Hydraulics Flashcards
Two basic types of hydrostatic motors are what?
Piston and vane
A turbine motor is also called a what?
Hydrokinetic motor
A motor that spins forward and reverse is called what?
Bidirectional
What are 2 categories for pneumatic tools?
Percussive and rotary
Give an example of a percussive and rotary tool?
Percussive- air hammer
Rotary- impact wrench
A cylinder converts…..
Fluid power stored energy into straight line mechanical energy
How does a check valve work?
Allows air to flow only in 1 direction
Stroke adjusters limit stroke only in….
The retract position
Most popular type of cylinder?
Double acting cylinder
When cylinder rod is extended it is called the what?
Thrust load
When cylinder rod is retracted it is called the what?
Tension load
What bad thing can happen when the cylinder rod is fully extended?
Buckling from rod sag
To power a double acting cylinder in both directions you at least have to have a what?
4 way DCV
What is a popular primary seal?
Lip seal
What does a wiper seal do?
Keeps contaminants from entering that managed to pass through the primary seal
Name 3 cylinder mounting styles
Trunnion, clevis and side lug
3 reasons rod buckling can happen?
- Diameter of the rod
- Way cylinder is mounted
- Forces being applied
What are 2 compressor types?
Displacement and dynamic
Most common type of positive displacement compressor found in an industrial pneumatic system is what?
Reciprocating piston compressor
What do vane compressors do?
Generate pumping action by causing vanes to track along circular housing
Difference between motors and compressors?
Motors have the smallest volume chamber.
Compressors have the largest to smallest volume chamber
What are centrifugal compressors used for?
Moving large amounts of air at low pressures
5 unloading methods?
- Bypass
- Stop start
- Inlet throttling
- Inlet valve regulation
- Inlet closure
What do cushions do?
Slows down cylinder at the end of stroke, prevents shock
Contaminants in a pneumatic system come from 3 basic sources…
1) built-in
2) generated
3) ingested
How does built-in dirt occur?
In newly fabricated systems where components are dirty or where installation practices are below standard.
How is dirt generated?
As a system operates, moving parts come in contact with other surfaces begin to wear. The use use of incorrect fluid conductors may cause rust.
How does ingestion work?
When something like a valve breaks down and a maintenance man replaces it, he will most likely be working in a dirty environment.
What are 2 contaminant types?
Dirt and liquid
What is the first line of defense for industrial compressed air?
Intake filter and aftercooler.
When should you change a filter?
When the pressure difference is 10 psi or more.
What does ‘FRL’ stand for?
Filter, regulator, lubricator
Why is proper lubrication necessary?
It is needed to coat the seals to reduce friction significantly extending their life.
Most pneumatic cylinders and motors require lubrication to prevent what?
Friction and scoring.
What are the two categories of fluid power?
Hydraulics & pneumatics
What are the three things that fluid does?
- It flows
- Takes the shape of its container
- Exerts a pressure
Difference between liquids and gases?
Liquids have a fixed volume and cannot be compressed, gases can be compressed.
Definition of pressure?
Force per unit area
3 ways pressure can be created?
- Force applied
- Column of fluid
- Resistance to flow
Definition of a vacuum?
Any pressure less than atmospheric
Definition of an orfice?
Any restricted passage
The amount of flow through an orfice is determined by 4 thing?
- Size of orfice
- Viscosity of fluid
- Pressure drop
- Temperature
What is Boyles law?
As volume increases, pressure decreases
What slows down the cylinder at the end of its stroke?
Cushion valves
Check valves allow what?
Flow in only one direction
In a multistage compressor which piston is larger?
The 1st stage is always larger than the 2nd stage
What is the benefit of having a multistage compressor?
Builds more pressure.
Pressure is measured in what?
PSI
Flow rate in pneumatics is measured In what?
CFM
You control pressure at what 2 points?
At the compressor and after the receiver tank
What are the 3 types of center conditions?
- Blocked
- Exhaust
- Pressure
Flow controls are in 2 major categories, what are they?
- Fixed
- Adjustable
Give an example of fixed and adjustable flow controls.
Fixed - orfice plate
Adjustable - needle valve
This valve increases exhaust flow in a dcv?
Quick exhaust valve
Air is drawn into a fluid power motor by what?
The smallest volume chamber
To power a double acting cylinder you have to have at least a what?
4 way dcv
Formulas for pressure, force and area?
Force - P x A = F
Pressure - F/A =P
Area - P/F = A
What device cools between multistage compression?
Intercooler
Which device cools after compression?
Aftercooler
Which valve unloads pressure from compressor head when compressor shuts off?
Unloading valve
If unloading valve does not shut off than what is wrong?
Bad check valve
Most common non-positive displacement motor?
Centrifugal
Limiting flow in a fluid power system means you limit what?
Speed
Limiting pressure in a fluid power system means you limit?
Force
3 things that a valve controls?
- System pressure
- Direction of flow
- Rate of flow
Adjustable valve that only deals with down stream pressure is what?
Regulator
Non-adjustable valve that only deals with upstream pressure?
Safety relief valve
What do cushion valves protect against?
Shock and hammer
What are 3 types of contamination?
