Hydraulics Flashcards
1
Q
This is required to move a stationary object or change how fast an object moves
A
Force (expressed in newtons or pounds)
2
Q
Defined as the force per unit area
A
Pressure (expressed as N/m², psi, or bars) kPa or bars most common
3
Q
Atmospheric pressure
A
14.7 psi (101.35 kPa, 1.01 bar)
4
Q
Energy cannot be destroyed, but may be converted from one form to another
A
Law of conservation of energy
5
Q
Unlike a gas, a liquid is virtually _______
A
incompressible
6
Q
Hydraulic fluid compresses about __% at 1000 psi
A
1/2%
7
Q
Pressure applied to a confined fluid at rest, force is transmitted equally in every direction and always at right angles to the containing surface
A
Pascal’s Law
8
Q
How is flow rate expressed
A
litres per minute or gallons per minute
9
Q
Refers to the average speed of the hydraulic fluid passing a given point. This is the distance travelled by the fluid in a unit of time
A
Velocity
10
Q
The fluid moves in layers parallel to the walls
A
Laminar flow
11
Q
When the fluid particles move in a random pattern
A
Turbulent flow (caused by high velocity, obstructions, sharp bends etc.)
12
Q
The main causes of excessive friction in hydraulic lines
A
Excessive length of lines
Excessive velocity (lines too small)
Excessive number of bends or fittings
Sustained flow at high pressure
13
Q
If the flow rate is constant, the sum of the kinetic energy and the potential energy at various points in the system is constant
A
Bernoulli’s Principle
14
Q
Components of hydraulic systems that convert hydraulic energy into mechanical energy
A
Hydraulic actuators (cylinders for linear motion motors rotary motion)
15
Q
If the cross-sectional area of the rod is more than half the piston face it is considered this
A
A ram (or plunger)
16
Q
In a single-rod double acting cylinder which side is slower
A
Extension side is slower
17
Q
What is the point of a cushion
A
Slows down the piston as it approaches the end of travel
18
Q
Cylinder that has two pistons attached to one rod
A
Tandem
19
Q
Pumps ____ the hydraulic fluid and motors are _____ by the hydraulic fluid
A
Drive, driven
20
Q
How are DCVs numbered
A
3 /2 = 3 way valve (3 ports) with 2 positions
Spool types - sliding or rotary
21
Q
These DCVs allow the spool to pass through from one envelope to another at any given rate
A
Throttling (infinite positioning). Indicated by parallel lines above and below the envelopes. Example is a Tracer valve
22
Q
These DCVs snap into only one of the envelopes at a time
A
Non-throttling
23
Q
DCV all ports are blocked off in neutral, locks actuator
A
Closed centre
24
Q
DCV all ports are connected in neutral, actuator moves in direction of external forces
A
Open centre
25
DCV actuator ports are blocked off, flow from pump is back to the tank
Tandem centre
26
DVC ports A and B are connected to tank, and pump is blocked off, actuator coasts to a stop or moved manually
Float centre
27
DVC ports A and B are connected to pump, maintains constant pressure to both ports of actuator
Regenerative centre
28
Single position valves which allow free flow in one direction only
Check valve (common styles are ball or poppet)
29
Spring loaded check valves use a spring force of this
34kPa (5psi)
30
These valves control the hydraulic pressure in all or part of the circuit
Pressure control valve (one single square)
31
The difference between cracking pressure and full flow pressure is called this
Pressure override or pressure differential
32
The two basic designs of maximum pressure relief valves
```
Direct acting (simple relief) valve
Pilot-operated (two stage)
```
33
Used if a large amount of fluid is to be relieved under a small pressure differential
Pilot-operated pressure relief valve
34
This valve returns pump output to the reservoir after the required system pressure has been reached
Unloading valve
35
