3B2 E2.5 C8 Review

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Questions and Answers

What is the definition of Compression Ratio?

The ratio of the volume at the beginning of a compression stroke to the volume at the end (correct)

The final discharge pressure of a compressor

The volume swept out by the piston of a reciprocating compressor

The quantity of air compressed and delivered in a given time period

What does the term 'Capacity' refer to in a compressor?

The final discharge temperature of the compressor

The type of gas the compressor receives

The number of cylinders used for compression

The volume of atmospheric air compressed in one minute (correct)

Why is staging used in compressors?

To increase the final discharge temperature

To decrease the compression ratio in each cylinder (correct)

To decrease the compressor displacement

To reduce the volumetric efficiency

What is Compressor Displacement a measure of?

The volume swept out by the piston of a reciprocating compressor Signup and view all the answers

How is Capacity expressed in compressors?

Cubic meters per minute of free air Signup and view all the answers

What is the purpose of using two or more cylinders in a compressor?

To progressively increase the pressure in stages Signup and view all the answers

What is the primary purpose of using intercoolers in a multi-stage compressor?

Increase the efficiency of the subsequent compressor stage Signup and view all the answers

Under what conditions will moisture condense out of the air after intercooling?

When the air is sub-cooled below the pressure dewpoint Signup and view all the answers

What is the primary purpose of using an aftercooler in a compressor system?

Facilitate the removal of moisture and oil vapour from the compressed air stream Signup and view all the answers

What is the effect of installing a compressor at a high altitude on the compression ratio and air delivery?

The compression ratio will increase, and the air delivery will decrease Signup and view all the answers

How does carrying moisture in the compressed air affect air-operated instruments and tools?

It has a detrimental effect on their performance Signup and view all the answers

How much moisture does saturated air, at normal temperature and atmospheric pressure, contain for every 28 m3 of air?

0.5 kg Signup and view all the answers

What does the compression ratio of a compressor represent?

The ratio of gas volumes at the beginning and end of compression Signup and view all the answers

What is the primary benefit of using multiple stages in a compressor?

Improved volumetric efficiency Signup and view all the answers

Which term is used to quantify the volume of atmospheric air compressed in one minute?

Capacity or F.A.D. Signup and view all the answers

In a compressor system, what does the term 'free air' refer to?

Atmospheric air at normal pressure Signup and view all the answers

What does compressor displacement measure in a reciprocating compressor?

The volume of atmospheric air compressed per cycle Signup and view all the answers

What is the purpose of cooling the air between stages in a multi-stage compressor?

To increase volumetric efficiency Signup and view all the answers

What is the primary purpose of an intercooler between stages of a multi-stage compressor?

To improve the density of the air, which improves the efficiency of the subsequent compressor stage Signup and view all the answers

How much does the atmospheric pressure decrease as the altitude increases?

Atmospheric pressure decreases as altitude increases Signup and view all the answers

What is the consequence of not removing oil vapor from the compressed air stream?

Negative effect on air-operated instruments and a risk of ignition or explosion Signup and view all the answers

Which statement best explains the impact of moisture on the compressor system?

Moisture condenses out of the air during compression, and if not removed, negatively impacts the performance of air-operated instruments and tools Signup and view all the answers

Why is the displacement of a multi-stage compressor determined by the first stage piston only?

Because the same air passes through all stages in series Signup and view all the answers

How does the operation of a compressor at a high altitude affect its performance?

A compressor at high altitude requires a higher compression ratio to produce the same discharge pressure as a machine at sea level, and delivers less mass of air Signup and view all the answers

What is the primary purpose of a suction valve in a compressor?

to draw air into the cylinder Signup and view all the answers

What is the advantage of using multiple cylinders in a compressor?

to increase capacity and smooth out discharge pressure Signup and view all the answers

What is the function of an oil screen in a compressor?

to filter out contaminants from the oil Signup and view all the answers

What is the purpose of a crankcase door in a compressor?

to provide access to the crankcase Signup and view all the answers

In a two-stage compressor, what happens to the air after the first stage?

it is cooled in an intercooler Signup and view all the answers

What is the purpose of a tandem compressor arrangement?

to minimize dynamic loads Signup and view all the answers

What is the purpose of a cylinder water jacket in a compressor?

to cool the cylinder Signup and view all the answers

In a single-stage compressor, how many cylinders are typically used?

one or more Signup and view all the answers

What is the purpose of a crankshaft counterweight in a compressor?

to balance the load on the crankshaft Signup and view all the answers

In a double-acting compressor, what happens during the second stroke?

air is compressed and forced out of the cylinder Signup and view all the answers

What type of compressor is suitable for all ranges of pressure?

Reciprocating compressor Signup and view all the answers

Which type of compressor has only one compression stroke for each crankshaft revolution?

Single-acting compressor Signup and view all the answers

What happens during the inward stroke of a single-acting compressor?