- Built in
- Generated
- Ingested
What does FRL stand for?
Filter, regulator, lubricator
Why do we use lubrication?
To lubricate seals, reduce friction and heat and to extend the life of something
What are good work practices?
Put parts on rags on their sides, wrap zip ties around hoses to be able to identify where they go.
What do you always have to have after an aftercooler?
Moisture separator
How should you always meter flow to a cylinder?
When in doubt meter out
Definition of a valve?
Consists of a body and a moving part which connects and disconnects within the body
Best place for a flow control?
At or close to the cylinder
How are packing rings supposed to be cut?
At an angle leaving no gaps in the ring.
One of the oldest and most widely used seal is what?
Stuffing box
Where does the lantern ring need To be positioned?
Directly under the Inlet port
The most common type of non positive displacement pump…
Centrifugal
Centrifugal pumps may be classified as what?
Volute and diffuser both can be single or multistage
What is injected into the stuffing box?
Flush water
3 things that flush water does?
- Cools shaft
- Keeps the packing moist
- Flushes contaminants
2 impeller configurations?
Over hung and between the bearings
2 types of seals?
Compression packing and mechanical seal
3 types of impeller styles?
Enclosed, semi open and open
What are the components of a stuffing box?
Gland follower
Rings of packing
Lantern ring
What is the meaning of head?
Height of a liquid
Two systems of pressure specification are used in pumps such as?
Psi and head
3 things that determine the capacity of a pump?
- Size of impeller
- Speed of impeller
- Viscosity of liquid
Formula to find pressure?
Head x .433 x 1
A positive pressure at the pump Inlet?
Positive head
Discharge head is the pressure of the…
Discharge
The distance which the pump lifts the liquid,
Total head
Distance that the liquid must be lifted to the pump?
Negative head
What are the 2 types of positive displacement pumps?
Rotary and reciprocating
Reciprocating and rotary pumps can either be what 2 types?
Fixed or variable displacement
Diaphram and piston pumps are considered what type of pump?
Reciprocating
Gear and vane pumps are considered what type of pump?
Rotary
What are the 3 components inside of vane pumps?
Ring, vane and rotor
What are the 2 types of positive displacement pump mounts?
Frame mounted and C frame mounted
Disadvantage of a frame mounted pump?
Motor and pump must be aligned
A fixed displacement pump must have what to limit system pressure?
Relief valve
A variable displacement pump uses a relief valve to back up what?
Pressure compensator
What does the compensator do?
Controls system pressure
How do you control pressure in a fixed displacement pump?
Divert off excess flow
How do you control pressure In a variable displacement pump?
Stop flow at the pump
Purpose of a relief valve?
Limits system pressure
3 things that cause true pump cavitation?
- Cold oil
- Restriction on the Inlet
- Suction lift rating
What causes pseudo cavitation?
Air leak on the Inlet side and not maintaining oil levels
How to tell you’re dealing with pseudo cavitation?
Foamy hydraulic fluid in the tank
Definition on cavitation?
Formation and collapse of Air bubbles in the pump
Most common type of non positive displacement pump?
Centrifugal
2 types of positive displacement pumps?
Fixed and variable displacement
Types of fixed displacement pumps
Gear pumps, vane pumps, piston pumps, diaphragm pumps
Types of variable displacement pumps?
Piston pump and vane pump
Without a change in volume in a pump….
No fluid will flow through
Definition of a pumps capacity?
The amount of fluid a pump can move in a given time
What is a pumps flow measured in?
GPM (gallons per minute)
What 3 things determine a pumps capacity?
- Size of pumping element
- Viscosity of fluid
- Rpm
What are 2 ways pressure can be controlled?
- At the pump (pressure compensator)
- Deviate off unneeded flow (relief valve)
How to know which side is the Inlet and outlet of the pump?
Inlet is the bigger size and the outlet is the smaller size
Definition of pump cavitation?
The formation and collapse of air bubbles
What are some things that would make a pump cavitate?
Blockage on the Inlet or the viscosity of fluid in the pump
What is the other type of pump cavitation?
Pseudo cavitation
If pseudo cavitation is taking place, how may the system be running?
Spongey
Reasons for pseudo cavitation?
Leak on the Inlet side of the pump, excess air in the system, tank level too low
What would be a good indicator of pseudo cavitation?
The fluid in the tank would be foamy
4 ways valves are actuated?
- Manually
- Mechanically
- Electrically
- Pilot pressure
4 center conditions for DCV’s?
- Blocked
- Tandem
- Float
- Open
3 uses for an accumulator?
- Absorb shock
- Maintain pressure
- Establish flow
What does cracking pressure mean?
When a valve opens prematurely
What does a sequence valve do?
Allows one thing to happen before the other. To have reverse flow you must have a bypass check valve.
What does a pressure reducing value do?
Normally passing, once downstream flow reaches the valve pressure, the valve become non passing and fluid stops flowing
What does a counter balance valve do?
Counter acts a weight on a cylinder
What is the job of a relief valve and how do you trouble shoot it?
To limit system pressure and to make sure it starts flowing at the set point
What percentage of hydraulic fluid is air?
10% air by volume
