[Mechanical Equipment Technology Edition] Daily Question 201803028: Gas flow regulation mechanism of screw refrigeration compressors (2)
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This post was last edited by YORK Industrial Refrigeration on 2018-3-30 08:32. This year’s 【Daily Question】 is divided into three categories: screw refrigeration compressors, refrigeration systems, and oil circuit systems, aiming to provide a comprehensive understanding of refrigeration technology. (If you encounter something you don’t know or can’t answer, please actively look up information; by doing so, your skills will improve!) ) All participants in the comments on this post will receive 1-3 wealth points; those who give complete answers will get 10-15 points, with the validity period being two days. ============================== Screw refrigeration compressor airflow control mechanism (2): What is the role of energy regulation in refrigeration equipment? What is the principle of regulation by a slide valve? (Note: Refer to Figure B below regarding the return air flow and the chamfer on the slide valve; this will be addressed in a subsequent question.) Answer: 1. To match the cooling capacity of the machine to the heat load of the warehouse, enabling startup under no-load or light-load conditions and thereby reducing the impact on the surrounding power grid. 2. By moving the slide valve, the working volume between the male and female screw teeth of the compressor remains connected to the suction port for a period of time as the contact line between the tooth surfaces moves from the suction side toward the discharge side, allowing this gas to flow back to the suction port. Energy regulation is achieved by reducing the effective working length of the screw. ============================== High-quality promotions: Mechanical equipment——Videos on the repair and adjustment of York compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment——Maintenance procedures for York screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment——Upgrading of York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment——Major repairs of GEA Grasso screw compressors https://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment——Disassembly and maintenance of British HOWDEN screw compressors https://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment——Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
Screw refrigeration compressors commonly use slide valves to regulate energy; that is, a slide valve that can move axially is installed on the high-pressure side of the two rotors in order to control energy flow and enable unloaded starting. The principle of energy regulation using a slide valve involves the axial movement of the slide valve along the screw, thereby changing the effective axial working length of the screw and allowing for continuous, stepless adjustment of energy between 100% and 10%.
First, it ensures that the cooling capacity of the refrigeration unit always matches the external heat load, thereby improving the economic efficiency of the system’s operation； Second, reduce the range of fluctuations in the evaporation pressure (or evaporation temperature) to improve the control accuracy of the refrigeration unit, and prevent frequent starting and stopping of the compressor ； Third, it ensures that the refrigeration compressor starts under light load, preventing excessive fluctuations in the electrical grid load, improving the efficiency of the motor, and extending the service life of the compressor. The principle of energy regulation using a slide valve is to utilize the axial movement of the slide valve along the screw to change the effective axial working length of the screw, thereby enabling continuous, stepless adjustment of the gas flow rate within the range of 10% to 100%.
The main function of energy regulation in refrigeration equipment: First, it ensures that the cooling capacity of the refrigeration unit remains matched to the external heat load, thereby improving the economic efficiency of the system’s operation； Second, reduce the range of fluctuations in the evaporation pressure (or evaporation temperature) to improve the temperature control accuracy of the refrigeration and air conditioning system, and prevent frequent start-up and shutdown of the compressor ； Third, ensure that the refrigeration compressor starts under light load, thereby avoiding excessive fluctuations in the power grid load and improving the efficiency of the motor’s operation. The principle of energy regulation using a slide valve involves the axial movement of the slide valve along the screw, thereby changing the effective axial working length of the screw and allowing for continuous, stepless adjustment of energy between 100% and 10%.
Screw refrigeration compressors commonly use slide valves to regulate energy. The principle of energy regulation using a slide valve involves the axial movement of the slide valve along the screw, thereby changing the effective axial working length of the screw and allowing for continuous, stepless adjustment of energy between 100% and 10%
What is the purpose of energy regulation in refrigeration equipment? First, it ensures that the cooling capacity of the refrigeration unit always matches the external heat load, thereby improving the economic efficiency of the system’s operation ； Second, reduce the range of fluctuations in the evaporation pressure (or evaporation temperature) to improve the temperature control accuracy of the refrigeration and air conditioning system, and prevent frequent start-up and shutdown of the compressor ； Third, ensure that the refrigeration compressor starts under light load, thereby avoiding excessive fluctuations in the power grid load and improving the efficiency of the motor’s operation. What is the principle of regulation by a slide valve? At the intersection of the two inner circles on the high-pressure side of the screw refrigeration compressor’s casing, an adjustable slide valve equipped with radial exhaust ports and a corresponding fixed block are installed, forming part of the compressor casing. The slide valve can move back and forth in a direction parallel to the cylinder axis; the most common method of driving it is hydraulic drive, with the required oil pressure provided by the compressor’s own oil circuit system. The fixed block can be movable in order to allow adjustment of the volumetric ratio of the compressor at full load, or it can be fixed; in this case, different slide valves with various positions for the radial exhaust ports are used to change the volumetric ratio at full load, thereby enabling the compressor to operate under different operating conditions.
