Hydraulics Part 2 pumps and actuators Flashcards
Describe a dynamic pump
There is no positive seal between the inlet and discharge
Why must hydraulics use positive displacement pumps?
Because pressure must remain in the downstream lines
What are the three types of positive displacement pumps?
They are classified the name of the part that does the pumping
Piston
Vane
Gear
What three ways can the output be changed in a hydraulic pump?
Use a flow control and relief valve
Change the speed of the driver
Use a variable displacement pump
What are the different types of piston pumps?
In line axial piston, bent axis piston,rotary piston, radial piston
What are the two types of pumps?
Positive displacement, and non positive displacement, which is also known as dynamic
What is the name of the device that tilts and varies output in an inline axial piston pump?
Swash plate
What are the names of the two Pistons that regulate the pressure limiting swash plate
The top one (smaller one) is called the bias piston, and the other is called a compensator control piston
What Are the three ways for controlling speed?
Conventional, pressure compensated, load sensing pressure compensated
What must you do when installing a load sensing pump?
It must be set with 200-400 psi standby pressure
Why should you monitor fluid viscosity in a system?
A decrease in fluid viscosity can lead to an increase in internal leakage
How is the bent axis piston pump different from the inline axial pump?
The angle is what determines displacement. There is no swash plate, the angle of the cylinder block determines it
What are some benefits of the bent axis piston pump?
It is the most rugged design, it can withstand high vacuum at the inlet, so it can be mounted above the fluid level in the reservoir
What are some maintenance tips for piston pumps?
Always prime the pump, ensure the case is full before startup, always connect case drain, maintain fluid cleanliness
Describe how a rotary piston pump works
Fluid is ported in and out through the centre, while the cylinder block rotates around it
What is the centre area of a rotary piston pump called?
Pintle
What do the Pistons ride on in a Rotary piston pump?
A retaining ring, or reaction ring
How is displacement changed on a rotary piston pump?
By moving the reaction ring because the pintle is fixed in the middle
How does a radial piston pump work
The cylinder is stationary and the center cam is eccentric and rotates
How does a vane pump rotate?
It has a splined rotor fitted with sliding vanes
What are the two types of vane pumps
Balanced and unbalanced
What does the vanes ride on
The Cam ring
Describe the inlet and outlet ports on an unbalanced vane pump
There is one on each side 180° apart
What is an advantage and a disadvantage of the unbalanced vane pump
And advantages it has a movable cam ring which allows for variable displacement. Disadvantage is it requires large bearings and casing to support the unbalanced load
What two ways are the vanes held against the cam ring?
Centrifugal force, and hydraulic pressure at the root of the vanes
Why is the balanced vane pump much more compact?
It has two pumping chambers that are 180° apart so the forces at one outlet act against the forces on the opposing outlet
If the balanced vane pump rotor is centered how does it create pockets?
It uses an elliptical cam
What is the name of the cutout on the root of the vane?
Intra vane
What are some benefits of the Intra vane?
More stable, less noise, less maintenance
What are the two types of gear pumps?
Internal gear and external gear
How is the pumping action created in an external gear pump?
The meshing of the two gears creates the pumping action
How is gear pump displacement adjusted?
It is not adjustable without a fluid bypass. You must adust the rpm of the prime mover
Why are radial loads high on gear pumps?
Because of the highly unbalanced hydraulic pressures from the inlet to discharge side. Therefore they use heavy needle bearings or bushings to support those loads
What are the two types of internal gear pumps?
The crescent seal type, and the gerotor type
What is the purpose of the crescent seal on the internal gear pump?
It creates the positive seal between the inlet and discharge
Describe the gerotor internal gear pump
It’s used mainly as a charge pump, has a star shaped rotor with one less tooth than the lobes on the outer gear
Describe the difference between single acting and double-acting cylinders
Single acting only exert force in one direction, double acting is both ways
Describe the characteristics of a telescopic cylinder
It is a series of sleeves nested together, provides a long stroke but very compact when retracted. As it extends the speed increases and force decreases due to the diminishing diameter of each sleeve
Describe a differential cylinder
Has the cap end on one side, and rod end on the other. More force is created on the cap end due to the larger area.
What is a double rod cylinder?
It is a non-differential cylinder so it produces equal force in speed in both directions. It can push and pull simultaneously
What is The difference between the rod seal and the rod wiper?
The rod seal keeps the fluid inside the piston, and the rod wiper keeps contaminants out
What is the purpose of the tandem cylinder
It is used for very high force and short stroke requirements
Describe cylinder cushion
When the plunger comes to the end it plugs off the flow of fluid which is then forced to go through a small controlled opening that is adjustable similar to a meter out flow control
What is the purpose of the cylinder cushion
It is used to prevent mechanical shock
What is the purpose of a stop tube
It is a metal collar that fits over the piston rod next to the piston it is used to reduce sideloading on longer rods
What is the two types of Rod supports and what is their function
Center support, and tie rod support. They are used to provide rigidity for long stroke cylinders