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2nd 2020 > Pneumatics > Flashcards

Pneumatics Flashcards

1
Q

How is force exerted in a pneumatic system?

A

Force is exerted through compressed air.

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2
Q

What is mass and inertia?

A

Mass is in all objects and represents the amount of matter in an object. Its what gives objects weight.
Inertia represents the objects resistance to movement and the force needed to move the object.

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3
Q

What is pressure and how do you find its value?

A

Pressure is the amount of force (lbs) exerted on an object or substance, divided by the area (square inches) over which the force is exerted. PSI is the most common measure of pressure.

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4
Q

What is absolute pressure and how is it measured.

A

Absolute pressure is gauge pressure plus the atmospheric pressure (14.7 psi)
Psig-125
Psia- 139.7

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5
Q

What is work and what is the equation for it?

A

Work is accomplished when a force moves an object a distance. It is expressed in foot- lbs or inch lbs. Power can then be found with P=W/T

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6
Q

How do you find force in a pneumatic system?

A 
Force= pressure x piston area
F=  ( lbs / in^2) x in^2  the answer will be in pounds.
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7
Q

What is dispersion and diffusion?

A

Diffusion is the rapid intermingling of the molecules of gases together. They can never be restored once lost to the atmosphere. Ex. R-134 from car ac system being released through the valve instead of removing with vacuum pump.

Dispersion is the temporary mixing of liquid with gases similar to moisture and oil in the air of a compressor. It can be removed most of the time.

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8
Q

What is Pascal’s Law?

A

It states that when a gas is confined in a container, its pressure is equally distributed in all directions.

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9
Q

What is Boyles Law?

A

It states that if temperature and amount of gas is constant, the pressure of the gas varies inversely with its volume.

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10
Q

What is Charles’ law?

A

If the volume of a confined quantity of gas remains constant, the change in the pressure of the gas varies directly with a change in the absolute temperature

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11
Q

What is Pneumatic Leverage?

A

The ability of a force can be multiplied from a small driver to a larger one, along with this force exchange comes an inverse effect of the amount of travel. That is, for every force increase, there is a corresponding movement decrease. The ratio for pressure increase is inversely related to travel distance.

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12
Q

What is Streamline or Laminar Flow?

A

It is the ideal type of airflow in a pneumatic system because the air layers move in parallel lines.

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13
Q

What is Turbulent flow?

A

When the passage is too small for the desired flow velocity of the earth. The density and viscosity of the air also affect the turbulent flow, but not as much as the flow passage and the flow velocity.

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14
Q

What is Bernoulli’s Law?

A

In a newmatoc system there are two types of energy, kinetic and potential, kinetic energy is the moving air, potential is the result of the air pressure. it states that if air velocity increases,the kinetic energy of the air also increases, while the total energy ( Potential + Kinetic ) of the air remains constant.

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15
Q

The viscosity of the air is the measure if the air’s?

A

It is the resistance to flow because it is the measure of the airs internal friction. The viscosity of air is referred to as dynamic viscosity.

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16
Q

What are positive- displacement compressors?

A

They are capable of compressing air to very high pressures. These may be risiplicating piston, rotary sliding vain, helical screw, liquid piston, impeller, or diaphragm- type.

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17
Q

How does a reciprocating compressor work?

A

As the piston retracts it creates negative pressure and opens the intake valve. As it returns the intake valves close, when the stroke is almost complete the discharge valve opens. At this point the air is compressed and is moved to the tank.

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18
Q

What is the purpose of a inter cooler?

A

To reduce the horse power needed to run a motor for a compressor. This is why multi stage compressors are more efficient. The air is cooled between stages.

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19
Q

What is a shell and tube heat exchanger?

A

It is a heat exchanger consisting of a bundle of tunes mounted in a shell. Cooling water is passed through the shell in the opposite direction, compressed air flows through the tube, or vice-verca. In whatever arrangement known as counter flow.

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20
Q

What are the two classifications of air compressors?

A

Positive displacement - confine the air within a closed space and compress it by decreasing the volume.

Dynamic - accelerate the air with rapidly turning blades. This increase in air flow causes the air pressure to raise.

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21
Q

What are the two classifications of air compressors?

A

Positive displacement - can find the air within a close space and compress it by decreasing the volume.

Dynamic - accelerate the air with rapidly turning blades. This increase in air flow causes the air pressure to raise.

22
Q

What are the two primary functions of compressor lubricating oil?

A

To reduce friction of the moving parts and to improve cooling or the transfer of heat in the compressor.

23
Q

What must be done on a large compressor before starting?

A

It must be unloaded or relieved of all internal pressure so that it does not compress air at first and is easy to start. When the compressor is turning at sufficient speed, the unloading controls are denergized allowing the compressor to load up and compress air.

24
Q

How much PSI can a single stage sliding vain compressor make?

A

Up to 50 PSI. If higher pressure is needed, a two stage model is used, capable of up to 125 PSI. Also furnished with an intern cooler. Smaller than piston compressors and the efficiency is also lower.

25
Q

Basic Parts of a rotary screw compressor?

A

They are constructed with 2 rotors 1 with a concave profile and the other with a convex profile.

26
Q

What speeds do screw compressors opporate at?

A

Between 3000 and 12000 rpm

27
Q

What are the Characteristics of the impeller compressor?