More air is drawn into the cylinder Signup and view all the answers

What is the difference between a horizontal and a vertical single-acting compressor?

They are the same, only the orientation of the cylinder is different Signup and view all the answers

What happens in a double-acting compressor when the piston moves to the left?

A partial vacuum is formed in the right end of the cylinder and air is drawn in Signup and view all the answers

How many compression strokes are there for each revolution of the crankshaft in a double-acting compressor?

Two Signup and view all the answers

What type of compressor would best suit an industrial application requiring a high pressure ratio and large volume of compressed air?

Double-acting two-stage compressor Signup and view all the answers

Which compressor type would be least suited for an application requiring a constant, stable supply of compressed air?

Single-acting single-stage compressor Signup and view all the answers

In which type of compressor would it be most challenging to maintain equal pressure between the cylinder and the crankcase during operation?

Vertical double-acting compressor Signup and view all the answers

Which type of compressor would best suit a mining application requiring continuous operation with variable air pressure requirements?

Double-acting tandem compressor Signup and view all the answers

Which compressor type would be more susceptible to oil carryover issues resulting in contamination of the compressed air?

Double-acting tandem compressor Signup and view all the answers

Which type of compressor would be most efficient for an application requiring a low pressure ratio and constant, stable supply of compressed air?

Horizontal single-acting compressor Signup and view all the answers

What is the primary function of the crankcase door in a compressor?

To protect against leakage of oil and entrance of dust Signup and view all the answers

What is the purpose of the cylinder water jacket in a compressor?

To cool the cylinder and heads Signup and view all the answers

What is the primary advantage of using multiple cylinders in a compressor?

To increase capacity and smooth out discharge pressure Signup and view all the answers

What happens to the air after the first stage in a two-stage compressor?

It passes through an intercooler before entering the high-pressure cylinder Signup and view all the answers

What is the primary purpose of a tandem compressor arrangement?

To minimize dynamic loads by locating cylinders in pairs Signup and view all the answers

What is the function of the plate type valve in a compressor?

To control the flow of air into and out of the cylinder Signup and view all the answers

What happens in a double-acting compressor when the piston moves to the right?

Air is compressed and forced out through the right hand discharge valve Signup and view all the answers

What is the primary purpose of the oil screen in a compressor?

To filter out contaminants from the oil Signup and view all the answers

What is the primary purpose of intercooling in a two-stage compressor?

To reduce the temperature of compressed air Signup and view all the answers

What happens during the second stroke of a double-acting compressor?

Air is compressed and forced out through both discharge valves Signup and view all the answers

What material are the piston rings made of if oil-free operation is desired?

Graphite Signup and view all the answers

In a single-acting piston, what serves as the piston rod?

Connecting rod Signup and view all the answers

What is the material of construction for the compressor connecting rods?

Forged steel Signup and view all the answers

What does the crankshaft of a compressor often feature to balance reciprocating and rotating forces?

Counterweights Signup and view all the answers

What causes the automatic compressor valves to open and close?

Pressure difference Signup and view all the answers

In the plate disc type compressor valve design, what forces the valve to close?

Spring action Signup and view all the answers

Which part of the channel type compressor valve prevents metal-to-metal contact?

Valve channels Signup and view all the answers

What is the purpose of the air entering the port plate in the channel type compressor valve?

Closing the valve Signup and view all the answers

What is placed within the rectangular channels of the channel type compressor valve?

Valve springs Signup and view all the answers

What purpose do the stop plates serve in the channel type compressor valve?

Secure the valve springs Signup and view all the answers

What is the recommended cooling method for a compressor cylinder to maintain the manufacturers’ suggested operating temperature?

Water-cooling with a surrounding water chamber Signup and view all the answers

What type of material is typically used for compressor cylinders when operating at pressures above 6900 kPa?

Forged steel Signup and view all the answers

What is the construction material of choice for compressor pistons?

Steel or aluminum Signup and view all the answers

Which type of compressor piston is typically used in double-acting compressors?

Hollow pistons Signup and view all the answers

What prevents the piston rings from wearing out due to friction in a lubricated cylinder?

The piston rings are made of cast iron Signup and view all the answers

How does an air-cooled compressor cylinder cool itself?

By using integral cast fins Signup and view all the answers

What kind of material is typically used for compressor cylinders at pressures above 6900 kPa?

Forged steel Signup and view all the answers

Which cooling method is described as more efficient for compressor cylinders?

Water-cooling Signup and view all the answers

What type of pistons are commonly used in single-acting compressors?

Trunk type Signup and view all the answers

How are double-acting compressor pistons typically secured to the piston rod?

Taper fit against a machined shoulder with a locking nut Signup and view all the answers

What material are the piston rings made of in lubricated cylinders?

Cast iron Signup and view all the answers

Which type of cooling eliminates freezing hazards and has less piping requirements for compressors?

Air-cooling Signup and view all the answers

Which type of valve is depicted in Figure 15?

