Roots Vacuum Pump

Roots pumps are dry vacuum pumps used in low, medium, high and ultra-high vacuum systems to produce “dry” conditions.
The simple (single-stage) roots pump is most commonly employed as a booster pump for use in combination with several types of fore pumps (such as rotary vane pumps, screw and liquid ring pumps) to improve (or ‘boost’) ultimate pressure and pumping speeds. When multistage roots pumps are employed, no fore pump is required and they can operate from atmospheric pressure. A multi-stage roots pump can consist of up to eight stages and employ several sets of rotors (on a shared shaft). Roots pumps are suitable where a dry and clean atmosphere is important or, more likely, essential.

A Roots vacuum pump is a rotary positive-displacement pump with two symmetrically formed impellers rotating past one other in close proximity inside the pump case. A toothed gear synchronizes the two rotors, which have a cross-section that resembles that of figure eight.

Only a few tenths of a millimeter separates the rotors from the casing wall, as well as between the rotors themselves. As a result, Roots pumps may run at high speeds without causing mechanical damage. Roots pumps, unlike rotary vane and dry pumps, are not oil-sealed, hence internal leakage of dry compressing pumps by design limits compression ratios to 10–100. Internal leakage in Roots pumps, and other dry compressed pumps for that matter, is primarily caused by the working principle, which assigns specified surface areas of the pump chamber to the intake and compression sides of the pump.

These surface regions (rotors and casing) are loaded with gas (flow separation) during the compression process, and this gas is expelled during the suction phase. The clearance between the two rotors, as well as between the rotors and the casing wall, determines the thickness of the moving gas layer. It is not feasible to base one’s decision on the cold state because of the Roots pump’s rather complicated thermal conditions.

The structure of the Roots pump is shown as Fig. In the pump cavity, there are two rotors in "8"-shape, which are mounted in a pair of parallel shafts; they do synchronous rotary motion opposite to each other driven by a pair of gears at the transmission ratio of 1. There are some gaps between the rotor and the rotor and the pump casing wall, and can achieve high speed operation. As the Roots pump is a kind of vacuum pump, usually the compression ratio is very low, so the high vacuum pump need to backing pump. The Roots pump vacuum degassing depends on the pump itself structure and manufacturing precision, but also depends on the backing pump’s ultimate vacuum. In order to improve the pump’s ultimate vacuum, the Roots pumps can be used in series.

Similar Roots pump working principle and Roots blowers. Due to the rotor continues to rotate, was pumping gas from the suction aspiration to the space V0 between the rotor and the pump shell, and then be discharged through the exhaust port. The post inspiratory V0 space is completely closed state, so gas at the pump cavity no compression and expansion. But when the rotor turn at the top edge of the exhaust port, V0 space is connected with the exhaust side, due to the higher exhaust gas pressure side, some gas back washed to V0 space to the gas pressure suddenly increased. When the rotor continues to rotate, the gas discharged from the pump outside.

Also from the pump, in conjunction with the pump inlet to below the Roots pump rotor from 0° to 180° pumping process. At 0℃ position, left the rotor from V0 is sealed volume of gas. When turning to the Figure B, the chamber and the exhaust port are communicated. Due to the exhaust side pressure is higher, causing a portion of the gas back washed over. When transferred to the 90° position, a left rotor enclosed gas back flushing gas discharged to the outside. At this time, the right rotor pump inlet V0 is sealed volume of gas.

● Always check the oil level position shall be adjusted to conform to requirements of non-compliance when the pump is running to the Roots, the oil level to mark the center of the oil prevail.

● Drain intervals according to the actual conditions of use and the ability to meet performance requirements, etc. considered at the discretion of the user. Most of the new Roots vacuum pump, pumping gas when in addition to a clean, dry, oil change is recommended once in about 100 hours of work. Until the oil after you do not see a black metal powder can later be extended drain intervals.

● Always check the oil, the discovery of oil deterioration should be replaced with new oil, ensuring the Roots pump is working properly.

● In general, the Roots pump after 2000 hours of work should be carried out maintenance, inspection Jue rubber seals degree of aging, check the exhaust valve piece is cracking, cleaning deposits on the valve and the exhaust valve seat dirt. Cleaning the entire Roots pump chamber parts, such as the rotor, rotary vane, springs and other general cleaning with gasoline, and drying. after rubber parts can be cleaned with a dry cloth. cleaning assembly should be gently accidentally touch injuries.

● Bearing the body to join the bearing lubrication oil, observe the oil level should be the subject of the centerline of the oil, lubricating oil should be replaced or supplemented.

● Check the Roots pump tubing and junction without loosening. Rotate the Roots pump, take a look at the vacuum roots blower is flexible.

● Should be re-assembled after the test run, are generally required to empty running two hours and the second oil change, because cleaning the Roots pump would have a certain amount of volatile matter, to be operating normally, and then put to work.