Valves used to control vertical cylinders that are loaded so they don't fall freely due to gravity
Counterbalance valve
36
The simplest and most finely adjustable type of throttle valve
Needle valve
37
A common method of controlling the amount of fluid passing through an orifice as the temperature changes
Temperature compensating rod
38
A magnet in which the magnetic lines of force are produced by an electric current
electromagnet (solenoid)
39
The solenoid-controlled pilot valve is called this
Master valve
40
This type of solenoid allows the operator to vary the position of the plunger by varying the amount of current to the solenoid
Proportional solenoids
41
Pressure in a hydraulic system is created by this
Resistance to flow (pump can produce flow but not pressure)
42
This type of filter has only a portion of oil passing through the filtering element
Proportional filter
43
This type of filter has all the oil pass through it
Full-flow (often has a bypass valve for when filter get clogged)
44
These filters are considered coarse filters or strainers
Mechanical (metal) filters (remove larger particles, not water or fine)
45
These filters contain paper, wood pulp, fabric or wool and remove fine particles and water
Absorbent (inactive) filters
46
These filters remove impurities by both mechanical and chemical means
Adsorbent (active). May also remove additives in hydraulic fluid
47
The smallest particle that can be seen
40 microns
48
The three positions for putting filters
Inlet side, pressure side, and return line side
49
The volume of fluid in the reservoir is normally equal to this
Two to three times the rated pump delivery for one minute
50
Recommended height of the baffle plate
Two-thirds the height of the minimum fluid level
51
Recommended height of the return and suction lines from the bottom of tank
1-1/2 to 2 times the pipe diameter
52
These store fluid under pressure for future use as a source of potential energy, as well as absorb shock waves
Accumulator
53
Three types of accumulators
Weight-loaded
Spring-loaded
Pneumatic or gas-charged (use Boyle's law)
54
These operate as a force multiplier
Pressure intensifier
55
In hydraulic systems these three conditions are measured
Pressure, flow, and temperature
56
The most common electrical interface device found in hydraulic systems
Pressure activated electric switch
57
The most common hydraulic fluid
Petroleum
58
The heaviest of of hydraulic fluids and require special pump inlet designs
Synthetic
59
What type of pipe should not be used
Galvanized because scales or flakes of zinc can enter system
60
How should you seal a pipe connection
Starting 2 threads from the end of the pipe
61
How is tubing sized
By the OD (fractions of an inch or dash numbers)
62
SAE and JIC flare angles
```
SAE = 45 (90 included angle)
JIC = 37 (74 included angle)
```
63
The correct bend radius for tubing
3 to 4 times the tube OD
64
The inner tube of a hose can withstand these temps
133 C (275F)
65
Flow triangle equation
V
SA
```
V= Flow rate in inches cubed/minute
S= Speed in inches/minute
A= Area in inches square
```
66
Type of relief valve commonly used in hydraulic systems operating above 500psi and flow above 3 gpm
Pilot-operated pressure relief valve (minimize pressure override)
67
1 micron =
0.000039
68
The flow paths in a valve are commonly called this
Ways
69
When are pilot operated control valves necessary
To control direction of flows above 20 or 25 GPM
70
Check valve gpm range
in-line = 100 gpm
| right angle = 3 times as much as in-line
71
The three flow control methods
Meter-in, meter-out, and bleed-off
72
The two types of pressure compensators
Bypass and restrictor
73
Capacity of screw and slip in cartridge valves
screw in = 30 to 35 gpm
| slip in = over 30 gpm
74
Conventional solenoid controlled valves are sometimes called this
Bang bang valves
75
For proportional solenoids the movement is proportional to what?
