IN Engineering

About compressor controls Since compressed air is generally required in varying quantities at the relatively constant pressure, compressor regulators or controls are used to vary the  delivery of the compressor. if the pressure rise too high , The pilot (pressure responsive device) operate to reduce the air delivery. If pressure falls too Low, The pilot operated to increase the delivery of air. Several mechanisms are used as unloading devices to very the delivery of compressed air. (1) the inlet valves may be held open during both the suction and compression stroke -  thus no air  will be compressed in the cylinder. (2) clearance pockets may be used which are automatically controlled by the pilot ,reducing the volume of compressed air delivery. (3) on rotary compressor, a valve which completely closed  the intake line, prevent the intake of air. (4) on some compressors the speed is varied in response to pressure changes on the pilot.  as the  volume of outp...

Air or gas compression causes temperature increase which become high enough to cause trouble with the lubrication of the cylinder piston and packings. Cooling  of the air and of the compressor cylinder reduce this problem and also the required work of compressions,approaching  the minimum of an isothermal process. WHAT IS ISOTHERMAL PROCESS an isothermal process is, thermodynamic   process  in which the temperature of a system remains constant. The transfer of heat into or out of the system happens so slowly that thermal equilibrium is maintained. At a particular constant temperature, the change of a substance, object or system is known as Isothermal Process.  In general, during an isothermal process there is a change in internal  energy ,  heat energy , and  work , even though the temperature remains the same. Something in the system works to maintain that equal temperature. This may be done by circulating atmospheric air or water over the cylind...

Non Lubricated Compressors where high pressure purity is required, as instrumentation air systems,non lubricated compressor should be used or consider. The reciprocating compressor is available as a non lubricated model with carbon or Teflon rings. new filtering problems may arise due to the type of oilless design used, such as carbon dust from worn carbon rings in the compressor. also, multistaging may be required to attend a desired pressure due to temperature limitation. Rotary liquid piston and centrifugal compressors eliminate the need for lubricating oil or oilless design since no internal lubrication is required on either type. initial cost of the liquid piston compressor is higher but is offset by reduced maintenance cost.  With water as a ceiling medium no after cooler is needed to remove the heat of compression or foreign matter which may be present in the incoming air. This non lubricated Teflon ring allows reciprocating compressor to be operated without lubrication that...

Axial flow compressor axial flow compressor is a must see with aerodynamically shaped,radial  blades in both rotor and casing air passes into the machine through The first row of rotor blades and is then redirected into the next and successive Rows by alternates rows of fixed diffusing blades in the casing. flow rating as high as 1,000,000  cubic feet per minute for pressure similar to those of centrifugal machines are available. Axial flow machines are characterized by ess entially constant volume delivery at variable pressure, whereas centrifugal machines deliver practically constant pressure over a variable capacity range . these machines are rarely used for instrument air systems.

 Centrifugal compressor In a multistage centrifugal compressor with intercooler, air  enters the first stage compressor casing  and passes into the eye or centre of the first stage impeller. The rotation of the impeller imparts a high velocity to the air as it moves  radially outward into the diffuser or intercooler area where its temperature is reduced. The air  is then directed into the eye of the second stage impeller where more compressions takes place and similarly to each stage of the machine.  multistage-centrifugal air compressors are generally used for handling large air volumes at pressures up to 150 PSI and higher . centrifugal compressors are often used for  instrument air services.multistage units can handle large air volumes at pressure to 150 psig and higher.

 Dynamic compressors Dynamic compressor are machines in which air or gas is compressed by the dynamic action of rotating blades or vanes which accelerate and compressed gas .  Some pressure increase result directly as the gas velocity is increased due to its acceleration by the blades.as the gas pass into the diffuser section of the compressor, the large part of velocity head is recovered as the pressure increase accompanied by a corresponding velocity decrease. centrifugal and axial flow compressor are included in this classification. dynamic compressors are characterized by large volumetric capacity and relatively low pressure, although higher pressure are produced by multistage machines.  Both centrifugal and axial compressors inherently high speed machines.

 Liquid piston cylinder compressor  The compressing medium in this unit is a liquid usually water.  the plates of the rotor form a series of buckets carrying the liquid around elliptical casing. The liquid following the control of the inside of the casing surges back into the pockets at the narrow section the air in the pockets is compressed and discharge to properly located ports. With continuous rotation the ring of liquid surges out of the bucket in two broad section of the casing and a new load of air is drawn in through the inlet ports and the cycle begin again. Two compression cycles are completed per revolution. these units are available in 50 to 100 psig pressure ranges  at flow 20 to 450 standard cubic feet per minute .

 Screw compressor In screw compressors two helical rotors turn freely with a controlled clearance between the rotors and the housing oil is injected into the compression chamber to provide lubrication and compression seal. This crew compressor is available at pressure 200 PSIg in flow ranges from 400 to 100  scfm . Most of this oil is removed in some type of air receive or oil separator for use in the compression process. At pressure of 100 PSIg  the flow  range is 400 to 1300 standard cubic feet per minute .

Sliding vane type rotary compressor   In a sliding vane compressor ,an eccentrically mounted cylindrical slotted rotor turn within a large diameter housing as shown in the figure. Rectangular vanes  slide in and out of the rotor slots and are held against the casing wall by centrifugal force as the rotor turns, air is compressed between the vanes and discharge through a port on the compression side.  Oil is injected into the compression chamber to provide lubrication and a compression seal. most of this oil is remove in an oil/air separator for reuse in the compression process. This type compressor produce pressure up to 125 psig in one or two stage at flows of 100 to 600 standard cubic feet per minute. This is not likely to be used is specially for instrument air but might be used in a system from which in instrument air is taken.

 Reciprocating compressor Reciprocating compressor is a type of positive displacement compressor.We know that   positive displacement compressor are machine in which successive volume of air or gas are confined within a closed space. A reduction in a volume of this   space  result in an increase in the gas pressure. The  reciprocating compressors are probably the most common of all the types of compressor. it comes in many sizes and configuration such as a single or double acting ,single or multi cylinder with  cylinders arrange in a number of different ways. The trunk type reciprocating air compressor operate similarly to the two cycle engine with the exception that the crank shaft is driven from an external source. No fuel is injected into the cylinder and the compressed gas is discharge at the peak of the compression stroke into a storage receptacle. How to two  cycle engine work A  two-stroke  (or  two-cycle )  engine ...