Plate disc type valve Signup and view all the answers

What material is used in the construction of the crosshead as described in the text?

Steel Signup and view all the answers

According to the description, how many crankpin bearings are present on the compressor connecting rods?

One Signup and view all the answers

What type of compressor valves are most commonly used, as mentioned in the text?

Automatic type Signup and view all the answers

Which figure in the description shows a crankshaft with counterweights?

Figure 13 Signup and view all the answers

According to the description, what is the purpose of the valve springs in the plate disc type compressor valve?

To force the valve closed Signup and view all the answers

What type of steel are the compressor crankshafts made from, as mentioned in the text?

Forged steel Signup and view all the answers

What purpose do the stop plates serve in the channel type compressor valve, as described in the text?

To hold the valve springs in place Signup and view all the answers

What material are the piston rings made of if oil-free operation is desired, as mentioned in the text?

Teflon Signup and view all the answers

What type of compressor would best suit a mining application requiring continuous operation with variable air pressure requirements, as mentioned in the text?

Rotary compressor Signup and view all the answers

What is the primary function of lubricating oil in a reciprocating compressor?

To provide a film between surfaces to prevent wear and reduce friction Signup and view all the answers

In external lubrication of a reciprocating compressor, oil is not supplied to which of the following parts?

Pistons Signup and view all the answers

How is lubricating oil delivered to the cylinder walls and pistons in a reciprocating compressor?

By a mechanical lubricator driven from the crankshaft or crosshead Signup and view all the answers

What type of lubrication system is typically used in small, single-acting, reciprocating compressors?

Splash lubrication system Signup and view all the answers

Where does the lubricating oil come from that is fed directly to the cylinder walls of a reciprocating compressor?

From an oil pump driven by the compressor shaft Signup and view all the answers

What function does internal lubrication of a reciprocating compressor provide?

To provide oil to the cylinder walls and pistons Signup and view all the answers

What is the primary function of the lubricating oil in the cylinder walls and pistons of a reciprocating compressor?

To provide a film between surfaces Signup and view all the answers

What type of lubrication system is used in small, single-acting, reciprocating compressors?

Splash lubrication system Signup and view all the answers

Where does the lubricating oil come from that is fed directly to the cylinder walls of a reciprocating compressor?

Pump driven by the compressor shaft Signup and view all the answers

What is the purpose of external lubrication in a reciprocating compressor?

To lubricate moving parts external to the compressor cylinder or casing Signup and view all the answers

What is the advantage of using a mechanical lubricator in a reciprocating compressor?

It feeds lubricating oil directly to the cylinder walls Signup and view all the answers

What is the primary function of lubricating oil in a reciprocating compressor?

To prevent wear by providing a film between surfaces Signup and view all the answers

What connects the shafts of the low-pressure and high-pressure casing in a rotary lobe compressor?

Timing gears Signup and view all the answers

What speeds can rotary lobe compressors operate at?

Up to about 1750 r/min Signup and view all the answers

What drives the concave rotor in a rotary screw compressor?

Timing gears Signup and view all the answers

What is the discharge pressure range for single-stage rotary screw compressors?

About 100 kPa Signup and view all the answers

What guarantees pulse-free delivery in a rotary screw compressor?

Having another lobe-flute space reach the outlet before the previous space empties Signup and view all the answers

Why is casing lubrication not required in rotary lobe compressors?

Because the rotor positions are maintained by timing gears Signup and view all the answers

What is the range of capacities for rotary screw compressors?

Up to 700 m3/min Signup and view all the answers

What guarantees smooth compression in a rotary screw compressor?

Two rotors trapping and compressing the air smoothly Signup and view all the answers

What drives the concave rotor in a rotary screw compressor?

Timing gears Signup and view all the answers

What is the primary advantage of using a rotary lobe compressor over a reciprocating compressor?

Compact size and even flow of air Signup and view all the answers

What is a common feature among all rotary compressors?

They provide energy to the fluid being compressed through the input shaft. Signup and view all the answers

What is the purpose of the water jacket surrounding the casing in a sliding vane compressor?

To cool the compressed gas. Signup and view all the answers

How do the sliding vanes move in a sliding vane compressor?

They move outward due to centrifugal force. Signup and view all the answers

What happens to the pockets of gas in a sliding vane compressor as the vanes move around the casing?

They decrease in volume. Signup and view all the answers

What is the maximum discharge pressure that a sliding vane compressor can operate at?

1000 kPa Signup and view all the answers

How many stages do sliding vane compressors often have?

Two Signup and view all the answers

What is the primary advantage of a rotary lobe compressor over a reciprocating compressor?

Compact design and even flow of oil-free air Signup and view all the answers

In a rotary screw compressor, what ensures pulse-free delivery of air?

Another lobe-flute space reaching the outlet before the previous space has completely emptied Signup and view all the answers

What is the range of discharge pressures for two-stage rotary screw compressors?

