Hydraulics Part 2 pumps and actuators Flashcards
(115 cards)
1
Q
Describe a dynamic pump
A
There is no positive seal between the inlet and discharge
2
Q
Why must hydraulics use positive displacement pumps?
A
Because pressure must remain in the downstream lines
3
Q
What are the three types of positive displacement pumps?
A
They are classified the name of the part that does the pumping
Piston
Vane
Gear
4
Q
What three ways can the output be changed in a hydraulic pump?
A
Use a flow control and relief valve
Change the speed of the driver
Use a variable displacement pump
5
Q
What are the different types of piston pumps?
A
In line axial piston, bent axis piston,rotary piston, radial piston
6
Q
What are the two types of pumps?
A
Positive displacement, and non positive displacement, which is also known as dynamic
7
Q
What is the name of the device that tilts and varies output in an inline axial piston pump?
A
Swash plate
8
Q
What are the names of the two Pistons that regulate the pressure limiting swash plate
A
The top one (smaller one) is called the bias piston, and the other is called a compensator control piston
9
Q
What Are the three ways for controlling speed?
A
Conventional, pressure compensated, load sensing pressure compensated
10
Q
What must you do when installing a load sensing pump?
A
It must be set with 200-400 psi standby pressure
11
Q
Why should you monitor fluid viscosity in a system?
A
A decrease in fluid viscosity can lead to an increase in internal leakage
12
Q
How is the bent axis piston pump different from the inline axial pump?
A
The angle is what determines displacement. There is no swash plate, the angle of the cylinder block determines it
13
Q
What are some benefits of the bent axis piston pump?
A
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
14
Q
What are some maintenance tips for piston pumps?
A
Always prime the pump, ensure the case is full before startup, always connect case drain, maintain fluid cleanliness
15
Q
Describe how a rotary piston pump works
A
Fluid is ported in and out through the centre, while the cylinder block rotates around it
16
Q
What is the centre area of a rotary piston pump called?
A
Pintle
17
Q
What do the Pistons ride on in a Rotary piston pump?
A
A retaining ring, or reaction ring
18
Q
How is displacement changed on a rotary piston pump?
A
By moving the reaction ring because the pintle is fixed in the middle
19
Q
How does a radial piston pump work
A
The cylinder is stationary and the center cam is eccentric and rotates
20
Q
How does a vane pump rotate?
A
It has a splined rotor fitted with sliding vanes
21
Q
What are the two types of vane pumps
A
Balanced and unbalanced
22
Q
What does the vanes ride on
A
The Cam ring
23
Q
Describe the inlet and outlet ports on an unbalanced vane pump
A
There is one on each side 180° apart
24
Q
What is an advantage and a disadvantage of the unbalanced vane pump
A
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
25
What two ways are the vanes held against the cam ring?
Centrifugal force, and hydraulic pressure at the root of the vanes
26
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
27
If the balanced vane pump rotor is centered how does it create pockets?
It uses an elliptical cam
28
What is the name of the cutout on the root of the vane?
Intra vane
29
What are some benefits of the Intra vane?
More stable, less noise, less maintenance
30
What are the two types of gear pumps?
Internal gear and external gear
31
How is the pumping action created in an external gear pump?
The meshing of the two gears creates the pumping action
32
How is gear pump displacement adjusted?
It is not adjustable without a fluid bypass. You must adust the rpm of the prime mover
33
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
34
What are the two types of internal gear pumps?
The crescent seal type, and the gerotor type
35
What is the purpose of the crescent seal on the internal gear pump?
It creates the positive seal between the inlet and discharge
36
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
37
Describe the difference between single acting and double-acting cylinders
Single acting only exert force in one direction, double acting is both ways
38
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
39
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.
40
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
41
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
42
What is the purpose of the tandem cylinder
It is used for very high force and short stroke requirements
43
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
44
What is the purpose of the cylinder cushion
It is used to prevent mechanical shock
45
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
46
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
47
What is the most recommended port, and what kind of threads does it have
The O-ring boss or orb for short is the most recommended. It has a straight thread and then O-ring seal and seat
48
Where should you mount the bleed ports on a cylinder
You should try to mount the ports on top which allows any air trapped in the system to rise and escape through the port
49
Why should you check for hot spots on the cylinder?
