Hydraulics Flashcards
The measure of the density of a liquid is what
Specific gravity
Pressure is measured in
Pounds per square inch PSI
What is not needed to calculate the work a hydraulic cylinder can do
Power, you need pressure x piston area = force
Pascals law states that when pressure is exerted on a confined liquid the pressure is
Transmitted equally in all directions through the liquid
Bernoullis principle states that the total energy of the fluid always remains constant. Therefore when the fluid flow in a system increases the pressure must
Decrease
A hydraulic fluid must do all of the following except
Compress easily
Hydraulic fluid that exhibits little change in viscosity is said to have a high
Viscosity index
The ability of a fluid to penetrate into the small clearance between the closely fitted parts and remain there is based on its
Viscosity
The best method of controlling hydraulic fluid contamination is the use of
Good maintenance
What will limit the hydraulic fluid oxidation
Chemical inhibitor
The ability of a filter to remove 100% of the particles from a fluid is called its
Absolute rating
When the max allowable pressure drop of a filter is reached the filter will
Permit particles through the medium
Filters are used to pick up smaller contaminant particles because
They are able to accumulate them better than strainers
Depth filters load up quick and thus
Don’t have a long service life
Why are other surface filter media sintered or fused together used in high pressure systems
They are a thick mass of material which provides support to the filtering surface
The sudden slowdown in fluid movement causes many contaminants suspended in that fluid to
Separate and settle to the bottom of the tank
The baffle is used to help circulate returning fluid around the inside of the tank this also aids in what
Fluid cooling
In order to permit efficient cooling of the fluid reservoir the
Walls should be as thin as possible
What is used to vent the reservoir to the atmosphere
Air breather equipped with a 10 micofaret? Filter
Peak hydraulic system demands are met by the use of an
Accumulator
What causes hydraulic pressure
It’s caused by the load on the system and by the resistance of the hydraulic system to fluid flow
Pump capacity is not rated in what term
PSI, they are typically rated in ,GPM
The ratio of the actual delivery rate to the theoretical displacement is called
Volumetric efficiency
What are the four major gear pump classifications
External, internal, axial flow or screw, and cycloidal
Internal gear pumps are used in hydraulic systems limited to operating pressures below
1000 PSI
Another type of pump commonly used in hydraulic systems is the
Vane pump
Flow rate through a pipe is measured in
GPM
Pressure lost in a hydraulic line depends on the
Flow velocity through the line
Hydraulic lines should never be constructed of
Galvanized pipe, it could flake
The safe working pressures of hydraulic piping are based on providing a safety factor of
6
One disadvantage of using flexible hose in a hydraulic system is
They are less permanent then piping or tube
What is used to change the direction of motion of hydraulic cylinders
Direction control valves
Directional control valves are classified in several different ways
One is the number of paths three or four
Most solenoids are only strong enough to open against a spring with a
15 pound closing force
What kind of valves are commonly used in hydraulic systems because of the construction they are partially balanced and easy to operate in a high pressure system
Spoil valves
How many primary or working connections does a three way spool valve have
Three
The three position four way valve is called
A closed crossover valve
A pressure relief valve is rated by its
Flow capacity and operating differential pressure
The flow from the outlet of a sequence valve is at blank pressure
Line
To limit the pressure to below the main part of the system you must use a
Pressure reducing valve
A shock suppressor is used in a hydraulic system as
Protection against pressure surges
Flow control valves used in a hydraulic system are usually positioned to
Meter out, regulates fluid flow on the outlet side of the actuator
A cylinder in which the retracting stroke becomes the power stroke is called what type of cylinder
Pull type cylinder
When a hydraulic cylinder is added to an existing system be sure that
The pump capacity is adequate
What is the purpose of the cushioning device used with a hydraulic cylinder
Prevent mechanical shock
All hydraulic pumps are
Positive displacement
Motor pressure ratings vary from
100-5000 PSI
The overall efficiency of a hydraulic motor is calculated how
Output hp divided by input hp
A crescent shaped separator is used on some blank gear motors
Internal gear motor
Gear motors are frequently equipped with wear plates to prevent
Internal leakage