Up to 700 kPa Signup and view all the answers

What is the primary purpose of timing gears in a rotary lobe compressor?

To maintain rotor positions relative to each other Signup and view all the answers

What is the primary material used in the construction of a compressor cylinder operating at pressures above 1000 kPa?

Stainless steel Signup and view all the answers

What is the range of operating speeds for rotary screw compressors?

From 1500 to 12 000 r/min Signup and view all the answers

Why is internal lubrication not required in rotary lobe compressors?

Because the rotors do not touch each other or the casing Signup and view all the answers

What is the primary function of the water jacket surrounding the casing in a sliding vane compressor?

To provide additional cooling for the compressor Signup and view all the answers

What is the maximum discharge pressure range for single-stage rotary screw compressors operating at speeds up to 3000 r/min?

Up to 1000 kPa Signup and view all the answers

What is the primary advantage of using a rotary screw compressor over a reciprocating compressor?

Compact design and vibration-free operation Signup and view all the answers

What is the purpose of the convex rotor in a rotary screw compressor?

To drive the concave rotor Signup and view all the answers

Which type of compressor is suitable for all ranges of pressure, including high pressure applications above 6900 kPa?

Centrifugal compressor Signup and view all the answers

What is the primary advantage of using a rotary lobe compressor over a reciprocating compressor in terms of power requirements?

Lower power requirements Signup and view all the answers

What is the range of capacities for rotary lobe compressors?

Not mentioned in the text Signup and view all the answers

What is the function of an oil screen in a reciprocating compressor?

To prevent oil from entering the compression chamber Signup and view all the answers

What happens when the line pressure exceeds 793 kPa in the compressor system?

The blowdown valve opens the sump to the atmosphere. Signup and view all the answers

During compressor unloading, what prevents line pressure from returning to the sump?

Check valve in the air service line Signup and view all the answers

What initiates the return to full load (maximum) position in the compressor system once the air demand increases?

Supervisor energizing the solenoid valve Signup and view all the answers

What is the purpose of the spring in the actuator in the compressor system?

To return the spiral valve to the full load position Signup and view all the answers

What action allows the air pressure behind the Sullicon control to be vented in the compressor system?

Energizing the solenoid valve Signup and view all the answers

What is the consequence of the blowdown valve closing and the inlet butterfly valve opening in the compressor system?

Increase in sump pressure Signup and view all the answers

What is the purpose of the start pad in a compressor according to the text?

To reduce the starting current load for the motor Signup and view all the answers

In the Full Load Mode of the compressor operation, what is the purpose of the Supervisor?

To monitor the line air pressure Signup and view all the answers

During Modulation of the compressor operation, if the air demand drops below the rated capacity, what happens to the spiral valve?

It starts opening the bypass ports gradually Signup and view all the answers

What is the purpose of the differential pressure regulator controlling the Sullicon Control in the compressor?

To provide modulation range from 50% to 40% Signup and view all the answers

If the compressor is in Unload Mode, what indicates that the pressure is excess of 793 kPa?

The diaphragm chamber of the Sullicon Control expands Signup and view all the answers

During Full Load Mode, what maintains the spiral valve and the inlet butterfly valve in their respective positions?

Spring on the Sullicon control Signup and view all the answers

What happens to the inlet butterfly valve when the pressure exceeds 738 kPa during modulation?

It provides modulation range from 50% to 40% Signup and view all the answers

During Modulation, what is the function of the differential pressure regulator for the spiral valve?

Gradually open the bypass ports Signup and view all the answers

When the compressed air pressure in the sump rises above 345 kPa, what component opens to allow compressed air into the service line?

Minimum pressure valve Signup and view all the answers

If the rack engages with the pinion on the spiral valve shaft assembly, what is the likely outcome?

Spiral valve rotates Signup and view all the answers

What is the maximum output pressure of the rotary screw compressor?

793 kPa Signup and view all the answers

What is the purpose of the silicone-based fluid injected into the rotor cavity?

To lubricate, seal rotor clearances, and remove heat of compression Signup and view all the answers

What type of filter is used in the prefilters to remove particles down to 1 micron?

Coalescing oil filter Signup and view all the answers

What is the purpose of the afterfilter in the air dryer assembly?

To remove dust particles should the desiccant break down Signup and view all the answers

How is the air cooled in the fluid cooler/after cooler?

By using an electric powered fan and a radiator type cooler Signup and view all the answers

What is the purpose of the moisture separator?

To remove entrained moisture from the compressed air Signup and view all the answers

What is the function of the oil funnel in the water/oil separator?

To continuously skim off the oil from the surface Signup and view all the answers

What happens to the compressed air after the moisture separator?

It is directed to the prefilters Signup and view all the answers

What is the purpose of the fluid/air separator?

To remove entrained fluid from the air Signup and view all the answers

What is the capacity of the oil reservoir in the water/oil separator?

