week 4 pneumatics Flashcards
flared fittings are not used where in pneumatics?
where vibration is present.
how do you tighten a flare nut?
finger tight, then for nuts under 5/8 use a flare tubing wrench for a 1/4 turn and over 5/8 diameter use 1/8 of a turn.
how do you tighten flareless fittings?
hand tight then 1/6 to 1/3 more with a wrench.
true or false use the bursting pressure to select a hose
false, always use the working pressure.
how are pressures measured for pressure hoses?
standard in psi, metric in MPA. mega pascals 1 MPA = 145 psi
how are vacuum hoses rated?
inches of mercury
how is hose size measured?
by inside diameter, which determines the velocityof the fluid that flows through it.
on what is the diameter of tubing based?
the outside diameter
which type of tubing is best suited to flared fittings?
thin walled tube
which type of tubing are flareless fittings most suited for?
thick wall tube
how is the wall thickness of tubing specified in the imperial system?
the wall thickness is in thousandths of an inch.
what is the most important property of the material of the inner tube in a hose?
compatibility with the fluid
which part of a hose determines its pressure rating?
the reinforcing
which type of hose should should you use on the inlet to a pump?
vacuum hose
what does a excess flow valve do?
the valve is normally open, but excess flow surges push the poppet against a spring, causing flow to be cut off.
what is the purpose of the safety relief valve?
to bleed off excess system pressure before it becomes to extreme.
possible causes of why an actuator cylinder is drifting…
the piston seal is leaking.
the operating valve is leaking.
the lines are leaking.
possible reasons why the cylinder is sticking or binding
the packing on the cylinder rod is over-tighten.
the cylinder is misaligned.
the seals are defective.
the pilot pressure is low.
possible causes why the cylinder body deal is leaking
the tie rods are loose.
the pressure at the cylinder is excessive.
the cylinder body seal is pinched or extruded.
possible causes why the rod gland seal is leaking
the seal is deteriorating
possible causes why a pneumatic valve is blowing to exhaust when actuated.
the valves seals are faulty.
the valve-to-base gasket is faulty.
the spool is damaged
possible cause why a pneumatic valve is blowing to exhaust when not actuated
the inlet poppet is not sealing.
possible causes why the pilot section is blowing exhaust
the pilot cover is loose.
the poopet is not sealing
possible cause why the poppet is chattering
the air supply pressure is too low.
the pilot pressure or signal pressure is too low.
in pneumatic systems environmental pollution occurs in what two forms mostly?
noise and oil mists
in operating pneumatic cylinders under clamping conditions the system should be designed to avoid accidental operation through the use of what
control interlocks or manually operated switching devices with protective covers
to avoid hand injuries caused by pneumatic clamping conditions what precautions should you use
pressure transducers or sequence valves to ensure the second operation does not occur until the clamping is confirmed.
where should air intake occur on a pnuematic system?
coolest place possible
air recievers are classified as
unfired pressure vessel
what must a pressure vessel have
gauge, drain, safety relief valve, fusible plug,
air reservoirs have two functions, what are they
first to accommodate any fluctuations in the system’s supply. this dampens pulsations and creates a steady pressure to the system.
second to reduce the velocity of the air, this allows moisture to settle out.
what are the three most common piping systems for compressor systems?
the grid (dead end or trunk), the decentralized, the loop system.
if an FRL is installed backwards what would happen?
the lubber would clog the regulator and the filter would remove the oil
all air hoses larger than what should be equipped with excess flow vavles to limit pressure in the event of fitting or hose failures.
1/2 inch
Name three factors to affect control of speed in pneumatic systems
Uniformity of the applied load Friction forces Acceleration forces
Name an example of 2/2 valve?
Air tools trigger.
Name an example where 3/2 valves are used?
Single acting cylinder
Name what examples a 4/2 dcv is used in
Reversible motion of a cylinder
What are 4/3 valves used in?
Reversible motion cylinder with a center position, that always a float or exhaust to happen in the center position.
What is the difference between the operation of a 4/2 dcv and a 5/2 valve
The dcv on a 5/2 allows exhaust.
5/3 dcv have what common center positions?
Block, exhaust, pressure, tandem.
Explain shuttle valve
A shuttle moves back and forth to allow flow in one Direction compared to the pressure highest.
Name three type of flow control valves?
Ball, globe, needle. Needle being the most common.
What are causes of low air pressure in the receiver?
