Screw or piston compressors

Screw or piston compressors: the differences, which to choose, the best

The compressor is a machine that raises the pressure of gas or steam through the use of mechanical energy that is transformed into potential energy or pressure energy. Normally the compressors differ from the pump, since the latter acts as a fluid that cannot be compressed. 

There are 2 different categories of compressors: 

• VOLUMETRIC - in which the compression is obtained by varying the volume occupied by the fluid. 
• DYNAMICS - in which compression is obtained as a result of the speed that can be impressed on the fluid. 

Regardless of the pressure upstream and downstream of the compressor (that is, from the suction and delivery conditions), the volumetric compressors suck in a certain volume of gas. Normally they function in having a flow rate directly proportional to the rotation speed and a compression ratio totally independent of it.

In dynamic compressors or turbochargers, the fluid is compressed by exploiting the kinetic energy imparted to the gas by suitable mechanisms. Dynamic compressors are turbomachinery where the exchange of energy with the fluid takes place thanks to the rotation of a rotor (or impeller) keyed to a shaft, fitted to the periphery of blades and housed in a stator. The energy exchange between fluid and machine takes place in a rotating organ.

Among the volumetric compressors, the 2 most common types are:

• SCREW COMPRESSORS
• PISTON COMPRESSORS (also called reciprocating compressors).   

What is the function of screw compressors?

In screw compressors, 2 screws of different diameters with reverse pitch enter one another, thus creating a cavity that progressively moves from the suction area to the discharge area of the compressor body, thus compressing the gas. Compared to alternative compressors, screw compressors have the advantage of being composed of a simpler mechanism; the motion is continuous and, therefore, undergoes less impulsive mechanical stresses. The mechanical efficiency is superior to the alternatives. As a result, they are preferable for medium to large applications.   

The new generation of screw compressors also allow continuous power regulation thanks to the application of frequency variators on electric motors. In this way the unit is able to adapt its operation to any situation, ensuring maximum operating efficiency.

Screw compressors are also available with an integrated dryer, which guarantees the maintenance of air quality.   

The prices of screw compressors can vary greatly depending on the needs.

BOGE SCREW COMPRESSOR

BOGE screw compressors are characterized by efficiency, reliability and ease of maintenance. BOGE compressors are available in different types: oil-injected and oil-free coolers. The various models also differ in different types of transmission and possible adjustment by inverter. 

The main advantages of BOGE screw compressors: 

• Highly efficient operation that brings reduced energy consumption
• Production of continuous and energy-saving compressed air
• Pleasantly quiet operation. 

SCREW COMPRESSORS WITH OIL INJECTION COOLING

However different the C and S series may be, the screw compressor models are always highly efficient and cutting-edge. 

Here are some example products for the oil injection cooling category: 

• Screw compressor series C ... L up to 5.5 kW;
• Screw compressor series C ... FD up to 22 kW;
• Paintline screw compressor 5.5 up to 7.5 kW. 

OIL-FREE SCREW COMPRESSORS

Maximum reliability of BOGE screw compressors even when oil-free compressed air is required. The models are also available with air or water cooling. 

Here are some example products for the oil-free category: 

• BLUEKAT SLF series screw compressor up to 30 kW;
• SO series screw compressor up to 200 kW;
• SO 200 series screw compressor up to 355 kW.

What is the function of piston compressors?

With alternating compressors, compression is performed by a piston, inside a cylinder, in a reciprocating motion.An alternating compressor is a type of volumetric compressor, that is, a machine that uses the work carried out by a motor (which can be thermal or electric) to increase the pressure of a gas through a reduction in the volume the fluid occupies. It is usually used mainly in air compression, but also in process applications (for gases other than air), for example for methane and in processes related to the use/transport/extraction of other gases. It is also used to keep refrigerant fluids in circulation in air conditioning systems. In fact, piston compressors are widely used in the industrial sector.

Therefore piston technology is still used in industrial compressors.The air to be compressed is sucked into the cylinder through a suction valve, while the compressed air is expelled from the cylinder through the delivery manifold, and usually downstream of this, there is a tank that serves, in addition to performing the function of accumulation for the system, dampens the pressure pulses related to the reciprocating motion of the piston. Alternative compressors can be driven by electric motors or by internal combustion engines. 

Thanks to its simplicity, the reciprocating compressor is preferred to the other types for domestic use or for limited installed power. Almost universal in the use of air or refrigerant fluids, it allows compression ratios of 7: 1 - 9: 1 per stage. Consequently, it is possible to reach particularly high discharge pressures, for example in the charging of self-contained breathing apparatus, where with 3 or 4 stages more than 250 bar of pressure is reached. Also, it is used especially for high compression ratios and limited flow rates. 

Piston air compressors that require oil lubrication are generally not suitable for compressing clean air (eg for medical or instrumental use) due to traces of lubricating oil in solution with the pumped fluid required for cylinder lubrication and of the other mechanical parts of the compressor. However, there are "dry" models that do not use oil but are limited in compression ratios and require delicate maintenance.

BOGE PISTON COMPRESSORS

Whether oil lubricated or in the oil-free version, BOGE piston compressors offer optimal performance in continuous operation (S1 operation) and in the event of frequent load variations. They can also boast an exceptional quality/price ratio, long life and easy maintenance. 

The exclusive choice of high quality components, which allow to minimize maintenance costs and allow continuous use, is the secret of their high reliability and efficiency. For over 100 years, the robust BOGE piston compressors have represented the backbone of compressed air supply in craft enterprises and industry. The advantages of BOGE piston compressors: 

• Possibility of adaptation to individual needs.
• Continuous operation or frequent load variations.
• Pressures between 8 and 40 bar
• Long life and high reliability.

LUBRICATED OIL PISTON COMPRESSORS

Our piston compressors are an example of the proven BOGE quality: versatile and robust, they guarantee long life and reduced maintenance costs.

Examples of some oil lubricated BOGE pistons: 

• SRH piston compressor up to 11 kW. 
• SRM series piston compressor up to 15 kW. 
• Piston compressor series P ... L up to 1.5 kW. 

OIL-FREE PISTON COMPRESSORS

Thanks to the modular system these compressors can be assembled in customized systems, ideal in critical fields of application where high quality compressed air must be absolutely oil-free. 

Examples of some oil-free BOGE pistons: 

• K piston compressor up to 11 kW.
• PO ... LR series piston compressor up to 5.5 kW.
• ASO series piston compressor up to 3.2 kW.

So, better to buy a screw or piston compressor?

After having analyzed both screw and piston compressors in detail, we can say absolutely that in every sense there no better choice.  It always depends on how the machinery is used and also on the air flow rate the end user’s plant needs. 

Whether its industrial or domestic use, it's a good idea to rely on a real compressed air expert: BOGE. 

For over 110 years BOGE has been a reference point for those who want clean and reliable compressed air. Thanks to the high quality and efficiency of BOGE compressors and its compressed air solutions, it has gained the trust of over 100,000 users in more than 120 countries. The company was founded in 1907 and today has around 850 employees, of which 490 are employed at the headquarters in Bielefeld, a German city in North Rhine-Westphalia. BOGE, in fact, means German quality. Thanks to its intelligent design systems and innovative solutions that are always aimed towards the future, it has become one of the world's leading suppliers. The dense network of branches, service and sales partners, allow BOGE to be close to its customers to meet their needs, anywhere and at any time. The Air BOGE is the air you want to work with.