[Mechanical Equipment Technology Edition] Daily Question 20180404: Gas delivery volume control mechanism of screw refrigeration compressors (7)
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This post was last edited by YORK Industrial Refrigeration on 2018-4-8 at 10:11. 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 receive 10-15 points, with the validity period being two days. ============================== Screw refrigeration compressor gas flow control mechanism (7): What are the reasons for automatic loading and unloading of screw compressors? (Excluding electrical system issues) Answer: The four-way directional control valve has poor sealing, and the oil piston also has poor sealing. ============================== 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 Grasox 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=
1 First, it is necessary to check whether an increase in air consumption (or leaks) is causing frequent loading and unloading. If there is a blockage in the pipeline but it is not completely sealed, the flow of compressed air will be severely restricted. The gas pressure between the blockage point and the air compressor cannot be reduced quickly during the compressor’s loading phase, which results in the unloading pressure being reached after a short time and thus unloading occurring. Due to the limited volume of air between the blockage point and the compressor outlet, coupled with system losses (such as air in the filter drain line and during the regeneration of the cold dryer) and a small amount of air that flows to the air tank, the pressure drops quickly back to the loading pressure level, causing the compressor to start loading again. This cycle repeats itself. If it’s not the first situation, then it’s either a fault with the compressor’s pressure switch or with the inlet valve. 3 The pressure difference between loading and unloading is set too low; it should be above 0.5 MPa. The exhaust pressure of the air compressor is the main factor used to control its loading and unloading. If the difference between the two set values decreases, it may cause the unit to undergo frequent loading and unloading. When the loading pressure value of the unit increases, while the unloading pressure value decreases ； Either an increase in the loading pressure value or a decrease in the unloading pressure value will shorten the cycling time for loading and unloading of the unit. In other words, when the gas consumption of the unit remains constant, the closer the loading and unloading pressure values are to each other, the more frequent the loading and unloading processes become, which increases the risk of unsafe operation of the equipment. 4. The gas production capacity of the equipment is not proportional to the actual gas consumption by the users
The loading and unloading of the air compressor are primarily controlled by components such as the control computer, vent valve, intake valve, and loading/unloading solenoid valves. It is necessary to check each of these components individually, as well as to verify whether the installation locations of related components like the liquid separation tank are appropriate.
Exhaust pressure is too high; temperatures at various stages of the compressor are high
Automatic upload or automatic download. It is related to oil leakage from the oil piston. Or the directional valve is not sealed properly.
1. Large fluctuations in the amount of cooling capacity used on-site. 2. Oil leakage in the load adjustment system, resulting in an inability to maintain a constant load (these are the only two points that come to mind for now)
1 First, it is necessary to check whether an increase in air consumption (or leaks) is causing frequent loading and unloading. If there is a blockage in the pipeline but it is not completely sealed, the flow of compressed air will be severely restricted. The gas pressure between the blockage point and the air compressor cannot be reduced quickly during the compressor’s loading phase, which results in the unloading pressure being reached after a short time and thus unloading occurring. Due to the limited volume of air between the blockage point and the compressor outlet, coupled with system losses (such as air in the filter drain line and during the regeneration of the cold dryer) and a small amount of air that flows to the air tank, the pressure drops quickly back to the loading pressure level, causing the compressor to start loading again. This cycle repeats itself. If it’s not the first situation, then it’s either a fault with the compressor’s pressure switch or with the inlet valve. 3 The pressure difference between loading and unloading is set too low; it should be above 0.5 MPa. The exhaust pressure of the air compressor is the main factor used to control its loading and unloading. If the difference between the two set values decreases, it may cause the unit to undergo frequent loading and unloading. When the loading pressure value of the unit increases, while the unloading pressure value decreases ； Either an increase in the loading pressure value or a decrease in the unloading pressure value will shorten the cycling time for loading and unloading of the unit. In other words, when the gas consumption of the unit remains constant, the closer the loading and unloading pressure values are to each other, the more frequent the loading and unloading processes become, which increases the risk of unsafe operation of the equipment. 4. The gas production capacity of the equipment is not proportional to the actual gas consumption by the users
1. The intake valve is not open, so the compressor appears to be under load when in fact it isn’t; 2. The minimum pressure check valve is faulty; 3. There is a fault with the compressor unit itself
1. The variation in cooling capacity usage is large. 2. Oil leakage in the loading/unloading system prevents accurate weight setting. 3. Excessive exhaust pressure. 4. The pressure difference for loading and unloading is set too low.