Leaky compressor valves, stuck piston rings, faulty unloading valve, break in the line.
You have excessive air pressure in the receiver what could cause this?
Faulty unloading valve, faulty safety valve.
Your pneumatic circuit has low air pressure why
Pressure regulator sweet too low Damaged line
Your pneumatic circuit has excessive pressure why?
Pressure regulator set too high
Your pneumatic circuit has sticky valves why?
Excessive carbon deposits on the valve components, insufficient lubrication, valve packing to tight.
Your pneumatic circuit has incorrect delivery of lubrication why?
Excessive oil discharge, no oil discharge.
Your pneumatic circuit has a cylinder moving inconsistently why
Scored piston or liner, bent piston rod, damaged piston seals, insufficient air pressure
Your pneumatic circuit has a motor moving inconsistently why
Scored rotor casing, worn bearing, insufficient air pressure.
Name three devices to measure vacuum
Barometer, manometer, bourdon tubes.
name four ways to contol maximum pressure
unloading devices, throttling the air intake, using variable speed drive, using a pressure switch.
in a fingers unloading device the finger is control by what
the pilot air provided the compressor output
when using a variable speed drive such as a gas or diesel engine power unit your doe this control maxiumum pressure from the compressor?
by having the centrifugal clutch disengaging, allowing the engine to run at low rpm with no load.
oil is not add to the compressor intake air why
because the overheating of the oil would take away the lub properties.
what is this symbol?
lubricator
what is this symbol?
cooler
what is this symbol?
filter
what is this symbol?
water seperator, manual drain
what is this symbol?
water seperator, auto drain
what is this symbol?
cooler without representation of the flow lines of the coolant
what is this symbol?
cooler indicating the flow lines of the coolant
what is this symbol?
pressurized reservoir
what is this symbol?
air dryer
what is this symbol?
filter with a manually drained water trap
what is this symbol?
filter with an auto drain water trap
what is this symbol?
pressure regulator
what is this symbol?
pressure regulator with gauge
what is this symbol?
frl
what is this symbol?
compressor
what is this symbol?
check valve
what is this symbol?
check valve with spring return
what is this symbol?
variable flow control
what is this symbol?
one way flow control valve
what is this symbol?
silencer
what is this symbol?
shuttle valve
what is this symbol?
quick exhaust iso
what is this symbol?
quick exhaust ansi
what is this
3 port 2 positions
what is this
four port two positions
what is this
4 port 3 positions
what is this
5 ports 3 positions center blocked
what is this
5 port 3 positions exhaust center
what is this
5 port 3 position pressure center
What are the general difference between pneumatic systems and hydraulic systems?
- fluid medium used is commonly air (which can be compressed)
- the supply is atmosphere
What laws and theories can be applied to both pneumatics and hydraulics?
- Pascal’s Law
- Bernoulli’s Principles
- Law of Conservation of Energy
Describe absolute zero temperature
- no molecular movement occurs
- 0 value in terms of Rankine and Kelvin Scale, equalling -460*F and -273*C
Describe absolute zero pressure
- there is no pressure - 0 PSIA
What is the normal atmospheric pressure at sea level?
- 14.7 PSIA
- Standard Air = 14.7 PSIA @ 68*F - 30% humidity
- Free Air = air at the location of intake
Why are psia and psig?
- 14.7 PSIA = 0 PSIG
How is vacuum measured?
- measured with a barometer
- measured in mm HG or “HG
What are the properties of characteristics of compressed air?
- it can be compressed or reduced in volume
- air will expand to fill any container
- pressure in a confined, static (at rest) fluid acts the same and equally in every direction. It always acts at right angles to the containing surface (Pascals Law)
- there must be a pressure change to create air flow
- air flows from high- to low-pressure areas
What are the ways of increasing pressure in a sealed container?
- reducing the volume to create more impact on a smaller wall area
- introducing more air into the confined space
- heating the air so the molecules travel faster and increase the intensity and amount of impact on the same wall area
Which is a more efficient transfer of energy: laminar or turbulent flow?
- laminar flow
What is …
- Boyle’s law?
- at constant temperature, absolute pressure (P) varies inversely to the volume (V)
- P1V1 = P2V2
What is …
- Charles law?
- at a constant pressure, the volume (V) of a gas varies proportionately to its absolute temperature (T)
- V1/T1 = V2/T2
- for a constant volume of a gas, the pressure (P) varies proportionately to its absolute temperature (T)
- P1/T1 = P2/T2
What is …
- the Ideal Gas law?