5 litres Signup and view all the answers

What is the purpose of the air inlet valve in the packaged industrial screw compressor?

To regulate the amount of air to the compressor unit according to service air demand Signup and view all the answers

What type of compressor is described as having two stages and being fluid lubricated?

Sullair Tandem Air Compressor Signup and view all the answers

What is the purpose of the spiral valve in the packaged industrial screw compressor?

To open and close by-pass ports in the stator Signup and view all the answers

What is the purpose of the air filter in the packaged industrial screw compressor?

To prevent dust and dirt from contaminating the compressor lubricating fluid Signup and view all the answers

What type of driver is commonly used in the packaged industrial screw compressor?

Electric motor Signup and view all the answers

What is the purpose of the moisture separator in the packaged industrial screw compressor?

To separate moisture from the air Signup and view all the answers

What happens to the spiral valve during modulation (690 kPa to 793 kPa)?

It opens the bypass ports gradually Signup and view all the answers

What is the purpose of the inlet butterfly valve during modulation?

To provide a modulation range from 100 to 50% Signup and view all the answers

At what point does the spiral valve move into the unload (minimum) position during modulation?

When the pressure exceeds 738 kPa Signup and view all the answers

Why is the differential pressure regulator controlling the Sullicon Control opened when the air pressure exceeds 738 kPa?

To partially close the inlet butterfly valve Signup and view all the answers

What happens when the spiral valve opens further during modulation?

All the bypass ports are fully open Signup and view all the answers

What is the purpose of the pinion mounted on the spiral valve shaft assembly?

To engage with the rack Signup and view all the answers

Why does the spiral valve provide a modulation range from 100 to 50% during the pressure range of 690 kPa to 793 kPa?

To optimize air compression based on demand Signup and view all the answers

What happens when the pressure rises above 793 kPa during modulation?

The differential pressure regulator controlling the Sullicon Control closes Signup and view all the answers

During modulation, what is the function of the rack that engages with the pinion?

To provide a rotary motion Signup and view all the answers

What function does the rack perform as it engages with the pinion mounted on the spiral valve shaft assembly during modulation?

Rotary motion Signup and view all the answers

What happens to the sump pressure when the blowdown valve opens the sump to the atmosphere?

It decreases to approximately 207 to 345 kPa Signup and view all the answers

What is the role of the check valve in the air service line?

To prevent line pressure from returning to the sump Signup and view all the answers

What happens when the line pressure drops back to 690 kPa?

The Supervisor energizes the solenoid valve Signup and view all the answers

What is the purpose of the vent hole at the spiral valve differential pressure regulator?

To decrease the air pressure Signup and view all the answers

What causes the spiral valve to return to the full load position?

A spring in the actuator Signup and view all the answers

What happens to the inlet valve and blowdown valve when the solenoid valve is de-energized?

The inlet valve closes and the blowdown valve opens Signup and view all the answers

What type of valve is used to regulate the amount of air to the compressor unit according to service air demand?

Butterfly valve Signup and view all the answers

What is the purpose of the air filter in the packaged industrial screw compressor?

To prevent dust and dirt from contaminating the compressor lubricating fluid Signup and view all the answers

What type of compressor is described as having a two stage, positive displacement, fluid lubricated type?

Rotary screw compressor Signup and view all the answers

What is the function of the bypass ports in the stator?

To return air to the suction before it can be compressed Signup and view all the answers

What drives the compressor in the packaged industrial screw compressor?

All of the above Signup and view all the answers

What is the purpose of the moisture separator in the packaged industrial screw compressor?

To separate fluids and air Signup and view all the answers

What is the primary function of the fluid/air separator in the rotary screw compressor?

To remove entrained fluid from the air Signup and view all the answers

What is the purpose of the coalescing oil filters in the prefilters?

To remove oil aerosols from the air Signup and view all the answers

What is the function of the electric powered fan in the fluid cooler/after cooler?

To move air across both sections of the cooler Signup and view all the answers

What is the purpose of the moisture separator in the compressor system?

To remove bulk moisture from the compressed air Signup and view all the answers

What is the function of the check valve in the air dryer assembly?

To direct the dried air via the outlet housing into the afterfilter Signup and view all the answers

What is the primary benefit of using a rotary screw compressor?

Pulse-free delivery of air Signup and view all the answers

What is the purpose of the adjustable oil funnel in the water/oil separator?

To continuously skim off the oil from the surface Signup and view all the answers

What is the function of the desiccant material in the air dryer assembly?

To dry the air through contact Signup and view all the answers

What is the primary purpose of the afterfilter in the air dryer assembly?

To remove dust particles Signup and view all the answers

What is the purpose of a centrifugal compressor?

Convert kinetic energy into pressure Signup and view all the answers

What surrounds the impeller in a centrifugal compressor?

