hydraulic actuator Flashcards
two main types of single acting cylinders
piston and ram
piston type cylinders
consists of a piston and a rod that slides up and down the barrel . piston seal rings on the piston center it and act as a wear surface
what could cause a differential cylinder to drift while in the hold position
leaking piston seals
most common cause of cavitation failure in a hydraulic motor
when the motor rotates faster then the the pump can provide oil
cylinder cushions
are used to slow down the hydraulically operated implement by restricting the rate of return oil and creating a back pressure that resist piston movement
ram type cylinders
simpler and more commonly used consists of a piston that slides within a cylinder barrel .
the amount of torque a motor can produce depends on
motor inlet pressure and motor displacement
why can a piston motors swash plate never reach a perpendicular position
because the motor would become hydrostatically locked . plate angle is limited to 6.5 to 19 degrees from perpendicular
under a constant flow rate what is the relationship between speed and displacement
if speed increases . motor displacement decreases
if you suspect the piston seals of a cylinder are leaking you should
measure the amount of return oil while the cylinder is being stalled
most common use for cylinder reliefs
used on systems that have limited reservoir capacity witch would limit cooling capacity of the system
double acting single rod cylinders are often referred to as
differential cylinders . because of the difference of retraction vs extension speed and force
force and speed of cylinder movement changes depending upon
what stage is moving . first stage being the largest has the most force but moves the slowest . each successive stage force is decreased and speed is increased
what is the difference in vane construction from a pump to a motor
vane motors rely on spring pressure to keep the vanes against the cam ring during start up
double acting cylinders
are both hydraulically extended and retracted
gerotor motors
have low rpm high torque consist of a spool valve a gerotor star
geroller motors
have low rpm and high torque have a disc valve to direct oil flow and uses rollers in the housing to assist in less internal friction of the geroller stars movement
piston reliefs
allow pump oil flow to bypass the piston when it reaches the end of its stroke
telescoping single acting cylinders
used to obtain additional stroke length in a compact package . constructed with two or more cylinders called stages
double acting double rod cylinders
has equal volume and piston area on both sides . also known as non differential cylinder
single acting cylinders
are hydraulically actuated in one direction and require some other force to cause the piston to move in the opposite direction
piston relief valves are
double check valves that open when the piston reaches the end of its stroke and close when in mid range of operation
hydraulic motor operating principles
converts hydraulic energy into rotary mechanical energy . by converting oil flow and pressure into speed and torque
what are some additional cylinder features
quick drop . cylinder cushions . piston relief
how are dirt and contamination prevented from entering the cylinder
dirt seal on the outer end of the cylinder barrel
when removing the rod and piston assembly from a hydraulic cylinder you should not use
compressed air . piston my leave the barrel assembly at extreme velocity
what is the relationship between motor displacement and torque generation in a motor
torque increases proportionally to the increase of motor displacement
how is the flow of oil directed through a ram type cylinder
oil flow is directed into the inlet and outlet port to extend the cylinder to retract the cylinder oil flow from the outlet/ inlet is connected to the reservoir
quick drop valves
provide faster lowering cycle times on implements
contamination failure of a motor
components will appear dull and sandblasted
how dose a quick drop valve operate
by supplementing pump flow to the base of the cylinder by redirecting rod end return flow to the base end known as regeneration through the use of a spool valve and spring loaded plunger
