Recent questions tagged compressed-air-system

Description : The coil of a transformer that is energized from a source of alternating voltage is known as the: A. low voltage winding B. high voltage winding C. primary winding D. secondary winding

Last Answer : C

Description : There is a single-phase motor connected in parallel with an electric heater unit. If the heater is switched off, then the overall power factor angle of the circuit will: A. increase B. decrease C. stay the same D. none of the above

Last Answer : A

Description : Explain about the air compressor modulation by optimal pressure settings. 

Last Answer : Very often in an industry, different types, capacities and makes of compressors are connected to a common distribution network. In such situations, proper selection of a right combination of compressors and ... different pressures and energy efficient ones must be made to meet most of the demand. 

Description : Explain the simple steps that can be followed in shop – floor for quantification of compressed air leakages.  

Last Answer : The following steps can be followed for quantification of compressed air leakages. Shut off compressed air operated equipments (or conduct test when no equipment is using compressed air). Run the compressor to ... per minute (cmm) T = Time on load in minutes T = Time unload in minutes 

Description : What are the methods of capacity control in centrifugal air compressors?  

Last Answer : Centrifugal compressors operate best at the design point. They are prone to surging at flow rates less than 50% of the rated capacity. The following types of controls are employed in ... variable speed drives to match compressor output to meet varying load requirements is by speed control 

Description : What is the effect of increase in altitude on the performance of single stage reciprocating compressors? 

Last Answer : With the increase in altitude, there will be reduction in air pressure, which results in increase in compression ratio, leading to higher discharge temperature and reduced efficiency. 

Description : Can you explain how temperature of inlet air affects the energy consumption of an air compressor?

Last Answer : As a thumb rule “for every 4 °C rise in inlet air temperature results in a higher energy consumption by 1% to achieve equivalent output”. Hence cool air intake leads to a more efficient compression.

Description : What are the most common types of compressed air dryers used? 

Last Answer : a. Heat – less dryer (absorption) b. Adsorption dryer c. Chiller dryer (refrigerated dryers)

Description : What are the different types of pressure regulators available for air compressor system? 

Last Answer : Pilot operated type Direct acting type Self – relieving type 

Description : List the advantages of keeping the discharge pressure for reciprocating compressors at minimum. 

Last Answer : Lower power consumption Less load on the piston rods and hence reduced maintenance costs Lower leakage losses

Description : List the means of capacity control for reciprocating compressors. 

Last Answer : On/off control Load and unload control Multi-step control

Description : What are the likely effects of using very cold water in intercoolers for reciprocating compressors? 

Last Answer : Use of very cold water can result in condensation which may result in water entering the cylinder, thereby reducing valve life, accelerating wear and scoring of piston, piston rings and ... and cause rust which will result in abrasion during compressor operation and significantly reduce efficiency. 

Description : Why inter-coolers are required for multi-stage reciprocating compressors?  

Last Answer : The intercoolers reduce the temperature of air/gas discharged between stages. Ideally, the intake temperature at each stage should be the same as that at the first stage (referred to a perfect cooling), so that the volume of air to be compressed does not increase and hence reduced power consumption.

Description : List the components of a compressed air system. 

Last Answer : The various components of a compressed air system are: • Intake air filters • Inter-stage coolers • After coolers • Air-dryers • Moisture traps • Receivers 

Description : Explain about the importance of optimal Pressure settings of a compressed air network 

Last Answer : The power consumed by a compressor depends on its operating pressure and rated capacity. They should not be operated above their optimum operating pressure as this not only wastes energy, but also leads ... switches must be adjusted such that the compressor cut-in and cuts-off at optimum levels. 

Description : What is the function of an air receiver?

Last Answer : The main purpose of a receiver is to act as a pulsation damper, allowing intermittent high demands for compressed air to be met from a small compressor set, resulting in lesser energy consumption. 

Description : What is a surge point and how do you prevent surging, in centrifugal compressors?

Last Answer : Surge point is the point on the performance curve where a further decrease inflow (typically in the region of 50-70 % of rated capacity) causes instability, resulting in a pulsating flow, ... to thrust reversals, or excessive vibration. Bypass valves advents are commonly used to prevent surging. 

Description : What are the limitations of a centrifugal compressor operation? 

Last Answer : The major limitation of a centrifugal compressor is that is operates at peak efficiency at design point only and any deviation from the operating point is detrimental to its performance. When selecting ... at high pressure, with the consequent reduction in flow, the surge point is not reached.

Description : Briefly describe about ‘rotary compressor’?  

Last Answer : Rotary compressors have rotors in place of pistons and give a continuous, pulsation free discharge. They operate at high speed and generally provide higher throughput than reciprocating compressors. They are directly ... , vibrate less, and have a lower number of parts which are subject to wear. 

