Scroll compressor: principle of operation, advantages, choice
Scroll compressors are not cheap, as they are made with the mandatory requirement of minimum tolerances and high precision in the processing of elements. However, these devices have a lot of advantages that other types of superchargers cannot offer. Scroll compressors are extremely quiet and the air in the outlet path is absolutely oil-free. If we add to this the low cost of maintenance, it becomes clear why more and more individuals and companies are carefully researching the market for offering units of this particular class.
Device and principle of operation
The main working body, as follows from the name of the class of aggregates — Archimedean spiral. The compressor has two. One is static and fixed, it can be performed on the body elements, if we are talking about a device with an external drive. The second spiral rotates on the shaft. The principle of operation of the unit is as follows:
- during the rotation of the working spiral, there is no gap between its end and the walls of the stationary element;
- in the process of wrapping, a compression zone is formed, as it enters the center of the spiral, the air is compressed;
- the compressed working fluid is ejected into the output path.
This process is considered single cycle scroll compressor. It is repeated many times, since the number of revolutions on the drive shaft can reach thousands per minute. The compression process is stable, it does not have sudden pressure surges within one cycle, as happens in reciprocating compressors.
This operation scheme is implemented by shifting the axes of the spirals, working and stationary. It is called eccentric distance.
On a note! Some compressors provide for adjusting the displacement factor, both to adjust the outlet pressure limit and to provide a zero cycle without pumping.
Benefits of scroll compressors
One of the advantages of the scroll compressor, namely feed stabilityalready mentioned above. In practice, this means that there are no beats in the output air stream, which improves the operating modes of the consumer, for example, a pneumatic tool that operates with significant effort.
The user gets an additional benefit. Minimal flow beats and stable air supply means the scroll compressor is extremely quiet. In practice, the sound pressure indicator can be at the level of 5-10 dB, which is very valuable in medical equipment, air conditioning systems. In addition, scroll compressors have other advantages.
A scroll compressor with close to zero wear of antifriction seals that neutralize the gap between the working elements shows no loss of gas mass within one cycle. This opens the device wide range of applications in various dispensers. They are used in equipment for the preparation of gas mixtures with a controlled composition.
Zero dead volume
Reciprocating compressors have a dead volume characteristic. For spirals, this indicator is zero. The entire volume of the working block performs its functions with maximum efficiency.
Zero hydraulic losses
Scroll compressors (classic design) are oil-free, they do not have gearboxes and torque converters. As a result, all the energy transferred by the drive system goes to gas compression, without hydraulic losses in any operating modes.
Minimum heat transfer
When compressed, the gas heats up. If this heat is lost to the environment or related machine parts, it can affect the number of uses for the compressor. Spiral installations do not exchange heat with the environment.
[iframe width=»680″ height=»383″ src=»https://www.youtube.com/embed/wcIz6nd5UVA»]
Minimum friction loss
The only friction losses that exist in the compressors of this type are observed at the points of passage of the end of the working scroll, its contact with the antifriction seal. Their level is negligible. Therefore, we can assume that the total friction loss within the entire device is zero.
Simultaneous intake and release
The design of the compressor scrolls is such that during the working cycle (one revolution of the moving element), the moment of air intake and its release into the discharge path occurs simultaneously. This means that the drive motor can run in stable mode.without power take-offs.
The scroll compressor has no leakage, incomplete gas release or gap gas exchange (for example, the main losses in reciprocating units occur at the O-rings in the cylinder). Ideally, with zero seal wear, it shows transfer coefficient equal to 1.
Important! In practice, according to the results of experimental studies, a slightly lower coefficient was established. So, spiral installations show 0.92 at negative temperatures of -10 degrees Celsius, 0.94 at zero degrees, 0.95-0.98 at positive temperatures. In this case, the transmission coefficient is the higher, the greater the performance of the installation.
There are several other technological indicators in which scroll superchargers outperform competitors. In a philistine formulation, one can describe their advantages quite simply.
- Scroll compressors show a flow rate 20-30% higher than that of reciprocating units.
- At high temperatures (more than +10 degrees), they have 10-15% higher efficiency.
- Scroll compressors are very quiet, do not introduce impurities into the air, form a stable flow without noticeable steam pulsation.
[iframe width=»680″ height=»383″ src=»https://www.youtube.com/embed/ZvRHJdL4vLE»]
There are many varieties and models of scroll compressors. They differ in design features, type of work item, sealing level, basic purpose and other characteristics. There are one and two-stage devices, there are units of horizontal and vertical placement.
Compressors can have a classic Archimedes spiral, an involute element, a piece-circular and other configurations of the working body. There are fully sealed devices, glandless and non-sealed glands. There are dry compression units and oil-filled ones. Units differ in drive or power requirements, maximum outlet pressure, capacity, and cooling recommendations.
To choose the right scroll compressor, you should familiarize yourself with the range, prices, purpose and product characteristics. The last criterion is worth considering in more detail.
type of drive
The most common category of scroll compressors is equipped with an electric motor.. These are self contained devices. Today you can buy superchargers with diesel and gasoline engines. For some categories of users, the unit will be of interest, to which you can connect an external drive.
Torque transmission method
Today, the main gear in scroll compressors is belt (V-belt). But it has one drawback: over time, the belt stretches and can slip at times when the load and back pressure on the compressor sharply increase on the consumer.
More reliable toothed belt drive, but it requires fine tuning. Without this, the belt will not work out the prescribed service life. This type of transmission shows near-zero slippage and is worth the available money.
Gearboxes and others gear units the most reliable and durable, but they do not give freedom in installing the drive. However, if you want to get zero slippage under any load, torque conversion, predictable behavior and ease of maintenance, you cannot do without a gear transmission.
Wear of anti-friction seals depends not only on the characteristics of the scroll compressor. It is sharply increased by dust and other mechanical inclusions in the intake air flow. Therefore, despite the fact that the cleaning filter negatively affects performance, it is reasonable to consider a compressor with such a configuration. It will show the service life to the point of service, which is as close as possible to that declared by the manufacturer.
dynamic valve prevents backflow of air. For example, due to high pressure on the consumer side when the drive of the variable compressor is switched off. This node is optional, but it dramatically increases the predictability of the air injection subsystem as a whole.
Adjustable compressors, by changing the eccentric distance of the working and stationary scroll, allow you to adjust the maximum output pressure. In addition, blowers of this type are capable of operating in a zero cycle (ventilation) or without supply. Such an option would cost a lot of moneyhowever, in some compressor applications it can be very attractive.
The last thing the buyer should pay attention to is the material of anti-friction seals and their availability in retail.. In fact, this is practically the only part of the compressor that needs to be changed periodically.
Advice! When choosing a scroll blower, you should carefully study the manufacturer’s data, the indicator of the seals’ time between failures. It will not be superfluous to read the replacement instructions to see if it will be possible to carry out the work yourself.
Actually, the idea of a scroll compressor was realized only after the advent of friction-resistant materials for anti-friction seals. Therefore, when considering units of the middle and budget price category, when the manufacturer does not provide MTBF data or other useful information, you can focus on the year the model was released to the market. The fresher it is, the more likely it is to use reliable and durable anti-friction seals.
[iframe width=»680″ height=»383″ src=»https://www.youtube.com/embed/EJtjFN0xovc»]