An Overview of Slide-Valve Vacuum Pumps

The slide-valve vacuum pump—fully known as the slide-valve oil-sealed mechanical vacuum pump—is, like the rotary-vane pump, a variable-volume gas transfer pump; its application scope and operating conditions are essentially the same as those of the rotary-vane pump.

Due to its structural characteristics, the slide-valve vacuum pump offers a much larger displacement than the rotary-vane pump, making it more suitable for large-scale vacuum equipment. These pumps are categorized into single-stage and two-stage types. For single-stage pumps, the ultimate pressure is generally no higher than 0.6 Pa for smaller models and 1.3 Pa for larger models (with the gas ballast closed); for two-stage pumps, the ultimate pressure is no higher than 0.06 Pa (with the gas ballast closed). Slide-valve vacuum pumps with pumping speeds exceeding 150 L/s typically employ a single-stage configuration.

Because the rotating mass of the slide-valve vacuum pump has significant eccentricity and lacks effective mass balancing, considerable vibration occurs during operation. Furthermore, since the trajectory of the rotating center of mass follows a complex closed curve, achieving complete balance of the inertial forces is difficult. This limitation restricts the rotational speed, which is generally controlled between 350 and 600 rpm, although some specific models can exceed 1,000 rpm.
II. Working Principle and Structure of the Slide Valve Vacuum Pump

1. Working Principle of the Slide Valve Vacuum Pump

The primary structure of a slide valve vacuum pump comprises the pump body, an eccentric, a slide valve assembly, and guide rails. Kelesi, a manufacturer of dry screw vacuum pumps, illustrates the pump's basic working principle below.

As shown in the diagram, the drive shaft—aligned with the center of the pump chamber—rotates the eccentric. The eccentric drives the movement of the slide valve ring, causing the slide valve stem to slide up and down and oscillate left and right along the guide rails. The slide valve divides the pump chamber into two sections: A and B. When the drive shaft rotates in the direction indicated, the volume of chamber A increases and the pressure drops; gas enters chamber A through the inlet and the slide valve stem (via an opening on the chamber A side), marking the intake phase. As the slide valve continues to move clockwise toward the upper-left position, chamber A reaches its maximum volume, the inlet is cut off from chamber A, and the intake phase concludes; simultaneously, the volume of chamber B continuously decreases, compressing the gas within. When the gas pressure in chamber B reaches the exhaust pressure, the oil-sealed exhaust valve is forced open, and the exhaust process begins. When the slide valve reaches the top-center position, the exhaust process ends (with chamber A at maximum volume), and a new cycle begins.
2. Structural Characteristics of the Slide-Valve Vacuum Pump

As shown in Figure 1, the main structure of a slide-valve vacuum pump comprises a series of components, including the pump body, eccentric, slide-valve ring, slide rod, and guide rail. Similar to rotary-vane vacuum pumps, slide-valve pumps are equipped with a gas ballast valve—with the ballast port located near the exhaust outlet or on the end cover—to facilitate the removal of gases containing condensable vapors; additionally, an oil-gas separator is installed at the pump outlet to minimize pump oil loss and environmental pollution.

The figure below illustrates the typical structure of a slide-valve vacuum pump.

In addition to the distinction between single-stage and two-stage models, slide-valve vacuum pumps are also categorized by the number of cylinders (single, double, or triple). Among these, the three-cylinder slide-valve pump effectively addresses the issue of slide-valve mass balancing, resulting in significantly reduced vibration and allowing for relatively higher operating speeds.
III. Key Application Points for Slide-Valve Vacuum Pumps

Like rotary-vane vacuum pumps, slide-valve vacuum pumps can operate independently or serve as backing pumps for diffusion pumps, oil booster pumps, and Roots pumps. Compared to rotary-vane pumps, slide-valve pumps are more durable and are widely used in fields such as vacuum coating, vacuum heat treatment, vacuum sintering, molecular distillation, and aerospace simulation testing. However, when operating in environments containing water vapor or dust, filtration devices must be installed; furthermore, they are unsuitable for use with flammable or explosive gases or for gas compression and transport. Additionally, due to the inherent characteristics of oil-sealed mechanical vacuum pumps, they are less suitable than dry vacuum pumps for applications requiring clean environments, such as in the semiconductor and petrochemical industries.https://www.btlasfilters.com/showproducts/productid/6320033/cid/637214/solberg-psg476-vacuum-pumpfilter03-micron/