What are rotary piston vacuum pumps
Rotary piston vacuum pump, full-name mechanical vacuum pump with oil seal of sliding valve, referred to as piston vacuum pump, is a variable volume gas transfer pump, the scope of application and conditions of use are basically the same as rotary vane pump.
Because of its structural characteristics, the capacity of the piston vacuum pump is much larger than that of the rotary vane vacuum pump, so it is more widely used in large vacuum equipment. The basic types of slide valve vacuum pump are also divided into two types: single stage and two-stage. The limit pressure of small pump in single-stage pump is generally not more than 0.6 Pa, the maximum pressure of large pump is not more than 1.3 PA (all closed town); the limit pressure of double-stage pump is not more than 0.06 Pa (closed town). The sliding valve vacuum pump with pumping speed over 150L/s adopts single stage.
Because the rotary mass of the piston vacuum pump has greater eccentricity, there is no good mass balance, and it will produce greater vibration when running. At the same time, it is difficult to realize the complete balance of inertia force of the sliding valve pump because the locus of rotation center of mass of the sliding valve pump is a complex closed curve. This limits the sliding valve type vacuum pump revolution, generally controlled in 350 ~ 600 R / min, individual can reach more than 1000 R / min.
The working principle of piston vacuum pump:
The main structure of the slide valve vacuum includes pump body, eccentric wheel, slide valve assembly and guide rail, etc. The driving shaft concentric with the pump cavity drives eccentric wheel to rotate, eccentric wheel drives the slide valve ring movement, so that the slide valve stem slides up and down on the guide rail and swings left and right. The slide valve divides the pump chamber into two parts: A and B. When the drive shaft rotates in the direction shown in the figure, the volume of cavity A increases and the pressure decreases, and the gas enters cavity A through the inlet and the slide valve stem (opening on the side of cavity A), which is in the process of suction. The sliding valve continues to operate clockwise to the upper left. When the volume of cavity A reaches its maximum, the inlet is isolated from cavity A, and the suction process ends. At the same time, the volume of cavity B is in the process of constant reduction and compression of gas. When the gas pressure of the B cavity reaches the exhaust pressure, the exhaust valve with oil seal is pushed away and the exhaust is started. When the slide valve is in the upper position, the exhaust end (A cavity volume is also at the maximum), a new round of cycle process begins.
The structural characteristics of piston vacuum pump:
The main structure of the piston vacuum pump includes a series of components, such as pump body, eccentric wheel, slide valve ring, slide rod, guide rail, etc. Similar to the rotary vane vacuum pump, the slide valve pump is equipped with an air ballast valve. The air ballast hole is opened near the exhaust port or on the end cover to exclude the gas containing condensable vapor, and an oil-gas separator is installed at the pump outlet to reduce the loss of pump oil and environmental pollution.
In addition to the distinction between single and double stage, the piston vacuum pump also has the distinction of single cylinder, double cylinder and three cylinders. The three cylinder slide valve pump solves the quality balance of the slide valve better, so that the vibration of the pump has been better improved, and the rotational speed is relatively high.
The main points of application of piston vacuum pump:
piston vacuum pump can be used alone as rotary vane vacuum pump, and can also be used as diffusion pump, oil booster pump, Roots pump and other vacuum pumps. Compared with rotary vane pump, sliding valve pump is more durable. It is widely used in vacuum coating, vacuum heat treatment, vacuum sintering, molecular distillation, aviation simulation experiments. . But in the case of water vapor, dust and other media environment, it is necessary to install a filter device, also can not be used for inflammable and explosive gas environment and compression of gas transmission. At the same time, limited by the characteristics of oil-sealed mechanical vacuum pump, in some areas of clean environment, such as semiconductor, petrochemical, applicability is inferior to some dry vacuum pumps.