- Boyle’s and Charle’s laws combined
- P1V1/T1 = P2V2/T2
- P1V1T2 = P2V2T1
How are the vacuum pumps used to create fluid power?
- removes the air rather than compressing it
- pressure differential induces a “HG rating
What treatments are necessary to ensure the quality of air is suitable for a pneumatic system?
- ensures that the air is not harmful to the system; protecting against contamination, moisture and heat
- air treatment consists of:
- filtering
- cooling
- removing moisture and oil
- storage
What does the air-intake filter control?
- control the amount of airborne contaminants allowed to enter the compressor
- amount of filtration dependent on requirement of the compressor
- first line of protection
What do intercoolers control?
- heat generated due to compression
- used to cool the air between stages
- air-cooled intercoolers use a fan to force air over finned tubes through which compressed air passes. The fins and tubing must be kept clean for efficient heat dissipation
- liquid-cooled intercoolers use a nest of tubes immersed in recirculating liquid. Shell and tube heat exchanger.
Define dew point
- temperature at which water condenses as it is cooled
- water vapour in compressed air settles out as free water if the intercooler temperature falls below the dew point.
Describe the location and purposes of water traps
- vital components in the removal of water from system
- can be placed in many locations to expel large amounts of water from the lines - wherever the compressed air is cooled and may fall below its dew point, a water trap is installed
- common areas are at/after the:
- intercoolers
- aftercoolers
- air dryers
Describe the purposes and principles of the operation of aftercoolers
- vital components in the removal of water from system
- can be placed in many locations to expel large amounts of water from the lines - wherever the compressed air is cooled and may fall below its dew point, a water trap is installed
- common areas are at/after the:
- intercoolers
- aftercoolers
- air dryers
Describe the purposes and principles of the operation of aftercoolers
- heat exchangers which cool the air after it leaves the compressor and before it enters the receiver
- receivers can also act as an aftercooler
- aftercoolers permits the removal of most of the moisture and other entrained liquids which may be in the compressed air during the compression stages
- work on the principles of a shell and tube heat exchanger, with cooling happening due to counterflow of a air- or water-cooled aftercooling passing by compressed airlines
- moisture is collected and drained out of the system by manual or automatic water traps.
What are the functions of an air receiver?
- a storage tank for the compressed air before it enters the system
- acts as a reservoir to accommodate any fluctuations in the systems supply. This dampens pulsations from the compressor and provides a steady pressure to the system
- also reduces the velocity of the air. This allows any moisture carried over from the aftercooler to settle out. If an aftercooler is not used, the receiver acts as the aftercooler
How is an air receiver classified?
- an unfired pressure vessel (potentially explosive)
Where is the maximum pressure control located on a pneumatic system?
- located in, or on, the compressor, NOT the air receiver
- maximum working air pressure is never higher than the maximum working pressure stamped on the receiver
What does the safety valve on the air receiver control?
- the safety valve on the air receiver is used in case of any failure in the system
- releases any excessive pressure, due to the failure of the unloading valve or ta a pressure surge transmitted back from the system
- usually set 5-10% above the systems maximum pressure
Where is the drain valve located on the receiver?
- must be installed at the lowest point on the receiver
- care must be taken to ensure the drain valve can drain the tank completely
- water and oil emulsions which settle out should be drained off by this valve regularly
What is the purpose of a fusible plug?
- will melt and release all the pressure in the receiver if the air temperature becomes dangerously high
- ensure the path in which the pressure would vent will not endanger workers nearby
How is the pressure in the receiver monitored?
- an air pressure gauge monitors the pressure inside the receiver
What are two types of compressed air used in industry?