Because it is an indicator of internal leaking of the piston rings
50
What is a hydraulic motors purpose
It converts fluid power into rotary motion
51
There are three types of motors what are they?
Low-speed, high torque (LSHT) for smooth operation under heavy loads
High-speed, low torque(HSLT) for operating continuously at constant high speeds
Limited rotation motors-used in some robotics
52
Describe the limited rotation motor symbol
It's a half circle with two arrows pointing up
53
How is displacement measured
Measured in cubic inches per revolution.
54
Describe torque
It is the rotational force of the motor. It is expressed in foot-pounds
55
What three things does torque depend on?
Inlet pressure
Surface area
Radius of rotation
56
When you gain torque, what do you lose
Lose speed, and vice versa
57
What does motor speed depend on?
Flow rate, volume
58
What are the three types of internal gear motors
Direct drive gear motors
Orbiting gear Motors
Roller vane gerotors
59
How is a sliding vane motor different from a vane pump?
The vane motor has springs under it, to make contact with the cam, as it starts too slow to use centrifugal force
60
The axial piston motor adjusts torque with the swash plate how?
At maximum angle it has low speed, high torque, and minimum angle provides maximum speed, low torque
61
Describe the radial piston motor
It is used in severe service, it's a low-speed high torque motor. It is known as a Staffa
62
What 5 things does hydraulic fluid do?
Lubricates, seals, energy transfer, heat transfer, Flushing contaminants
63
What other considerations must be taken with hydraulic fluid
It must be compatible, resist foaming, be fire resistant, and have a high viscosity index
64
Describe viscosity index
The ability for oil to maintain its properties over a range of temperature
65
What is the relativity between control and compressibility of fluids?
If the fluid is less compressible, it gives more accurate control. Some systems will use a more compressible oil, to act as a shock absorber
66
What are some characteristics of petroleum based fluids
They have a high viscosity index, are low cost and have low toxicity
67
Give some characteristics of water-based fluids
There more expensive than petroleum based, they're heavier than petroleum based, they oxidize faster, and the absorb water readily
68
Give some characteristics of synthetic fluids
They are much more expensive, they have a high resistance to oxidation, a very high viscosity index, and increased life. Most synthetic fluid's require special seal and hose material
69
What is the most prominent type of vegetable oil used
Soy oil
70
What are the main functions of the reservoir tanks
The reservoir tank is to hold a supply of fluid. It also warms or cools the fluid as needed, de-aerates the fluid, allows contaminants to settle out, reduces turbulence, and acts as a platform for the pumps and valves
71
What does the air filter on a reservoir filter down to?
3 µm
72
How is the tank made?
It is pickled and oiled (soaked in oil)
73
How big is the reservoir for an open circuit tank?
2 to 3 times the pump output
74
What is the purpose of the baffle
The barrier to direct flow from the return line away from the pump inlet. It prevents turbulence, promote cooling, promote settling, allows air to escape
75
How is the return line directed in the tank
Return flow was directed outward towards the tank wall away from the pump inlet
76
What is the inlet filter purpose
It filters down to about 100 µm. It's purpose is to remove large contaminants that could cause Pump failure
77
When you see a hydraulic symbol with arrows pointing in or out what does it mean
Arrows pointing in means heat is moving in (heater)and arrows pointing out the heat is leaving(cooling)
78
What are the three types of reservoirs
Open, pressurized, closed circuit
79
Describe a pressurized reservoir
The supply of low pressure regulated air is pumped into the tank approximately 1 to 3 PSI above atmosphere. You use these when airborne contamination is too great for the breather, or atmospheric pressure is not adequate to push fluid into the pump. It also can solve cavitation problems
80
Describe a closed circuit reservoir
Most of the return flow goes directly back to the pump from the actuator. The reservoir holds approximately three quarters of the charge pump output
81
What are the four main reservoir mounts
Flat top, L-shaped, overhead stack, vertical mount
82
Describe the vertical reservoir mount
It is the most compact design, it increases cooling because the pump is immersed in the fluid, the pump system stays cleaner, less noise and sideloading and a positive suction head
83
What are the four common sources of contamination of oil
New Oil, built-in, ingressed, generated
Ingressed=taken into system through leaky seals, dirty piston rods
Generated=wearing parts
84
How do you prevent fine filters from getting clogged too quickly?
