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What is the volume ratio? What’s the use of the volume ratio? Today, Gonglenghui will explain to you the application of volume ratio technology in York refrigeration units. If you have any questions, feel free to reach out to Gonglenghui! https://p3.itc.cn/q_70/images01/20211101/6adbbf35a13543ac959f29882b73e5ad.png 1. Volume ratio (Vi): In reciprocating compressors, the exhaust valve opens when the pressure inside the cylinder exceeds the pressure upstream of the exhaust valve. Since screw compressors are not equipped with exhaust valves, the location of the exhaust port determines the maximum exhaust pressure of the compressor. When the compressor is in operation, it is necessary to consider the relationship between the volume ratio inside the compressor and the volume ratio required by the system. In particular, the ratio of the solvent of the sealed gas at the end of inhalation to the volume of the gas at the end of compression (just before exhaust) is known as the internal volume ratio (Vi). At the same time, the evaporator determines the suction pressure entering the compressor, while the compressor’s exhaust port determines its exhaust pressure. Depending on the location of the exhaust port, the exhaust pressure of the compressor may or may not match the system exhaust pressure. Under certain operating conditions, if the specific volume ratio is too high, it means that the compressor’s exhaust pressure exceeds the system’s exhaust pressure; this over-compression leads to increased energy consumption, as shown in the figure below. https://p9.itc.cn/images01/20211101/86e02452665e42bcbe2522d1fe41f05c.jpeg Another scenario is when the internal volume of the compressor is too small; in this case, the exhaust pressure of the compressor will be lower than the pressure required for the system to operate, a condition known as under-compression. Under compression: the exhaust pressure of the compressor is lower than the pressure in the exhaust pipe, causing the high-pressure gas in the system to flow back into the rotor and increase the thread pressure. Of course, both under-compression and over-compression increase the system’s energy consumption, as shown in the figure below. https://p2.itc.cn/images01/20211101/407588b0fc0745028d8e9227f12f4f07.jpeg The ideal situation for a compressor is when the volume ratio of its components matches the volume ratio of the entire system, as shown in the figure below. https://p6.itc.cn/images01/20211101/fc720f4e313c4279a06aaf3badc7f0b4.jpeg II. Fixed volume ratio: Compressors with a fixed volume ratio are designed for applications where the operating conditions remain relatively constant. Since the volume ratio is fixed, the compressor can achieve its highest efficiency only when it operates under the designed conditions. Once the compressor operates outside its design parameters, it will result in over-compression or under-compression, reducing the compressor’s efficiency. In situations where system conditions are very stable, compressors with a fixed volume ratio can be used. As shown in the figure below, it represents a design with a low fixed volume ratio. https://p3.itc.cn/images01/20211101/15a6e7338d304a11adb74506f5410ab8.jpeg The following shows the design with a high fixed volume ratio. https://p6.itc.cn/images01/20211101/e7083476236548f5a6b70e3ef6f00409.jpeg III. Variable specific volume ratio: Compressors used in industry all employ variable specific volume ratio technology; the slide valves and sliders of these compressors can move simultaneously. The capacity control of the compressor is performed by a slide valve, while the volume ratio is controlled by a slider. The suction pressure and exhaust pressure of the system determine the position of the slider, which can be linked to the spool valve; when the slider moves, if the spool valve remains in the 100% position, it means that the position of the spool valve’s exhaust port changes. Changes in the exhaust port position alter the volume ratio within the compressor, thereby preventing over-compression or under-compression of the compressor. The movement of the slider can be controlled manually or automatically. When controlling the slider manually, engineers need to determine the compression ratio using calculation tables, and then move the slider by opening and closing valves. In manual control systems, the position of the slider is usually restricted to a few finite positions. When automatic control using a slider is employed, the computer or microprocessor calculates the slider position by determining the system intake and exhaust pressures obtained through real-time monitoring. Once it is necessary to change the position of the slider, the processor calculates the desired position and then moves the slider using the hydraulic system. Variable sliders are typically designed with a volume ratio range of 2.2–5.0 Vi. The diagram below shows how a compressor with a variable specific volume ratio changes the position of the exhaust port to prevent over-compression or under-compression of the compressor. To conclude, in order to ensure the long-term operation of the compressor, preventive maintenance is an absolutely essential measure. Since the compressor is part of the refrigeration system, the operation of this system is crucial for the compressor’s service life. If the compressor is not regularly inspected and maintained, it is very likely to stop working, which can disrupt production and create safety hazards.