The unified design of vacuum pumps does not always solve problems requiring high performance. Improving performance by increasing the elemental base also rarely justifies itself, affects the reduction in the durability of the structure and the stability of its units. The solution was a forevacuum pump, which provides an autonomous discharge function. As a result, the main equipment is able to work with optimal pressure indicators.
Principle of operation of the fore-vacuum unit
Vacuum pumping units operate with several pressure levels, passing from one state to another as work operations are performed. Forvacuum operates in conditions of a preliminary level of vacuum, which must be created using special plunger, mercury or steam-oil devices. The process of transition from one rarefaction level to another involves the use of appropriate methods of pumping the working medium, as well as measuring pressure. The most effective means of realizing this task is the foreline pump. The principle of operation of such devices is based on obtaining a preliminary or higher level of vacuum discharge.
The simplest model of this function is demonstrated by a vane-stator pump. This design provides for the rotation of the cylindrical rotor. The rotor with the plate divides the cavity into two parts: in the first, the working medium is compressed, and in the second, expansion. During operation, the fore-vacuum pump adjusts the pressure parameters, which is reflected in the main installation, to which the pre-discharge system is connected.
Main characteristics of foreline pumps
Like all other pumps, fore-vacuum units are characterized by the feed rate of the working medium and pressure indicators. As for productivity, it on average varies from 0.6 to 3000 m 3 / h. The pumping speed is determined by the volume of the vacuum chamber and the time required for its maintenance. Actually, this will be an indicator of productivity. Compression pressure is also taken into account. A standard foreline pump provides about 500 mbar. The operating pressure range in terms of minimum values is limited by the ultimate vacuum, which, in principle, is possible for a particular type of equipment. The upper limit is limited by the maximum pressure at the exhaust, upon reaching which the pump provides a vacuum at the inlet. In particular, oil-rotary models have a limit vacuum in the spectrum of 10-3 torr.
Varieties of designs
Several approaches are used to classify such aggregates. The most common division according to the principle of action is mechanical and physico-chemical models. An example of a mechanical rotary pump has already been considered, and now you can turn to examples of installations working with gas. So, for example, installations that provide a vacuum by changing the position of the chamber and periodically varying the volume of gas content due to the valve are isolated. An alternative to such devices is a sorption modification, which does not pump gas in portions, but binds it in the system. At the same time, both physicochemical and traditional oil-free fore-vacuum pumps differ in terms of operating pressure. So, there are models that work with low-, medium- and ultra-vacuum systems.
Pump manufacturers
The segment includes various companies that work both in the domestic niche and in meeting the needs of large manufacturing enterprises. For example, the Japanese company Anest Iwata offers fore-vacuum models with a range of performance indicators from 100 to 500 l / min. Also, model lines of dry pumps of this type are offered by the developers of Kashiyama. This company specializes in the production of high-performance equipment of spiral and screw type, which provides flow in volumes up to 3500 m 3 / h. At the same time, less powerful and inexpensive units with a capacity of about 5 m 3 / h can be found in the family. Edwards English forevacuum pumps, which implement the latest technology for pumping liquids, are also famous for their quality. The equipment of this brand has established itself in highly specialized areas. For example, Edwards pumps are used in instrumentation, chemical production, in enterprises that manufacture lighting lamps, etc.
Reviews of forevacuum pumps
Initially, the concept of fore-vacuum pumps suggested the possibility of eliminating the instability of conventional pumping structures. Modern optimized systems, supplemented by such devices, are already evaluated as a single installation for several indicators. Most of the positive reviews relate to the high performance of the equipment, the minimum level of noise and vibration. Accordingly, the service life of the main vacuum is also increased. On the other hand, the fore-vacuum pump is often criticized for introducing contaminants into the main pumping system. But this applies to oil structures, which are gradually leaving the market.
Conclusion
The principle of operation of the forevacuum is also considered obsolete. Supplementing the design of pumping equipment with another unit is contrary to the ideas of optimizing the size of equipment that modern manufacturers are striving for. Nevertheless, today there is no alternative regulator of pressure indicators that could replace the foreline pump. The price of such units, amounting to 5-10 thousand rubles. in the middle segment, also does not contribute to their distribution. However, provided that initial calculations of the system performance indicators are carried out accurately, many enterprises manage to effectively use the fore-vacuum. Another thing is that in the future it should also provide for the maintenance costs of this installation, in addition to the main pump.