Diffuser vanes Signup and view all the answers

In a centrifugal compressor, what happens as the gas moves radially outward from the center of the impeller?

Energy is transferred from the impeller to the gas Signup and view all the answers

What determines the portion of velocity energy in the gas that is converted to pressure within the impeller of a centrifugal compressor?

The degree of curvature of the impeller blades Signup and view all the answers

What role do diffuser vanes play in a centrifugal compressor?

Convert pressure into velocity Signup and view all the answers

Why is pressure converted in a centrifugal compressor more in the diffuser vanes than in the impeller?

Due to the decreasing velocity of the gas Signup and view all the answers

What is the primary advantage of a centrifugal compressor over a positive displacement type?

Oil-free air Signup and view all the answers

Which component of a centrifugal compressor allows for the adjustment of operating characteristics?

Diffuser vanes Signup and view all the answers

What is the primary purpose of the impeller eye vanes in a centrifugal compressor?

Shockless entry to the impeller Signup and view all the answers

What type of compressor has over-hanging impellers?

Single-stage compressor Signup and view all the answers

Which compressor component helps prevent metal-to-metal contact in the channel type compressor valve?

Stop plates Signup and view all the answers

What is the primary advantage of a rotary lobe compressor over a reciprocating compressor?

No need for casing lubrication Signup and view all the answers

What is the purpose of the shroud on a centrifugal compressor impeller?

To enclose the blades and prevent gas leakage Signup and view all the answers

Which component of a centrifugal compressor converts energy from velocity to pressure as the gas moves through?

The impeller Signup and view all the answers

What determines the portion of velocity energy in the gas that is converted to pressure within the impeller of a centrifugal compressor?

The degree of curvature of the impeller blades Signup and view all the answers

What is the primary role of the diffuser vanes in a centrifugal compressor?

To convert velocity energy to pressure Signup and view all the answers

What happens to the gas as it moves radially outward from the impeller of a centrifugal compressor?

It gains velocity and pressure Signup and view all the answers

Why do straighter impeller blades in a centrifugal compressor result in less pressure conversion in the impeller?

To minimize the energy losses Signup and view all the answers

What is the main advantage of a single-stage centrifugal compressor with a volute casing and a single impeller but no diffuser vanes?

Simple and rugged construction Signup and view all the answers

When a two-stage centrifugal compressor is in operation, what allows for a change in the operating characteristics of the compressor?

Adjustable diffuser vanes Signup and view all the answers

What is a disadvantage of centrifugal compressors compared to positive displacement types?

Poor performance in low-capacity work Signup and view all the answers

In a multi-stage centrifugal compressor shown in Figure 28 producing air at 1500 kPa, how is cooling achieved?

Water-cooling the diaphragms holding the diffusers Signup and view all the answers

What role do adjustable inlet vanes play in a compressor with diffuser vanes?

Regulate the amount of air reaching the impeller Signup and view all the answers

In a centrifugal compressor, how is the compression ratio affected if the compressor is installed at a high altitude?

Compression ratio decreases Signup and view all the answers

What direction does the gas travel in an axial flow compressor?

Axial direction Signup and view all the answers

What is the primary function of the moving blades in an axial flow compressor?

To increase the pressure of the air Signup and view all the answers

What happens to the pressure of the air as it passes through the fixed blades in an axial flow compressor?

It increases Signup and view all the answers

What is the purpose of having multiple stages in an axial flow compressor?

To obtain high discharge pressures Signup and view all the answers

What is the shape of the rotor assembly in an axial flow compressor?

Disc-like Signup and view all the answers

What is the shape of the outer casing of an axial flow compressor?

Constant diameter Signup and view all the answers

What is a characteristic of axial compressors?

They can supply large volumes at medium pressures. Signup and view all the answers

What is an advantage of axial compressors over centrifugal compressors?

They are more efficient. Signup and view all the answers

What is the primary application of axial compressors?

Supplying large volumes at medium pressures. Signup and view all the answers

What is a limitation of axial blades?

They are more subject to corrosion and erosion. Signup and view all the answers

What is a characteristic of the blades in an axial flow compressor?

They get gradually shorter toward the discharge end. Signup and view all the answers

What is the range of free air capacities for axial compressors?

2.8 m3 to 3700 m3/min. Signup and view all the answers

What type of pressure and volume are axial compressors suited to supply?

Medium pressure and high volume Signup and view all the answers

What is a disadvantage of axial blades compared to the impellers of centrifugal compressors?

Lower durability Signup and view all the answers

What is the efficiency comparison between axial compressors and centrifugal compressors?

Axial compressors are about 10% more efficient Signup and view all the answers

What are the operating speeds of axial compressors?

Up to 20,000 RPM Signup and view all the answers

What is a characteristic of the blades in an axial compressor as they extend towards the discharge end?

They get gradually shorter Signup and view all the answers

What is the range of free air capacities for axial compressors?

