A vertical oil-free screw vacuum pump with overpressure exhaust function

Abstract

A vertical oil-free screw vacuum pump with an overpressure exhaust function. The screw rotor adopts a double-head fully symmetrical variable pitch rotor, and its spiral lead gradually becomes smaller along the axis from the suction port to the exhaust port of the pump body; The compression ratio of the screw vacuum pump is set to R, R>3, R=V in / V out ,V in is the suction volume of the screw rotor at the suction port of the pump body within the 2π helix angle, V out is the exhaust volume of the screw rotor at the exhaust port of the pump body within a 2π helix angle; there is a pressure relief hole on the side wall between the suction port and the exhaust port of the pump body, and each screw rotor is provided with a corresponding A set of pressure relief holes, each group contains two pressure relief holes; a pressure relief chamber is provided outside the pump body, and the inner chamber of the pump body is connected to the pressure relief chamber outside the pump body through the pressure relief hole; the pressure relief chamber is connected to a pressure relief pipe , a pressure relief valve is provided on the pressure relief pipe, and the pressure relief pipe communicates with the exhaust channel of the pump body through the pressure relief valve or directly communicates with the atmosphere; when the gas pressure at the pressure relief hole is higher than the exhaust pressure, the pressure relief valve opens , the over-compressed gas is discharged.

Description

technical field [0001] The invention belongs to the technical field of oil-free screw vacuum pumps, in particular to a vertical oil-free screw vacuum pump with an overpressure exhaust function. Background technique [0002] The oil-free screw vacuum pump is a kind of dry vacuum pump with wide application. Depending on the way of expansion, screw rotors are divided into equal-pitch rotors and variable-pitch rotors. The lead of the variable-pitch rotor gradually decreases from the suction end to the exhaust end. Compared with the rotor, it also has many advantages such as less exhaust power consumption, low temperature, and low noise. [0003] For vertical oil-free screw vacuum pumps, most of them adopt the upper cantilever structure, so the screw rotor of the cantilever part must have good dynamic balance; for oil-free screw vacuum pumps with common single-head screw rotors, The center of mass of the screw rotor on each cross-section is in an eccentric position, so it has n...

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Problems solved by technology

[0007] ①. In the structural design stage of the oil-free screw vacuum pump, the compression ratio of the variable-pitch rotor is artificially controlled. The compression ratio is usually less than 2:1, which can achieve the purpose of balancing the power consumption of compression and exhaust. However, the disadvantages are also Obviously, first of all, due to the inability to achieve a larger compression ratio, the potential capabilities of oil-free screw vacuum pumps in terms of energy saving, cooling, and noise reduction will not be fully utilized; secondly, there is always an over-compression situation at high inlet pressure , and a high-power motor needs to be configured, which will not only generate large power consumption and high temperature heat, resulting in waste of energy, but also easily lead to failure

[0008] ②. During the operation of the oil-free screw vacuum pump, variable frequency power supply and variable frequency motor are used, and low frequency speed reduction is performed at high inlet pressure to control the pumping power. Although there is still overcompression at high inlet pressure, it can be Ensure that the motor will not be overloaded and heated. However, low-frequency slow-down operation will directly lead to a decrease in the actual effective pumping speed of the oil-free screw vacuum pump, thereby prolonging the pumping time at the high-pressure stage, resulting in reduced pumping efficiency and increased energy consumption.

[0010] However, in the above-mentioned patent application, the opening position of the overpressure outlet is not clearly set, which makes its operability in guiding the actual design worse, which is one of the main reasons why this technology has not been actually adopted so far. ; The above-mentioned patent application adopts the scheme of directly installing a spherical overpressure valve at the overpressure outlet, which is derived from the exhaust valve structure of various oil-sealed vacuum pumps, and the spherical overpressure valve is reset repeatedly by its own weight, but without Under oil conditions, it is very easy for the overpressure valve to fail to close tightly. Once the overpressure valve is not closed tightly, it will inevitably lead to backflow leakage into the pump through the overpressure outlet during the subsequent pumping process, resulting in pumping speed and The ultimate vacuum degree drops; moreover, when the spherical overpressure valve is opened, it will be accompanied by a lot of noise, which will bring adverse effects to the on-site staff; in addition, the multi-stage overpressure outlets of the above patent applications all pass The same independent connection channel is connected with the inner cavity of the pump, and the faults of "gas crossing" between the holes of the front and rear stages are very likely to occur due to the simultaneous opening of the spherical overpressure valve, resulting in the circulating flow of the pumped gas in the pump through the connection channel. In addition, the connection channel of the overpressure outlet of the above-mentioned patent application extends along the length direction of the entire pump body, which will inevitably affect the arrangement of the cooling water jacket of the pump body. If the cold water jacket is not well arranged, it will inevitably lead to a decrease in the cooling effect and a decrease in the temperature of the pump body. the rise of

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