Hydraulic Principles MW Manual (bc) Flashcards
What is gage pressure?
Measured using atmospheric pressure as starting reference point.
Psig or kPa gauge
What is absolute pressure?
When pressure is measured using a total vacuum(absolute 0 pressure) as the starting reference point.
Psia or kPa abs
What is the difference between absolute zero and gage zero pressure?
14.7 psi or 101.325 kPA
How do you covert gage pressure to absolute pressure?
Gage pressure + 14.7 (atmospheric pressure)
What is the symbol for mercury?
Hg
What are the force-area-pressure mathematical relationships?
F=AxP
A=F/P
P=F/A
How much force does a 1 kilogram mass equal?
9.8 newtons
Describe pascals law?
When pressure is applied to a confined fluid the pressure is transmitted equally throughout that fluid, and is exerted perpendicular to every surface of the container.
How is pressure created in a hydraulic system?
Pressure is created whenever there is a resistance to fluid flow. The resistance will occurs when:
-A load is placed on linear and rotary actuators (cylinders and motors)
- an orifice in a line to control flow
- fluid moves through pipes, hoses and valves causing friction
What is the purpose of a hydraulic pump?
To produce fluid flow
What is velocity?
Velocity = distance/time
How much does 1 imperial gallon equal in cubic inches?
How much does 1 US gallon equal in cubic inches?
277 cu in
232 cu in
How is velocity measured?
Meters per second (m/s)
Feet per second (ft/s)
What is the equation to convert flow rate to velocity? Metric and imperial
Metric
Velocity = flow rate x 1666.7/area
Imperial
Velocity = flow rate/3.117 x area
Why are long bends better then abrupt 90’s in piping?
Turbulent flow is created from abrupt corners
Define friction?
The resistance to relative motion between two bodies
True or false?
The friction in laminar flow is usually proportional to the velocity?
True
What are the main causes of friction in a hydraulic system?
Excessive length of lines
Excessive velocity because the lines are to small
Excessive number of bends or fittings
Sustained flow at high pressure
What type of energy is is created from fluid moving through the lines?
Kinetic energy from the weight and velocity of the fluid
Potential energy from the pressure
Heat energy cause by friction
Fluid leaving the pump has kinetic energy and pressure energy. When fluid goes through a restriction the _________ energy is increased and the _______ energy is decreased.
Kinetic
Pressure
What does bernoullis principle state?
If the flow rate is constant, the sum of the kinetic energy and the potential energy at various points in the system is constant. Therefore whenever the velocity(kinetic energy) of a fluid increases, the pressure(potential energy) decreases.
What do hydraulic actuators do?
Convert hydraulic energy into mechanical energy.
Cylinder create linear motion
Motors create rotary motion
Describe a cylinder?
A linear actuator
Single or double acting
Tubular housing containing a piston, and sealing
One or more rods attached to the piston
Cap on one end
Head on the other end
A gland fits inside the head for the rod to pass through
How are cylinder usually sized?
Piston diameter
Piston rod diameter
Stroke length
What is the difference between single and double acting cylinders?
Single acting cylinders applies force or is pressurized in one direction only. And uses external force such as gravity, spring, or a small diameter auxiliary piston to return it
Double acting cylinders have hydraulic fluid delivered under pressure to both sides of the piston to produce force in either direction
Why is a double ended piston rod more balanced than a single piston rod cylinder?
The double ended piston rod has a rod on both sides, displacing equal amount of fluid on each side.
What is the purpose of a cusion in a cylinder?
Slow down the piston as it approaches the end of its travel
What are the symbols for the cusions?
How is cushion created?
By slowing the flow of oil being discharged.
What is the purpose of a tandem cylinder?
Allows for higher forces at the rod end without an increase in fluid pressure or cylinder diameter
What is the purpose of a retracting cylinder?
Permits a working stoke much longer than its retracted length
Cylinder force triangle
F
P A
Cylinder speed triangle
V
S A triangle
S = speed of the rod end
V = volume delivered
A = area of the effective piston surface
What is the difference between hydraulic pumps and motors?
Pumps drive the hydraulic fluid and motors are driven by the hydraulic fluid.
What types of hydraulic motors are there?
Gear, screw, vane, or piston.
What is a fixed capacity hydraulic motor?
When any variations must be controlled independently of the motor it is considered to be fixed capacity. They run at a constant rate with a predetermined flow.
What is a variable capacity hydraulic motor?
When variations can be done in the motor it is a variable capacity motor. Regardless of the flow rate they can be altered.
What are the symbols for fixed capacity motors?
One direction flow
Two direction flow
What are the symbols for variable capacity hydraulic motors?
One direction
Two direction
Are gear motors fixed or variable capacity motors?
Fixed.
Are screw Motors fixed or variable capacity?
Fixed,
Operate quit and free of vibration
What is different about a vane Motor vs a vane pump?
Because there is no centrifugal force in a cane motor springs are needed to ouch the vanes against the casing.
They can be balanced or unbalanced fixed or variable capacity
Rotary piston motors are either ________ or axial pistons?
Radial
Where does the oil enter a radial piston motor?
Through the cylinder block in the centre forcing the piston outward against the reaction ring.
During the first half rotation the piston extends the pressurized fluid enter the motor
During the second half rotation the pistons contract forcing the fluid into the reservoir line.
The cylinder block is connected to the output or driveshaft
Describe axial piston motors?
Pressurized fluid enters the valve plate forcing the pistons towards the swash plate. The angle of the swash plate determines the capacity of the motor.
During one half of the cycle pressurized fluid enters the motor as the pistons travel to their full extent.
During the other half of the cycle fluid is exhausted into the reservoir line.
The drive shaft is connected to the swash plate
What is the symbol for oscillating motors (rotary actuators)?
Also known as limited rotation motor.
What is a rotary motor designed to do?
Give a shaft rotation of less than 360 degrees. Usually consist of one vane. When fluid enters one port it pushed the vane and when the fluid enters the other port it pushes the vane back in the opposite direction.
What should be installed to help the vane from hitting the housing in a oscillating motor?
External mechanical stops
How are hydraulic motors rated?
By their displacement(size), pressure, torque, and speed.
What is displacement?
The amount of liquid handled on one rotation of the motor.
Usually measured in cubic centimetres per revolution. Cm3/rev
Cubic inches per revolution. In3/rev
Pressure requirements for hydraulic motors varies with the size of the motors ________?
Displacement
The larger the displacement of the mother the less pressure required to produce the given torque
Torque output is a function of the system pressure and the hydraulic motor _________?
Displacement
It is expressed in newton-meters (n.m)
Inch pounds per 100psi (in.lb/100psi)
How is mechanical efficiency expressed?
As a percentage
Speed (S) is expressed in _______?
How is it determined?
Rpm
Speed is determined by the flow rate rate or volume per unit of time delivered (V) divided by the motors displacement or area (A)
Effects of changes on a hydraulic motor?
What does DCV mean?
Direction control valve?