2.8 m3 to 3700 m3/min Signup and view all the answers

What is the primary factor that determines the number of stages required in an axial flow compressor to attain high discharge pressures?

The pressure rise per stage Signup and view all the answers

What is the main function of the fixed blades in an axial flow compressor?

To increase the pressure of the gas by converting velocity energy to pressure energy Signup and view all the answers

How is the energy transferred from the rotating shaft to the gas in an axial flow compressor?

By the rotation of the moving blades attached to the rotor Signup and view all the answers

What is the main advantage of axial flow compressors over centrifugal compressors?

Better aerodynamic efficiency Signup and view all the answers

What is the main purpose of the fixed blades in an axial flow compressor?

To increase the pressure of the gas by converting velocity energy to pressure energy Signup and view all the answers

What is the main factor that determines the number of stages required in an axial flow compressor to attain high discharge pressures?

The pressure rise per stage Signup and view all the answers

Study Notes

Compressor Terminology

A compressor receives a gas at a relatively low pressure and discharges it at a much higher pressure.
The compression ratio of a compressor is the ratio of the volume at the beginning of a compression stroke to the volume at the end.
Capacity is the quantity of air compressed and delivered in a given time period, expressed in terms of m3/min of free air.
Free air is air at atmospheric pressure, and capacity is the volume (in cubic meters) of atmospheric air compressed in one minute.
Staging involves compressing air in two or more stages to overcome low volumetric efficiency and high discharge temperature.
Each cylinder discharges into the next higher pressure cylinder, permitting a more moderate compression ratio in each cylinder.

Compressor Displacement

Compressor displacement is the volume swept out by the piston of a reciprocating compressor, expressed in cubic meters per minute.
If the compressor has more than one stage, the displacement is the volume swept out by the first stage piston only.

Intercoolers

Intercoolers are used to cool the compressed air between the stages of a multi-stage compressor.
Intercooling causes the compression to approach isothermal, reducing the power required for compression and increasing the overall capacity of the system.
Intercoolers may also cause moisture to condense out of the air, preventing free moisture from entering the next stage.

Aftercoolers

Aftercoolers are used to cool the compressed air before it is delivered to either the point of use or to the air receiver.
The temperature of the compressed air is reduced to significantly below the dewpoint at the discharge pressure, facilitating the removal of moisture and oil vapor from the compressed air stream.

Effects of Moisture

Free or atmospheric air always carries moisture as water vapor.
Saturated air, at normal temperature and atmospheric pressure, contains about 0.5 kg of moisture for every 28 m3 of air.
Moisture will be carried into the compressor with the air, and some of the moisture will drop out when the volume of the air is reduced by compression.
The water must be removed from the air because it has a detrimental effect on air-operated instruments and tools and may also freeze in the airlines.

Effects of Altitude

As the distance above sea level (i.e., altitude) increases, the atmospheric pressure decreases.
A compressor installed at a high altitude will require a higher compression ratio to produce the same discharge pressure as a machine at sea level.
A compressor will deliver less mass of air when operated in locations above sea level.

Single-Acting and Double-Acting Compressors

In a single-acting compressor, compression takes place at one end of the cylinder only.
In a double-acting compressor, compression occurs on both sides of the piston.
Double-acting compressors have a partial vacuum formed in one end of the cylinder and air is drawn in through the suction valve, while air is being compressed in the other end and forced out through the discharge valve.

Single-Stage and Two-Stage Compressors

A single-stage compressor may have one or more cylinders, and air is compressed in one cylinder to the final discharge pressure.
A two-stage compressor consists of two or more cylinders, with the first stage being larger in diameter than the second.
The air is first compressed in a low-pressure cylinder and then further compressed in a high-pressure cylinder to the final discharge pressure.

Tandem Compressors

Some dual-acting cylinders in high-pressure applications have a piston rod on both sides of the piston, to provide equal surface areas and to balance the load.
Tandem cylinder arrangements help minimize dynamic loads by locating cylinders in pairs, connected to a common crankshaft, so that the movements of the pistons oppose each other.### Reciprocating Compressor Components
Cylinders: made of cast iron for pressures up to 1000 kPa, cast steel for pressures up to 6900 kPa, and forged steel for higher pressures.
Cooling: necessary to remove heat generated by compression and friction; achieved through water-cooling or air-cooling.
Water-cooling: more efficient, but air-cooling has advantages of simple construction, less piping requirements, and no freezing hazard.

Pistons

Constructed of steel, cast iron, or aluminum.
Trunk type (automotive type) pistons used for single-acting compressors.
Double-acting compressor pistons may be solid or hollow.
Piston rings: made of cast iron for lubricated cylinders, Teflon or carbon for oil-free operation.

Crosshead

Made of steel with upper and lower bearing surfaces.
Piston rod fits into threaded hole in one end of the crosshead.
Crosshead pin attached to connecting rod, moves within bearings or bushings.