The main functions of energy regulation are: first, to ensure that the cooling capacity of the refrigeration unit always matches the external heat load, thereby improving the economic efficiency of the system’s operation； Second, reduce the range of fluctuations in the evaporation pressure (or evaporation temperature) to improve the temperature control accuracy of the cooled object, and avoid frequent start-up and shutdown of the compressor ； Third, ensure that the refrigeration compressor starts under light load, thereby avoiding excessive fluctuations in the power grid load and improving the efficiency of the motor’s operation.
Sliding valve regulation principle: That is, by changing the effective working length of the rotor, gas flow rate can be adjusted
The role of energy regulation； It is to meet the requirements of the operating conditions. Principle of slide valve regulation ； At the intersection of the two inner circles on the high-pressure side of the screw refrigeration compressor’s casing, there is a regulating slide valve equipped with radial exhaust ports, along with a corresponding fixed block; these form part of the compressor’s casing. The slide valve can move back and forth in a direction parallel to the cylinder axis. The most common method of driving it is hydraulic drive, with the required oil pressure provided by the compressor’s own oil circuit system. The fixed block can be movable, allowing the volume ratio of the compressor at full load to be adjusted; it can also be fixed, and in that case, different slide valves with varying radial exhaust port positions are used to change the volume ratio at full load, thereby enabling the compressor to operate under different conditions.
The slide valve regulates the cooling capacity of the compressor, taking into account the operating characteristics of screw compressors. When the low-pressure end face of the slide valve is in contact with the fixed block, the compressor is operating at full load. After the suction process ends, a sealed volume is formed within the working chamber. As the rotor rotates, the volume of this working chamber decreases, and the gas pressure rises gradually along the axis. Geographically, the working chamber moves from the suction end toward the discharge end of the compressor. If there is a bypass passage between the low-pressure end face of the slide valve and the fixed block, the effective working length of the rotor decreases, and the compressor operates at partial load. When the working chamber attempts to increase the gas pressure after the suction process ends, it connects to the bypass passage, allowing some of the gas to flow back to the low-pressure chamber at suction pressure, thus enabling regulation of the compressor’s cooling capacity. Once the rotor’s contact line passes over the bypass passage, the working chamber becomes completely sealed, and normal compression processes resume.
In screw refrigeration compressors, the volume ratio corresponding to the axial exhaust ports, whose positions are fixed, is greater than that corresponding to the radial exhaust ports. When the slide valve moves in the direction of unloading, a bypass passage is created between the slide valve and the fixed block; the radial exhaust ports also move backward, delaying the moment when the working chamber connects to the exhaust ports. This continues until the radial exhaust ports become as large as the axial ports, thereby achieving both regulation of the cooling capacity and the volume ratio, and addressing any mismatch in internal and external pressure ratios caused by cooling capacity adjustments.
The slide valve regulates the cooling capacity of the compressor, taking into account the operating characteristics of screw compressors. When the low-pressure end face of the slide valve is in contact with the fixed block, the compressor is operating at full load. After the suction process ends, a sealed volume is formed within the working chamber. As the rotor rotates, the volume of this working chamber decreases, and the gas pressure rises gradually along the axis. Geographically, the working chamber moves from the suction end toward the discharge end of the compressor. If there is a bypass passage between the low-pressure end face of the slide valve and the fixed block, the effective working length of the rotor decreases, and the compressor operates at partial load. When the working chamber attempts to increase the gas pressure after the suction process ends, it connects to the bypass passage, allowing some of the gas to flow back to the low-pressure chamber at suction pressure, thus enabling regulation of the compressor’s cooling capacity. Once the rotor’s contact line passes over the bypass passage, the working chamber becomes completely sealed, and normal compression processes resume.
In screw refrigeration compressors, the volume ratio corresponding to the axial exhaust ports, whose positions are fixed, is greater than that corresponding to the radial exhaust ports. When the slide valve moves in the direction of unloading, a bypass passage is created between the slide valve and the fixed block; the radial exhaust ports also move backward, delaying the moment when the working chamber connects to the exhaust ports. This continues until the radial exhaust ports become as large as the axial ports, thereby achieving both regulation of the cooling capacity and the volume ratio, and addressing any mismatch in internal and external pressure ratios caused by cooling capacity adjustments.