The electrical input
76
Gain output
1000000 the input voltage
77
What does a servo valve use to operate the valve instead of a solenoid
A torque motor (much more accurate)
78
The three types of servo valves
flapper nozzle, jet pipe, staging spool
79
Three stage servos can handle flows as high as this
1000 gpm
80
What do you call a cylinder with unequal area on each side
Differential cylinder
81
The efficiency of a external gear motor should be at least this
85%
82
The two classes of pumps in industry
Positive displacement and non-positive (dynamic)
83
Which pumps are not suitable for hydraulic systems
Non-positive (dynamic)
84
What does a positive displacement pump have that non-positive don't
A positive seal between inlet and outlet
85
Controlled leakage percentage in a positive displacement pump
5% to 15%
86
Types of positive displacement pumps
Piston, vane, and gear
87
Types of piston pumps (4)
in-line axial, bent axis, rotary, radial
88
On a load sensing pump what is the standby pressure needed
200 to 400 psi
89
Types of vane pumps
- Balanced (two pumping chambers 180 degrees apart, displacement not adjustable)
- Unbalanced (minimum 600rpm, must have large casing and bearings)
- Cartridge
90
Types of gear pumps
Internal gear and external gear
91
Internal gear pump with star-shaped rotor
Gerotor (quietest gear pump)
92
Efficiency of gear pumps and piston pumps
```
Gear = 85%
Piston = 90-95%
```
93
Which end of the pump is direction of rotation defined
Drive end
94
Types of pressure control valves (5)
```
Relief
Pressure reducing
Sequence
Counterbalance
Brake
```
95
sometimes called a hydrostat
pressure compensator
96
What can a bent axis pump withstand that an in-line cant
High vacuum at inlet
97
Are gear pumps fixed or variable displacement
Fixed
98
Which pump has a crescent seal type
Internal gear (inner gear has less teeth than outer as well)
99
What does increasing swash plate angle do
Increase stroke
100
Which piston pump has check valves in the pistons
Radial
101
Rings used when no creep is tolerated in a cylinder
Synthetic
102
What may be used on a cylinder with a long rod that magnifies side loads
Stop tubes
103
Best port connections for hydraulic cylinders
ORB
| NPTF if using tapered
104
Should the cylinder ports be mounted on the top or bottom
Top
105
Types of hydraulic motors
LSHT (low speed high torque)
HSLT (high speed low torque)
Limited rotation motors
106
The amount of fluid required to turn the output shaft one revolution is called
Displacement
107
The three types of internal gear motors
Direct drive
orbiting gear
roller vane
108
Plumbing tube K, L, M thickness
K - thick
L - medium
M - thin
109
A full vacuum hose is rated for this
28 inches of mercury
110
Type of hose for pump inlet
Vacuum
111
Recommended maximum velocities
Maximum pump inlet - 2 to 4 feet/second
| Maximum pressure line - 7 to 20 feet/second
112
Immediately recognized by a rattling sound and confirmed by abnormally low pressure at pump inlet
Cavitation
113
What to use when regular hydraulic oil is not available
Automatic transmission fluid (ATF) or engine crankcase oil
114
Hydraulic tanks are made from this
9 or 11 gauge steel
115
Water coolers are also called this
Shell and tube heat exchanger
116
Three types of reservoirs
Open
Pressurized (1 to 3 psi above atmosphere)
Closed-circuit (only 15% of flow back to tank)
117
4 types of mounting styles for reservoirs
Flat top (power pack)
L shaped
Overhead stack
Vertical mount (compact, pump inside reservoir)
118
Percentage of hydraulic component failure due to contamination
80%
119
Micron sizes that do the most damage
14, 6, 4
120
Metal to metal seal leakage percentage
5-15%
121
Accumulator charge levels
Energy storage applications - 90% of minimum working pressure
Pulsation dampening -70% of normal working pressure
Shock absorption - 75% of normal working pressure
Never less than 25% of max system pressure
122
Small lines and passages in valves are called this
Pilots
123
What kind of relief valve is used in a system with an accumulator
Unloading
124
Are pressure reducing valves normally open or normally closed
Normally open
125
Difference between a sequence valve and a counterbalance
Counterbalance has an internal drain, sequence has an external drain
126
Where are counterbalance valves located
The loaded end of the cylinder
127
What do pilot chokes do on a DCV
Control shift speed of the spool
128
Order of valves in a stack valve
Bottom - relief
Middle - flow
Top - directional
129
This valve is also known as a high-low circuit
Unloading valve
130
Bypass compensators only works for this kind of flow control
Meter-in (Restrictor compensators work for both meter in and meter out)
131
The two automatic swash plate controls are
Pressure limiting compensator (limits maximum pressure in the system, saves energy)
Load sensing compensator (Can be used with pressure limiting compensator)
132
Are radial piston pumps variable or fixed
Both (require large volumes)
133
When do unbalanced vane pumps need springs to seal
Below 600rpm
134
The two common causes of vane pump failure
Contamination, aeration/cavitation
135
Used as a charge pump
Gerotor
136
Most common industrial mount
Tie rod mount
137
Motors that have been modified to turn only part of a revolution
Limited rotation motors
138
Staffa is a type of what
Radial piston motor