Connecting Rods

Constructed of forged steel.
Have crankpin bearing at one end and opening for crosshead pin at the other end.
Two designs: solid and hollow.

Crankshafts

Made of forged steel.
Drilled to provide oil passages for positive pressure lubrication.
Counterweights may be used to balance reciprocating and rotating forces.

Compressor Valves

Usually automatic, opening and closing due to pressure difference.
Two common designs: Plate Disc type and Channel type.
Plate Disc type: air enters through ribbed upper body, forcing circular valve discs downward against valve springs.
Channel type: air enters through port plate, pushing valve channels up off seat plate against valve springs.

Compressor Lubrication

Necessary to prevent wear, reduce friction, remove heat, reduce corrosion, and provide sealing.
External lubrication: lubricates moving parts external to the compressor cylinder or casing, including crankshaft bearings, connecting rod bearings, and crosshead.
Internal lubrication: provides lubricating oil to cylinder walls and pistons, using mechanical lubricator driven from crankshaft or crosshead.

Rotary Compressors

Features: provide energy to fluid through input shaft of rotating elements, no inlet or discharge valves, and classed as positive displacement.
Designs: sliding vane, rotary lobe, and rotary screw.

Rotary Lobe Compressor

Two rotors with figure-eight cross-section, revolving in opposite directions within a casing.
Timing gears used to maintain rotor positions.
Air trapped between lobes and casing wall, carried around to discharge on opposite side.
Advantages: compact, no inlet or discharge valves, oil-free air, and even flow.

Rotary Screw Compressor

Two intermeshing rotors, machined in the form of an axial screw, enclosed in a close-fitting casing.
Convex rotor driven, with four concave flutes.
Continuous compression, pulse-free delivery, and smooth flow.
Advantages: compactness, vibration-free operation, oil-free air, and no suction or discharge valves required.

Sliding Vane Compressor

Cylindrical rotor with flat, sliding vanes fitting into radial slots.
Rotor supported by bearings, eccentric to the casing.
Vanes forced outward against casing wall by centrifugal force, trapping gas pockets that decrease in volume as they move around the casing.
Advantages: high-speed operation, high discharge pressures, and compact design.### Rotary Compressors
Rotary compressors provide energy to the fluid being compressed through the input shaft of one or more rotating elements or rotors.
They do not have inlet or discharge valves.
Rotary compressors are classified as positive displacement compressors.

Rotary Lobe Compressor

Consists of two rotors with a figure-eight cross-section revolving in opposite directions within a casing.
Rotors always intermesh, preventing air from passing between them.
Timing gears maintain rotor positions relative to each other.
One rotor is driven directly, while the other is driven through timing gears.
Air is trapped between the lobe and the casing wall and carried around to the discharge on the opposite side of the casing.
Discharge pressures are relatively low (100 kPa for single-stage, 200 kPa for two-stage).
Advantages: compact, no inlet or discharge valves, and produces an even flow of oil-free air.

Rotary Screw Compressor

Consists of two intermeshing rotors, machined in the form of an axial screw, and enclosed in a close-fitting casing.
One rotor has four convex lobes, while the other rotor has six concave flutes.
Rotors do not come into contact with each other or with the casing, eliminating the need for internal lubrication.
The convex rotor is driven, which in turn drives the concave rotor through timing gears.
Air is smoothly compressed until it passes the discharge outlet.
Continuous compression takes place, ensuring pulse-free delivery.
Advantages: compact, vibration-free operation, smooth flow, oil-free air, and no suction or discharge valves required.

Sliding Vane Compressor

Consists of a cylindrical rotor with flat, sliding vanes that fit into radial slots.
Rotor is supported by bearings and is eccentric to the casing.
As the rotor turns, vanes are forced outward against the casing wall due to centrifugal force.
Pockets of air are trapped between the vanes and the wall and carried around the casing.
Due to the eccentricity, these pockets decrease in volume, compressing the gas as the vanes move around the casing.
Operate at speeds up to 3000 r/min with discharge pressures up to 1000 kPa.

Components of a Packaged Industrial Screw Compressor

Compressor driver
Air filter
Air inlet valve
Air compressor
Fluid/air separator
Fluid cooler/air after cooler
Moisture separator
Water/oil separator
Prefilters
Air dryer

Controls and Operation

Compressor driver: usually an electric motor, but can be a diesel engine or steam turbine.
Air filter: prevents dust and dirt from contaminating the compressor lubricating fluid.
Air inlet valve: regulates the amount of air to the compressor unit.
Spiral valve: used to open and close by-pass ports in the stator, varying the volume of compressed air produced.
Controls: include a Supervisor, which de-energizes the solenoid valve, bypassing the inlet valve differential pressure regulator.
Modes of operation: Start Mode, Full Load Mode, Modulation, and Unload Mode.

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Test your knowledge on compressor terminology including compression ratio and capacity. Learn about the definitions and calculations related to gas compression in this quiz.