Install a coarse filter before to trap the bulk of the contaminants
85
Why should you never use galvanized fittings in the hydraulic system
The zinc flakes off and gets in the system and reacts with the fluid
86
What is the best way to get away from thread debris
Use O ring boss fittings
87
What is iso range code?
A way to describe three different particle size levels in a sample
Eg 15/9/8
88
What is the particle sizes we measure for?
2, 5, 15 µm
89
What size microns do the most damage in the system
14,6, 4 micron particle sizes
90
What is the difference between a strainer and a filter
A strainer is usually a wire mash with pore sizes larger than 50 µm. It is used at the pump inlet another feature is that you can wash it and reuse it
91
What components does a filter consist of
Metal case containing filter element, a bypass valve, a bypass indicator
92
What are the two types of filter elements
Pleaded fiberglass cloth supported by metallic mesh, or depth type media.
93
How does depth type media work?
It does not have a constant pore size, it captures dirt by forcing the flow through a torturous where the good becomes trapped these filters are not washable and must be discarded after use
94
Why is fiberglass superior to paper as a filter?
The glass fibers can be produced much more finely, they can be laid uniformly, they resist chemical action of the fluid
95
At what colour indicator should you change the hydraulic filter?
As soon as the indicator turns yellow. This minimizes the amount of unfiltered oil through the system
96
What must the strainer equipped with
A bypass to ensure full flow to the pump when the strainer clogs
97
Where should pressure line filters be located?
Before any contaminant intolerant device such as servo, proportional, instrumentation
98
How much slow should be through the return line filter to control contamination in the entire system
20% of the total system volume should pass through the filter per minute
99
What are some of the requirements of the return line filter
Must be able to handle the maximum return line flow with minimum pressure drop. Must be a full flow filter however I return line filter is equipped with the bypass valve that is preset to divert flow
100
What is the advantage of an off-line filter
Free of pressure pulsations, can be located where it is convenient to service
101
When must you use an off-line filter system
When you use a pressure compensated variable displacement pump that is running at standby for extended periods
102
When you see a brown sticky substance on a valve what is it
Gum and varnish
103
Explain the beta ratio and filter efficiency
It is how many contaminants does it take until one passes through. For example a beta ratio of 10 means for every 10 particles one will go through for a 90% efficiency
A beta reading of 20 means for every 20 particles that get filtered one gets through for a 95% efficiency
104
What methods can be used to remove water from a system
Drain it out of the hydraulic reservoir, coalescent filters, centrifuge, absorbent filters, desiccant air breathers
105
What is the main cause of oxidation
Heat. For every 10°C you increase the temperature of the petroleum based fluid above 60°C the oxidation rate doubles
106
When O-rings are used as stationary seals how much of their diameter must project above the groove?
10%
107
What is the purpose of an accumulator
It gives the supplementary flow when demand needs it
108
What kind of air is put into an accumulator
Nitrogen
109
Accumulator precharge varies with applications define them
For energy Storage applications pre-charged to 90%
For pulsation dampening applications precharge to 70%
For shock absorption applications precharge to 75%
110
What is another name for the swashplate
Yolk
111
What instruments are required to check the system
Flow meter, pressure gauge, thermometer, tachometer
112
What is the mechanism that protects the pressure gauge called
Snubber
113
What is another name for a pipe or tube?
The fluid conductor
114
How was all tubing and hoses measured?
OD
115
What happens when the ID of tubing is decreased
The velocity decreases
