Midterm 2 Flashcards
these are located on the side of a reservoir
oil level sight glass and thermometer
the power source that drives the pump
prime mover
what determines the GPM of the pump needed in a hydraulic system?
the speed or rate at which the work must be done
what is the function of a pump?
to create flow
the ability to separate water from a liquid
demulsibility
particles grinding between moving Parts is what type of where?
abrasion
how do vary the GPM of a gear pump
vary the pump rpm
why do hydraulic reservoirs have baffles?
to slow migration of fluid to aid in Cooling
what does the cylinders capacity to lift a load depend on?
piston size and fluid pressure
any quantity of air that is in excess of the saturation level at the given pressure
entrained
the hydraulic fluid with the best natural lubricity
petroleum
the output component on a hydraulic system
actuator
gage atmospheric pressure
zero
absolute atmospheric pressure
14.7
a double acting cylinder moves under power:
in both directions
a measurement of a fluid’s resistance to flow with a change in temperature
viscosity index
what do chemical properties of a hydraulic fluid determine?
how long a fluid will function before it needs to be replaced
a single acting cylinder moves under power:
in One Direction, it needs a spring or the weight of a load to go in the other direction
what do additives in the hydraulic fluid prevent
rust and corrosion
1 bar is how many atmospheres
1.01
a valve that selectively directs or prevents fluid flow to desired locations or circuits
directional control valve
what do lines drawn to the bottom of the reservoir mean in a schematic
the line terminates beneath the fluid
how does temperature affect viscosity
heat - less viscous
cold - more viscous
if flow is constant, the sum of kinetic energy and pressure must be constant at various points in a system
Bernoulli’s principle
the best fire resistant hydraulic fluid for high temperature operation
synthetic
ISO
International standards organization
the ability to change energy from one type to another with minimal loss
efficiency of a system
how is pressure created?
flow is restricted or resisted
the PSI of a pilot valve
75 to 100
how is heat produced in a hydraulic system?
friction in the pump motor, pump, piston, and hydraulic fluid
what is viscosity of a fluid
resistance to flow
two things that could cause a liquid to flow
a pump and the weight of the liquid
what kind of valves are typical in a directional control valve
poppet, rotary, and sliding spool
what principle is the operation of piston pumps
a piston reciprocating in a bore will draw fluid in as it is drawn from the cylinder and expel the fluid as it moves back into the cylinder
what pressure is usually available to push a liquid into the pump inlet
atmospheric
rod wiper/scraper importance and materials
synthetic and polymer. it keeps foreign material from entering the system
typical size of a strainers pores
50 microns
oil and water mixing
emulsification
psig to psia
psig + 14.7
how is flow measured
GPM
effects on a system with too high a viscosity
high resistance to flow, increased power consumption, increased pressure drop, higher operating temperatures, difficulty separating air from fluid in a reservoir
what is the first component to consider in the design of a hydraulic circuit?
the acutator
what determines the speed of an actuator?
flow or GPM of the fluid
1 cubic ft of fluid is how many psi?
0.4 psi
a force exerted on a unit of area, usually expressed as pounds per square inch (psi)
pressure
what are the 2 basic types of pilot-operated check valves
pilot to open and pilot to close
what is a part of a restriction check valve
an orifice in a poppet
describe a two-stage valve
a pilot operated main stage and a pilot stage that is usually either electrically or pneumatically controlled
viscosity units
saybolt universal seconds (SUS)
centistokes (eSt)
how many basic classifications of fire resistant hydraulic fluids are there
4
the input component of a hydraulic system
pump
how to improve cycle life in check valves
they have hard steel seats and poppets
a vane type pump may have variable displacement if
it is of the hydraulically unbalanced type
a hydraulic cylinder changes hydraulic power into
straight in-line motion
what are 4 advantages of a hydraulic system
reversible while in motion, overload protection while maintaining output force, infinitely variable speed, high power in a relatively small, lightweight package
what is the purpose of cylinder cushions
to prevent the piston from hammering the end caps
what does a relief valve do
prevents overload of the prime mover, prevents pumps and other components from being damaged
the 4 primary purposes of hydraulic fluid
transmit power, cool and dissipate heat, seal clearances between parts, lubricate moving parts
directional control valves are sized by
the nominal size of the ports