- instrument air
- must be clean, dry and free of oil
- plant air
- should be clean and have a low moisture and oil content
Describe the operating principles of the following:
- deliquescent dryers
- contain chemical desiccants, which absorb moisture
- the desiccants are consumed in the drying process, which means the chemicals must be replenished periodically and their disposal may be a problem
Describe the operating principles of the following:
- regenerative desiccant dryers
- use a solid desiccant which absorbs water onto its surface
- usually silica gel, activated alumina, or a molecular sieve
- use two identical chambers in which the air is dried
- as one chamber becomes saturated, flow is directed to the other, and the saturated chamber is dried out
- heat may be applied to speed up the drying process, but the chamber must be cooled before it is ready to use again
- heat 75% - cool 25%
Describe the operating principles of the following:
- refrigeration dryers
- condense moisture from compressed air by cooling the air in heat exchangers chilled by refrigerants
- moisture collects in a moisture trap and is drained
- the compressed air is then reheated to operating temperature before it enters the system, in order to prevent condensation from forming downstream from the drye
Describe the operating principles of the following:
- membrane dryers
- gas separation devices
- consist of permeable membrane surfaces that block nitrogen and oxygen molecules(air), but allow water vapour molecules to pass through
- because the membrane vents gas, not condensate, there is no need for regeneration or fear of freezing
- have no moving parts to wear out
- non-electric and suitable for most hazardous environments
- housing is constructed from plastic and aluminum to prevent corrosion
How is contamination produced within a compressed air system?
- construction, assembly, and maintenance debris
- oil carried over from the compressor
- operational wear particles, pipe scale, and rust generated within the line
Describe the operating principles of a typical filter that removes water, oil and particulate matter from compressed air
1 - a deflector plate swirls the air around the filter bowl
2 - a shroud ensures that the swirling action occurs around the filter bowl and not the filtering element
3 - this causes the larger particles and excess moisture to be thrown out the side of the filter bowl
4 - a baffle below the filtering element creates a quiet zone which allows the particles and moisture to collect and prevents them from becoming entrained in the air flow again
5 - the air is the forced through the filtering element which removes the smaller particles
6 - clean air then exits the filter and enters the system
What is the difference in filtering action between standard and coalescing filters?
- standard filters
- filter solid particles and collect any excessive moisture that happens to condensate at that time
- coalescing filters
- designed to remove all solid particles as small as 0.3 microns, together with nearly 100% of the oil and water vapours, from the air
- they use a desiccant similar to the desiccant in air dryers
Describe the purpose and operating principles of the following:
- pressure regulator
- reduces the line pressure
- consist of a main piston or diaphragm which controls a poppet or valve by means of a connecting pin
1 - an adjusting screw preloads a spring on top of the piston
2 - the pilot passage is open to the outlet port
3 - as the down-side pressure increases, the piston rises, along with the poppet, and the flow decreases
4 - a pressure gauge is mounted on the down-side of the regulator so that any adjustment of the regulator can be read directly
Describe the purpose and operating principles of the following:
- lubricator
Air lubricators supply clean oil into the line to be carried to the components.
- As the air enters the lubricator, a predetennined amount is allowed through the venturi.
- The remaining air is let through a bypass valve into the bowl and out the outlet port.
- The air pressure in the bowl forces the oil up the capillary tube which supplies oil to the venturi. As the air passes through the venturi it creates a low-pressure area which ailows the oil to enter the airstream.
- A feed-rate adjustment allows for the desired amount of oil to enter the airstream. Only a few drips of oil a minute are needed for most air lubrication systems.
- As oil enters the airstream, it is atomized into an airborne oil mist or fog which is carried to the pneumatic device.
- A sight glass allows for a visual inspection of the flow-rate of the oil.
What is a FRL conditioning unit?
Air filters, regulators and lubricators are frequently preassembled and called
FRLs.
What system functions do pneumatics valves control?
Reducing valves (pressure regulators) reduce the pressure of branch lines for specific applications. Directional control valves (DeVs) control the movement of the actuator(s). Flow control valves control the volume (and therefore speed) of air to the actuator.
Compare pneumatic valves to hydraulic valves
- the method in which the spools are sealed
- the release of exhaust air into the atmosphere. The exhaust air is released at the valve, at the actuator, or, in a remote area, through a conductor.
Describe the methods of sealing spool valves
- In the packed bore design. the O-rings are fixed in grooves in the body through which the spool slides.
- In the packed spool design the O-rings are fixed in the spool.
The lapped spool design is another method which has the mating surfaces lapped to precise tolerances. This design relies on the lubrication between the mating surfaces to do the sealing.
What precautions should be exercised when using a manual override?
Caution! Before using a manual override, ensure that:
- The equipment is safe to operate.
- Everyone associated with the equipment is aware that the machine may
operate. They should stand clear of any moving parts.
Which device produces more infinite control: solenoid-controlled DCV or pilot-operated DCV?
pilot-operated DCV
Describe the purpose and/or principles of operation of the following:
- flow control valve
Flow control valves restrict the flow rate in a leg of a pneumatic system.
