This thickness is measured with vernier caliper or micrometer and is then compared with the manufacturer’s value. Reciprocating compressors of various designs and applications are encountered nowadays throughout refining, petrochemical and process industries as well as in power generation and environmental engineering. 3 Figure 4 shows the pressure – volume diagram for an ideal reciprocating compressor. If too much clearance is present, no gas will be discharged. Traditional capacity control methods waste electric power by using recycle valves or recycle valves in combination with step control. Only when the pressure of this gas reaches to certain minimum level, the suction valve opens. By doing this the lead ball will compress and the thickness obtained is the clearance volume. The operation of reciprocating compressors may seem simple. Cross Section of Typical Reciprocating Compressor Figure 2. Large bumping clearance retards the formation of vacuum on the suction stroke and thus less air is drawn inside for compression and accordingly the weight of the air delivered is reduced proportional to the clearance volume. Cross Section of Typical Reciprocating Compressor V. OPERATING RANGE OF RECIPROCATING COMPRESSOR Unwanted effects of these waves are oscillating moments on the piston, increased valve losses and decreased compressor efficiency. Inserting shims will move the connecting rod and the piston which will change the clearance. Clearance volume in actual reciprocating compressors is essential a) To accommodate Valves in the cylinder head b) To provide cushioning effect c) To attain high volumetric efficiency d) To provide cushioning effect and also to avoid mechanical bang of piston with cylinder head Small clearance volume may result in piston banging or colliding to the cylinder head. 2 Effect of Clearance 11 Factors Affecting R Compressor Performance From Fig. During compression, the pressure distribution in the cylinder is almost uniform, but when the pressure valve opens, a rarefaction wave is initiated, which travels back and forth in the compression chamber. This E-Tip will look at the compression cycle for a reciprocating compressor. The performance aspects of ideal reciprocating compressors with clearance, specifically: a) Effect of evaporator temperature on system performance at a fixed The compression ratio, R, of the reciprocating compressor is defined as the ratio of the suction pressure of the refrigerant to the discharge pressure of the refrigerant. Reciprocating Compressor Effect of the clearance . This is the series of articles that describes the difference between the refrigeration compressors and air compressors, types of refrigeration compressors, principle of working of the reciprocating compressors and parts of the reciprocating compressors. SOLUTION Swept Volume = V Clearance volume = 0.05 V ... Effect of altitude; Brake horsepower; CHARACTERISTICS OF RECIPROCATING COMPRESSORS. Bumping Clearance or Clearance volume. These are compression ratio, capacity and volumetric efficiency of the compressor. Effects Due to Less Clearance. The illustrated volumes of 5%, 10% and 15% usually satisfy a reasonable process compressor range. - n is the number of cylinders in the compressor, - N is the speed of the rotation of the crankshaft that can be expressed in rotations per minute (rpm) or rotations per second (rps). V = Actual volume of gas sucked by the compressor/ Theoretical volume of the compressor. The expansion part of the cycle follows the law pV 1.2 = C. The crank speed is 360 rev/min. The extra clearance would result in a small volume of air being re-expanded every time causing increase in air temperature, fall in efficiency and overheating of the compressors. The effect of clearance volume is shown in Figures 18-17A and 18-17B [100]. clearance volume of a compressor actually should be minimum enought 2 avoid piston from striking the head(thermal expansion and valve clearance should be given)..it should be minimum bcos greater the clearance more compressed gas tht left in the cylinder after each compression stroke, so tht leads to energy loss and lower efficiency..(volumetric In figure 2 an application with a 2.7:1 compression ratio is shown with clearance volumes … Cylinder, Piston, Connecting Rod, Crankshaft: Parts of Reciprocating Compressor, Batch vs. Excessive clearance in a compressor cylinder can cause slamming of the discharge valves. Lesser the volumetric efficiency less is the capacity of the compressor. The clearance volume limits the compression ratio and thus the maximum pressure.developed, When the compressor first starts in an empty system, it discharges virtually all the swept volume of air that the piston displaces, and as pressure builds up, the compressor will discharge only the compressed air that is greater than is in the system, delivering less with each stroke, until the pressure in the cylinder equals … However, complex phenomena are associated with these machines. The mechanical efficiency of the compressor is 85%. Clearance volume in compressors varies from 1.5% to 35% depending upon type of compressor. In applications where the compression ratio is relatively small, the extra clearance volume has a lesser effect on the volumetric efficiency. Large reciprocating compressors are a poor match for variable-speed drives because the large motors make the drives costly and the high torque requirements require large flywheels. The capacity of the compressor is very important parameter, since the capacity of whole refrigeration or the air conditioning plant depends on it. Analysis of Cycle Compressor with clearance volume . In addition to explaining the compression process, it will introduce the concept of unswept clearance volume in the cylinder, which will be important in the next E-Tip in this series, where we will evaluate compressor capacity. below the atmospheric pressure. A controllable variable volume clearance pocket for reciprocating compressor cylinders is disclosed. - L is the stroke of the piston inside the cylinder, which can also be the length of the bore. In a reciprocating compressor, the capacity depends on the volume displaced by the piston during its movement. The specific objectives of this lecture are to: 1. The volumetric efficiency of the compressor also affects the capacity of the compressor since the capacity is directly dependent on the piston displacement inside the cylinder. **Learn To Do Troubleshooting And Maintenance Of Marine Electrical Systems**        Click Here To Know How, By Hiteshk | In: Air Compressor | Last Updated on October 7, 2019. Fig.4 The piston reciprocates drawing in gas, compressing it … Bumping clearance can be adjusted with the help of inserting shims (thin metallic plates) in the bottom bearings. 2. 3 or Previous Eqations it can be seen that Volumetric Efficiency, and hence Capacity, Decreases as … The volume flow rate per unit capacity, V is given by: e e e SW. V,cl q v Q.V V = η = (19.6) As evaporator temperature increases the specific volume of the refrigerant at compressor inlet reduces rapidly and the refrigerant effect increases marginally. The manual specifies the limit for this and it will depend on the manufacturer. Thus as the compression ratio of the compressor increases, its volumetric efficiency and the capacity reduces. Fig. a Gas is compressed in a reciprocating compressor from 1 bar to 6 bar. Required fields are marked *. Compression Ratio of the Reciprocating Compressor The volumetric efficiency (V) of the compressor is defined as the ratio of the actual volume of gas sucked by it to the theoretical volume that it could have sucked if clearance volume was not present. The work done for compression of air polytropically can be given by the are a enclosed in cycle 1-2- 3-4. In the control and operation of a reciprocating gas compressor, the goal is efficiency: compressing the greatest volume of gas for the least cost. The third term is defined as a secondary volumetric efficiency, which takes into account all other irreversible phenomena that occur inside the compression chamber. As written above, fr adjusting the bumping clearance put a shims to the bottom bearing. 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