A

They are low pressure high volume compressors, often referred to as blowers. Made up of a housing and two interlocking, timed, gear driven impellers. Operates similar to a gear pump.

28
Q

Impeller compressor applications and what are the advantages?

A

They handle large volumes of air at lower pressures they require no lubrication because the impellers do not touch each other. Also the air temperature does not increase much, therefore it requires little or no cooling.

29
Q

What are the disadvantages of a centrifugal air pump?

A

They require more hp per cfm than other compressors

They operate at very high speeds.

30
Q

How do you control a centrifugal compressor output?

A

Speed variation

Suction Throttling

Discharge Throttling

Recirculation

The most efficient method of the four is speed variation. One downside is that many compressors lose efficiency when the speed drops below normal speeds.

31
Q

What affects the amount of water vapour that can be held by air?

A

The pressure the air is subjected to. As air pressure increases the ability to retain or hold moisture decreases. If the temperature increases with pressure the then the ability to retain water increases.

32
Q

How do you remove water and oil from compressed air?

A

When is the most common ways is to condense the water vapor so that it can easily be removed. Another way is by circulating the air through a dryer, which removes the water vapor from the air without condensing it.

33
Q

What’s the best way to cool medium sized, single stage compressors?

A

Water cooling is the most economical when operating more than 8 hours A-day, and for larger compressors or any that operate more than 10 hours A-day. Air cooling usually reserved for smaller to medium sized compressors with 2 stages that operate less than 8 hours A-day.

34
Q

What are the 2 types of air dryers ?

A

Deliquescent type-aka chemical type is a canister with a moisture retaining substance inside similar to silca to preserve freshness in food. As it absorbs moisture it slowly dissolves and becomes a liquid itself or deliquesce. Next it would then gravity feed to a drain petcock.
Absorption- utilizes two tanks, one dries the air while other regenerates or heats up the bed of dessicant, melting the impurities off the surface. Based on the physical attraction moisture and unsaturated dissicants have for eachother.

35
Q

What is an air receivers purpose?

A

To store the compressed air made by the compressor. When selecting it must be rated high enough to keep up with system demands. There will always be times are the compressor might not be able to keep up with demand. During these peak flow times air in the lines and in the tank supply the load or from dropping too low.

36
Q

Whats the best way to achieve contaminant separation in secondary air treatment?

A

The best way is centrifugal separation. When rapidly moving air is swirled in a circular path throwing the particles outward. They are also known as initerial separators because they depend on the initeria of a heavy moving particle to aid in separation. Inertial separators are not always centrifugal, sometimes they utilize changing of direction of air rapidly while in the filter, shaking loose the bigger contaminants. They are mainly used as pre-filters to pick up large dirt particals.

37
Q

What are the very fine oil particals found in compressed air?

A

They are called aerosols and they can not be separated by ordinary means or by after cooling.

38
Q

What are nominal and absolute ratings?

A

Nominal rating is based on its ability to stop a percentage of particals of a given size. If it stops 100% of a particle size it is referred to as its absolute rating.

39
Q

What are wetted filters?

A

Wetted filters utilize a coating of oil to help collect and hold contaminants from the air. Have higher initial costs than dry filters, but they can be cleaned many times.

40
Q

What are fine lubricators?

A

They provide a fine suspended oil mist in the airstream, this way more positive lubrication is available at greater distances from the lubrication. Especially efficient with complicated piping systems and intermittent equipment operation.

41
Q

What type of flow in a pipe results from too much velocity or restrictions?

A

You get turbulent flow, it wastes energy by creating heat. To avoid, inner walls of air line should be smooth and not have unnecessary changes in direction.

42
Q

What affects the amount of pressure loss in a pipe?

A

Air flow volume
Air pressure
The lower the pressure, the greater the ratio between the pressure loss and the optimal pressure level. These pressure losses occur because airflow at lower pressures is affected more by friction with the walls of the piping than is airflow at higher pressures.

43
Q

How much should piping slope when installed horizontally?

A

When installed as compressor discharge and distribution lines, they should have a 1” for every 10’ of pipe

44
Q

Should pipe dope always be used?

A

Yes it should always be used. Used sparingly and never on thread ends.

45
Q

What one way control valves are identified?

A

One way to distinguish is by the amount of connecting ports. 4 way valves sometimes have 5 ports with the 5th being a second exhaust.

46
Q

What is a needle valve?

A

It is a two way valve and is excellent for very high pressure applications and at throttling or flow reducing valve.

47
Q

Describe control spool valves?

A

It is the most widely used, easy to operate, even with high pressures because the internal force balance itself. Can be made to shift to more than one position.

48
Q

Why are 4 way valves commonly used in pneumatic aystems?

A

asters? Are used because they have more functions and are more versatile. They simplify pneumatic controls and reduce the amount of controls in the system contrary to belief.

49
Q

What is cracking pressure?

A

It is the pressure at which a poppet style relief valve initially opens.its determined by the adjustment of the spring?

50
Q

Describe diaphragm relief valves.

A

Used on larger flows and have a smoother relief action. Because the compressed air works on a larger pressure sensitive area than in poppet valves.

51
Q

What is a pressure relief valve?

A

In place to blow off excess pressure build up. Protect the system and their components from damage in the event of excess pressure

2nd 2020 (10 decks)

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