【Mechanical Equipment Technology Edition】Daily Question 20171227: Common Faults in Refrigeration Systems (4)
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This post was last edited by YORK Industrial Refrigeration on 2017-12-29 at 08:34. Starting from now, in order to enhance communication among users, a 【Daily Question】 activity has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 wealth points for active participation, 10-15 wealth points for correct answers. This question is valid for two days; no score will be assigned after that period. In a refrigeration compressor, how does the slide valve control of the compressor’s energy regulation device achieve self-regulation? In general, in chillers, control is achieved through the outlet water temperature; in freezers, it is mainly controlled by the suction pressure. The movement of the slide valve is driven primarily by oil pressure, which in turn moves the oil piston. =============================== Premium promotions: Mechanical equipment——Summary of work done by equipment managers in 2017: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1881872 Mechanical equipment——Maintenance procedures for York screw compressors: https://bbs.hcbbs.com/thread-1806833-1-1.html Mechanical equipment——Upgrading of York Quinton control centers: https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment——Major repairs of GEA Grauso 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=
The flow rate of screw compressors is commonly regulated using a slide valve mechanism. This involves installing a slide valve that can move axially between the two rotors; by moving this slide valve, the effective working length of the rotors changes, thereby enabling energy regulation. The slide valve is in close contact with its fixing mechanism. When it is in the full-load (100%) position, all the gas contained in the groove volume is discharged. At partial load, the slide valve moves toward the exhaust side, and a bypass path is created at the suction inlet. Part of the incoming gas returns to the suction side without being compressed through this bypass path, resulting in a reduced effective working length of the rotors and only the gas in the groove volume being discharged. As the slide valve moves continuously, the energy is adjusted steplessly between 10% and 100%. The position of the slide valve can be controlled electrically or hydraulically. Automatic energy regulation is generally achieved based on changes in suction pressure or temperature, and the position of the slide valve can also be adjusted manually. At loads above 50%, there is an almost direct proportional relationship between power and air flow rate; however, when the load is below 50%, the performance coefficient drops significantly, resulting in poorer economic efficiency.
Regulation is achieved through suction pressure; as the slide valve moves, the elemental volume between the teeth of the compressor’s male and female rotors remains connected to the suction port via the return hole in the slide valve for a period of time before the tooth contact line shifts from the suction side to the discharge side. This allows some gas to flow back to the suction port, thereby changing the effective working length of the rotors and achieving energy regulation
The screw refrigeration compressor is a positive-displacement compressor that uses a slide valve to regulate the amount of energy. On the high-pressure side of the two rotors, there is a slide valve that can move axially relative to the screws; by changing the effective axial working length of the screws, it is possible to adjust the energy level continuously and steplessly between 100% and 10%.
The screw refrigeration compressor is a positive-displacement compressor that uses a slide valve to regulate the energy output. That is, on the high-pressure side of the two rotors, there is a slide valve that can move axially relative to the screws; by changing the effective axial working length of the screws, the energy output can be adjusted continuously and steplessly between 100% and 10%. This adjustment is made based on the value of the suction pressure or temperature.
It operates by using hydraulic pressure to move the slide valve and control mechanisms.
The adjustment process: the axial movement of the slide valve is accomplished through a hydraulic actuation mechanism, based on the suction pressure and temperature
Answer: 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 to control energy flow and enable unloading during startup. The principle of energy regulation using a slide valve involves the axial movement of the slide valve relative to the screw, thereby changing the effective axial working length of the screw and allowing for continuous, stepless adjustment of energy between 100% and 10%. Energy regulation is achieved through oil-driven control. An energy regulation solenoid valve assembly consists of four solenoid valves connected to corresponding oil circuits; the use of these four solenoid valves allows for control over the direction of oil flow, thereby enabling control over the back-and-forth movement of the oil piston within the cylinder. This in turn allows the slide valve to move forward and backward, thus achieving the purpose of increasing or reducing load.
To answer this question, one first needs to know what the function of this slide valve is. The slide valve is a device used to control the load of a screw compressor. So when is it necessary to control the load? Of course, it is when the cooling load is high. So what parameters can be used to indicate the size of the cooling load? It’s of course the compressor inlet pressure. When the load is high, more refrigerant evaporates, which results in a higher suction pressure; consequently, the slide valve needs to be opened wider. The control mechanism is to control the hydraulic oil feed rate