The unified design of vacuum pumps does not always allow solving tasks that require high performance. Increasing operational performance by increasing the element base also rarely justifies itself, it affects the decrease in the durability of the structure and the stability of its units. The solution to the problem was a fore-vacuum pump, which provides an autonomous discharge function. As a result, the main equipment is able to work with optimal pressure indicators.
The principle of operation of the foreline unit
Vacuum pumping units work with several pressure levels, moving from one state to another as work steps are performed. The forevacuum works under 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 level of depression to another involves the use of appropriate methods for pumping out the working medium, as well as measuring pressure. The most effective means of realizing this task is the fore vacuum pump. The principle of operation of such devices is based on obtaining a preliminary orhigher vacuum level.
The simplest model for the implementation of this function is demonstrated by a vane-stator pump. This design provides for the rotation of a 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, it is expanded. During operation, the fore-vacuum pump adjusts the pressure parameters, which is also reflected in the main plant, to which the preliminary discharge system is connected.
Key characteristics of foreline pumps
Like all other pumps, foreline units are characterized by the speed of supply of the working medium and pressure indicators. As for productivity, it varies on average from 0.6 to 3000 m3/h. The pumping speed is determined by the volume of the vacuum chamber and the time it takes to service it. Actually, this will be a performance indicator. The compressive pressure of the working medium 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 exhaust pressure, upon reaching which the pump provides a vacuum at the inlet. In particular, oil-rotary models have a limiting vacuum value in the spectrum of 10-3 torr.
Varieties of designs
There are several approaches to the classification of such aggregates. The most common division according to the principle of action is mechanical and physico-chemical models. The example of a mechanical rotary pump has already been considered, and now we can turn to examples of installations working with gas. So, for example, there are installations that provide vacuum by changing the position of the chamber and periodically varying the volume of gas content due to the valve. An alternative to such devices is a sorption modification, which does not pump out gas in portions, but binds it in the system. At the same time, both physicochemical and traditional oil-free foreline pumps differ in operating pressure levels. So, there are models that work with low-, medium- and supervacuum systems.
The segment includes various companies that work both for the domestic niche and for the needs of large manufacturing enterprises. For example, the Japanese company Anest Iwata offers fore vacuum models with a performance range from 100 to 500 l/min. Also, model lines of dry pumps of this type are offered by Kashiyama developers. This company specializes in the production of high-performance equipment of spiral and screw type, which provides supply in volumes up to 3500 m3/h. At the same time, less powerful and inexpensive units can be found in the family with a capacity of about 5 m3/h. English Edwards foreline pumps are also famous for their quality.which implement the latest technologies for pumping liquids. The equipment of this brand has proven itself in highly specialized areas. For example, Edwards pumps are used in instrumentation, chemical manufacturing, light bulb manufacturing, and more.
Foreline pump reviews
Initially, the concept of foreline pumps assumed the possibility of getting rid of conventional pumping structures from instability in operation. Modern optimized systems, supplemented by such devices, are already evaluated as a single installation according to several indicators. Most of the positive feedback refers to the high performance of the equipment, the minimum level of noise and vibration. Accordingly, the service life of the main vacuum also increases. On the other hand, the foreline pump is often criticized for introducing contaminants into the main pumping system. But this applies to oil constructions, which are gradually leaving the market.
The principle of operation of the forevacuum is also considered obsolete. Adding another unit to the design of pumping equipment contradicts the ideas of optimizing the size of equipment, which modern manufacturers are striving for. However, today there is no alternative pressure regulator that can replace the foreline pump. The price of such units, which is 5-10 thousand rubles. in the middle segment, also does not contribute to their distribution. However, subject to the initial accurate calculationsperformance indicators of the system, many enterprises manage to effectively use the forevacuum. Another thing is that in the future, maintenance costs for this installation, in addition to the main pump, should also be foreseen.