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The main components of turbo-prop engine are a propeller, gear reduction unit, a compressor, a combustor, gas turbine and the nozzles. In this engine 80 to 90% of the total propulsive thrust is generated by the gas turbine and the remainder is developed by the expansion of the gases in nozzles. Due to this the power generated in the gas turbine is used for driving the compressor and the propeller, while in case of turbojet engines the turbine power is only used to drive the compressor and the auxiliaries.

1. On the basis of combustion process a) Constant pressure type b) Constant volume or explosion type 2. On the basis of path of working substance a) Open cycle gas turbine b) Closed cycle gas turbine 3. On the basis of action of expanding gases a) Impulse gas turbine b) Impulse reaction gas turbine 4. On the basis of direction of flow a) Axial flow b) Radial flow

Operating or moving or allowing movement in one direction only. It runs in one direction only. It does not run in the other direction. Unidirectional motor can be operated by using 3/2 DC valve as shown in fig. Bidirectional air motor: Functioning or allowing movement in two usually opposite directions. It can runs in both direction. Bi-directional motor can be operated by using 4/3 DC valve as shown in fig

1. Relatively low accuracy: As pneumatic systems are powered by the force provided by compressed air, their operation is subject to the volume of the compressed air. As the volume of air may change when compressed or heated, the supply of air to the system may not be accurate, causing a decrease in the overall accuracy of the system. 2. Low loading: As the cylinders of pneumatic components are not very large, a pneumatic system cannot drive loads that are too heavy. 3. Processing required before use Compressed air must be processed before use to ensure the absence of water vapour or dust.

FRL unit means Filter Regulator and Lubricator Unit Function of FRL unit Filter (F) – 1) To remove the micron and sub-micron particles present in the entering air of compressor 2) Used to separate out contaminants like dust, dirt particles from the compressed air Regulator (R)–In pneumatic system the pressure of compressed air may not stable due to possibility of line fluctuation. Hence there is a need to maintain and regulate the air pressure. This function is performed by regulator. Lubricator (L) – Sliding components like spool, a pneumatic cylinder has sliding motion between parts.

Double acting reciprocating air compressor is similar to double acting reciprocating pump. It is comprised of following parts: 1) Cylinder 2) Piston and piston rod and connecting rod. 3) Crank and crank case 4) Two suction valves and two delivery valves. 5) One inlet port and one outlet port It uses four bar mechanism. There are 4 valves (2 suction valves and 2 delivery valves) shown at A, B, C, D in figure. There are cooling fans similar to single acting compressors. The crank rotates on electric motor/engine/turbine.