acting cylinders are often designed with a _______________to slow down the piston as it approaches the end of its travel.
cushioning device
________________ have two pistons attached to one rod.
Tandem cylinders
What is the purpose of a tandem cylinder?
This design allows for higher forces at the rod end without an increase in fluid pressure or cylinder diameter
What orientation should a cylinder be mounted in?
Any position, provided they are mounted on a strong and rigid base and aligned with the part they are to move
What should a millwright do when designing or troubleshooting hydraulic circuits?
calculate cylinder forces and speeds
What unit is cylinder speed measured in?
inches/minute (if the area is in imperial)
How do you calculate cylinder speed?
cylinder speed= flow rate x 231/area
What is the main difference between hydraulic pumps and hydraulic motors?
Pumps drive the hydraulic fluid
Motors are driven by hydraulic fluid
In a hydraulic motor, a __________ oil supply to the motor allows the motor to be run over a wide range of speeds
Variable
Oscillating motors are designed to give a shaft rotation of _______________
less than 360 degrees
Oscillating motors are also called
rotary actuators
When designing and troubleshooting circuits, millwrights must be aware of these 5 factors
- displacement
- Pressure
- torque
- mechanical efficiency
- Rotary speed
_______________ is the amount of liquid handled in one rotation of the motor
displacement
displacement is usually expressed in __________________
cubic centimeters per revolution (cm3/rev) or cubic inches per revolution (in3/rev)
Torque output is a function of the system pressure and the _____________
motor displacement
Torque is expressed in _____________
newton-meters (N.m) or inch-pounds (in.lb)
How do you calculate mechanical efficiency?
mechanical efficiency = actual torque delivered/theoretical torque x 100%
How is rotary speed determined when using imperial units?
speed= flow rate x 231/area
If using the metric system, the flow rate is measured in liters per minute. To calculate the rotary speed when using metric units, the equation is ____________
Rotary speed= flow rate x 1000/area
What is used to control the direction of hydraulic fluid flow?
Direction control valves (DVC)
What are the two types of DVCs?
- Single position- Maintains uni-directional flow pattern
- Multiple position- Start, stop or change direction of flow to or from hydraulic actuators
What type of DVC is a check valve?
single position
What symbol represents a transitory condition that a valve passes through, but does not stop in the position.
An envelope with dashed ends
What are the four types of check valves?
- Free check
- Spring Loaded
- Restricted flow
- Pilot-controlled types
What is the benefit of a spring loaded check valve?
Because it uses a light spring to hold the valve seated regardless of its mounting position. A free check valve uses gravity and must be mounted correctly.
Check valves with ____________________ typically used to control the rate of decompression before shifting (activating) the main DVC.
Restricted flow