Check valve remains held against seat as air passes by an Adjustable orifice.
In free flow a Light spring is compressed allowing air to pass by unhindered.
Describe the purpose and/or principles of operation of the following:
- quick exhaust
When a cylinder is required to return rapidly, a quick exhaust valve is installed in the retract line of the cylinder. This allows the air to exhaust right at the cylinder instead of returning through the DCV to exhaust.
Describe the purpose and/or principles of operation of the following:
- shuttle valve
A shuttle (self-activated) valve is used when it is necessary to have two DCV s operating a single actuator. This valve shifts to allow either of the DCV to activate the actuator but only one at a time.
Describe the purpose and/or principles of operation of the following:
- muffler
Compressed air exiting an open conductor may generate high intensity sound. A muffler breaks up the sound waves and smooths them out, reducing their energy.
a series of passageways through which the air must travel in order to exit through a pneumatic muffler.
Compare pneumatic actuators to hydraulic actuators
Pneumatic actuators (cylinders and motors) are of the same design, style, and action as hydraulic actuators. The difference between the pneumatic and hydraulic actuators is that many pneumatic actuators use corrosion-resistant materials (aluminum, brass and stainless steel) in their construction. Due to the lower pressures, they may use seals with lower capacities.
Compare pneumatic conductors and fittings to hydraulic conductors and fittings
Pneumatic systems use conductors in the same manner as hydraulic systems. Due to the lower pressure (below 200 psi) and potential moisture in the lines, pneumatic conductors are often made of brass, copper, aluminum, plastic and other corrosion-resistant materials. Seamless steel (black) pipe is also used because of its low cost but corrosion can occur more rapidly. The end fittings, pipe, and tubing dimensions for pneumatic conductors are the same as those for hydraulic conductors.
What prevents the hose from collapsing with flareless fittings?
When these fittings are required, ensure that an internal tube support is used to prevent the hose from collapsing.,
Describe quick-disconnect couplers
Pneumatic quick-disconnect couplers have a shut-off in the recessed half and an open passage in the protruding half. These are single shut-off as opposed to the double shut-off of a hydraulic quick-disconnect coupler.
Describe the following piping systems:
- grid system
The grid (dead end) system is the simplest and least expensive system. It consists of a main line from the compressor which begins large and becomes progressively smaller in diameter as it reaches the end. Feeder lines of uniform size provide outlets at convenient locations. The problem which arises with this system is that the work stations at the end of the system may have insufficient air supply (air starvation) when demands are heavy.
Describe the following piping systems:
- decentralized system
The decentralized (unit) system consists of two or more grids within the main system, each with its own compressor. This arrangement allows for shorter supply lines which results in more uniform air supply and system pressure. This system is also more versatile and adapts easily to changing requirements.
Describe the following piping systems:
- loop system
The loop system consists of two or more compressors around a continuous loop. This arrangement provides a parallel path to all work stations. This system allows the air to move continuously around the system, in either direction, to supply the work stations. This tends to be the preferred system.
How is moisture prevented from accumulating in the lines?
Permanent pneumatic lines are installed in such a manner that any moisture accumulating in the line flows toward a drain. Air-drop lines can be placed anywhere along the main line to feed air to working compnnents. An air-drop line is installed witii a tee junction (a tee-off) that goes up and then down to its work area. This causes any moisture to flow past the tee to the drain and not into the air-drop line. A water leg must be installed at the end of the main line to accumulate and drain any excess moisture.
Describe the operation of a quick-exhaust valve and state where it is placed
Quick exhaust circuits are used where very rapid actuator speed is required. A quick-exhaust valve is coupled between the cyliuder’s head end and
the DCV. Because the piston must extend very rapidly, the exhaust air is allowed to escape near the cylinder instead of returning through the DCV. The retraction stroke is not required to move as quickly, so the path through the DCV is adequate.
What parts tend to freeze in cold weather in a compressed air circuit?
When work area temperatures go below freezing. valves tend to freeze up. This is due to the cooling action created by air expanding in a pressure drop through the ports.
How are these parts thawed out and prevented from freezing again?
- installing an infra-red lamp or heat source on the valve
- introducing a small amount of permanent anti-freeze into the lubricator-this takes care of the whole system
- using an anti-freezer to put alcohol into the airlines-this also takes care of the whole system
- heating the air supply-usually done in a steam mill by running a steam line next to or even through the air line
- maintaining the building or work area temperature above freezing.