Description : Give major classifications of compressors and the basic principle of its working.  

Last Answer : The major classifications of compressors are positive displacement and dynamic type. Positive displacement can be further divided in to (a) Reciprocating (b) Rotary. Dynamic compressors divided into Radial and ... increase the air or gas velocity, which is then converted to increase the pressure. 

Description : If the compressor of 200 cfm loads in 10 seconds and unloads in 20 seconds, the air leakage would be_____ a) 67 cfm b) 100 cfm c) 10 cfm d) 133 cfm 

Last Answer : a) 67 cfm

Description : Which of the following parameters are not required for evaluating volumetric efficiency of the compressor? a) Power b) Cylinder bore diameter c) Stroke length d) FAD

Last Answer : a) Power

Description : From base load operation and from achieving best specific energy consumption point of view, which of the following compressors are suitable? a) Single stage reciprocating compressors b) Centrifugal compressors c) Two stage reciprocating compressor d) Multi stage reciprocating compressor

Last Answer : b) Centrifugal compressors

Description : From the point of lower specific energy consumption, which of the following compressors are suitable for part load operation? a) Two stage reciprocating compressors b) Centrifugal compressors c) Two stage screw compressor d) Single stage screw compressor

Last Answer : a) Two stage reciprocating compressors

Description : The likely estimate on equivalent power wastage for a leakage from 7 bar compressed air system through 1.6 mm orifice size is ____ a) 0.2 kW b) 3.0 kW c) 0.8 kW d) 12 kW

Last Answer : c) 0.8 kW

Description : The acceptable pressure drop at the farthest point in mains header of an industrial compressed air network is: a)0.3 bar b) 0.5 bar c) 1.0 bar d) 2 bar

Last Answer : a)0.3 bar

Description : Reduction in the delivery pressure of a Compressor working at 7 bar, by 1 bar would reduce the power consumption by a) 6 to 10 % b) 2 to 3 % c) 12 to 14 % d) None of the above

Last Answer : a) 6 to 10 %

Description : Identify the correct statement for air compressors. a. For every 5.5oC drop in the inlet air temperature, the increase in energy consumption is by 2%. b. For every 4 oC rise in ... increase in energy consumption is by 1% d. The energy consumption remains same irrespective of inlet air temperature 

Last Answer : c. For every 4 oC rise in the inter air temperature, the increase in energy consumption is by 1% 

Description : Which of the statement is True for centrifugal compressors? a) The compressor should not be operated at full load b) The compressor should be operated at shut off pressure c) The ... operated with inlet-guide vane control d) The compressor should not be operated close to the surge point 

Last Answer : d) The compressor should not be operated close to the surge point

Description : The percentage increase in power consumption of a compressor with suction side air filter and with the pressure drop across the filter of 200 mmWc is ____ a) 1.0% b) 3% c) 2.4% d) 1.6% 

Last Answer : d) 1.6%

Description : For every 4°C raise in air inlet temperature of an air compressor, the power consumption will increases by_____ a) 2% b) 1% c) 3% d) 4%

Last Answer : b) 1%

Description : The basic function of air dryer in a compressor is: a. prevent dust from entering compressor b. storage and smoothening pulsating air output c. reduce the temperature of the air before it enters the next state to increase efficiency d. to remove remaining traces of moisture after after-cooler 

Last Answer : d. to remove remaining traces of moisture after after-cooler 

Description : The ratio of isothermal power to actual measured input power of a compressor is known as: a) Isothermal efficiency b) Volumetric Efficiency c) Barometric efficiency d) None 

Last Answer : a) Isothermal efficiency

Description : The volumetric efficiency of the compressor ______ with the increase in altitude of place a) increases b) decreases c) does not change d) None

Last Answer : b) decreases

Description : The compression ratios for axial flow compressors are ____. a) Lesser b) Higher c) moderate d) None 

Last Answer : b) Higher

Description : The discharge temperature of two stage compressor compared to single stage one is ____ a) Lesser b) Same c) Higher d) None  

Last Answer : a) Lesser

Description : The specific power consumption of non lubricated compressor compared to lubricated type is ____ a) Lesser b) Same c) Higher d) None 

Last Answer : c) Higher

Description : Vertical type reciprocating compressors are used in the capacity range of _____ a) 50 – 150 cfm b) 200 – 500 cfm c) Above 10ooo cfm d) 10 – 50 cfm 

Last Answer : a) 50 – 150 cfm

Description : The compressor capacity of a reciprocating compressor is directly proportional to __ a) Speed b) Pressure c) Volume d) All 

Last Answer : a) Speed

Description : Which of the following type does Screw compressor belongs to? a) Positive displacementcompressor b) Dynamic compressors c) Both a & b d) None of the above 

Last Answer : a) Positive displacementcompressor