Subject Area

Systems Engineering / Pressure Equipment

Start


Virtual Exhibition presents:

Please click on the Logo to open the company presentation in our Yellow Pages.

Virtual Exhibition


PED Professional 6

Compressed Air

Everything you need to know about compressed air:
summarized by netinform and our partner BAUER KOMPRESSOREN GmbH München

Compressed Air
Compressor Types
Compressor Installation
Laws, Regulations, Technical rules
Types
Types

Compressor types



Contents by
BAUER KOMPRESSOREN GmbH München
Classes
Classes

Division of compressors into two major categories

Displacement compressors
In displacement compressors (reciprocating and rotary compressors), a static pressure is built up by means of a part that moves within a closed space such that it successively draws in air, compresses it and then discharges it again.

Dynamic type compressors
In dynamic type compressors (turbo axial and radial compressors or ejector compressors), a pressure rise is obtained by one or several rotating impellers accelerating the intake air to a high velocity, the kinetic energy then being converted into pressure energy in a diffuser. In this context, it must be noted that the turbocompressor's output is dependent on the operating pressure, whereas the dynamic compressor's output is not influenced by the operating pressure, unless leakages within the compressor and volumetric efficiency change. This information was compiled by our partner BAUER-KOMPRESSOREN and refers to their compressor types, namely multi-stage, air-cooled displacement compressors. Generally, these compressors are categorized in two groups:
     
  • oil-free compressors
  •  
  • oil-lubricated compressors

The compressors comprise between 3 and a maximum of 5 compressor stages (200-500 bar).

Contents by
BAUER KOMPRESSOREN GmbH München

Application
Application

Piston and cylinder configurations

At BAUER KOMPRESSOREN, three basic cylinder configurations have proved suitable both in theory and in practice.

a) W-type
b) star type
c) T-type

W-shape piston configurations are used mainly for smaller high-pressure compressors which need to be compact, lightweight and portable. They are readily accessed from all sides, which is an advantage when it comes to servicing. These compressor series, designated Vertikus 5, are used mainly in diving equipment but also in industrial plants.
Star- and T-type piston configurations are used in larger compressors both in the breathing-air and the industrial sector. The T-type configuration is used primarily in the industrial sector. Balancing of masses is excellent. First-order forces are thoroughly balanced. Each of the designs guarantees smooth, vibration-free running.






Contents by
BAUER KOMPRESSOREN GmbH München
Multistage compression
Multistage compression

Multistage compression

If, for example, the counterpressure and thus also the pressure ratio p2/p1 in a single-stage compressor is increased, compression decreases. The compressor's volumetric efficiency decreases, piston forces increase and since compression is almost isentropic under maximum cooling of the cylinder, the final compression temperature rises. As the temperature increases, oil lubricity decreases and there is the risk of partial oxidation on contact with air, which would result in the breathing air becoming contaminated with CO or too much CO2. Last but not least, the ratio of real to ideal, isothermal compression work becomes less favorable. As soon as it exceeds a certain value, therefore, the pressure ratio is divided up into several stages and the gas is cooled down after every stage, if possible back to the intake temperature. However, since flow losses and the purchasing price of the compressor rise as the number of stages increases, there is a limit to the number of stages possible.

Contents by
BAUER KOMPRESSOREN GmbH München

Cooling
Cooling

Compressor cooling

The heat generated during compression must be dissipated. Both cylinders and intercoolers must therefore be cooled at every stage. Depending on the manufacturer standard, this is done either with cooling air or water. Water-cooled compressors are very compact and also much more expensive than air-cooled compressors since air is available free of charge and this type of compressor does not involve the risk of the cooling water freezing. One or a maximum of 2 axial fans provide the compressor block with the necessary cooling air. In the case of smaller diving compressors, this is effected by a radial fan integrated in the flywheel. Since all the cylinders and intercoolers are positioned directly in the cooling-air flow, optimum cooling is achieved. In air-cooled compressors, the discharge temperature of the compressed air is approx. 5-10°C higher than that of the intake air. Permissible ambient temperatures for the air-cooled compressors range from between 5 to 45°C. If a compressor is installed outdoors, the entire compressor must be heated if the temperatures drop below zero.

Contents by
BAUER KOMPRESSOREN GmbH München
Lubrication
Lubrication

Compressor lubrication

Splash lubrication is the simplest lubrication method. A pin, which is attached to the crankshaft, dips into the oil each time the crankshaft rotates and sprays the bottom of the pistons and the cylinder walls. The oil spray mist that is formed also ensures lubrication of the rotating parts within the compressor. The prerequisite for effective lubrication is an almost horizontal position of the compressor. Splash lubrication is used mainly in small reciprocating compressors, which are only operated intermittently and, in addition, should also be portable. It works regardless of the direction of rotation. The best system of lubricating the moving parts in a compressor is pressure lubrication by means of an oil pump (low pressure approx. 3-4 bar). This type of lubrication is independent of the oil level in the crankcase. In contrast to splash lubrication, this method allows the compressor to be positioned at angles of up to 20°, depending on the model. Mineral or synthetic oils are used for lubrication. Synthetic oils are recommended for heavy-duty compressors in around-the-clock operation. The oil should be changed at the following intervals:
     
  • 2000 h for synthetic oils
  •  
  • 1000 h for mineral oils

Further details are provided by the manufacturer's technical customer service.

Contents by
BAUER KOMPRESSOREN GmbH München

Condensate drain
Condensate drain

Automatic condensate drain of oil and water separators

Depending on the temperature and relative humidity, the clean ambient air sucked in by the compressor contains an exactly defined amount of water. Since, during compression, the volume of compressed air decreases after each stage and the air is completely saturated once it has passed over the intercooler, condensate develops which must be drained off after each stage together with any liquid oil. This is effected by an automatic condensate drain added to the compressor block, which also includes an integrated device to depressurize the compressor at startup. In Bauer compressors, for example, the drain interval for the magnetic valves which drain the individual separators via condensate valves is set by BAUER B-Control, a freely programmable electronic compressor control system including a display. In larger compressors, separators are drained individually one after the other. The condensate in the separators of the small diving compressors may either be drained manually or, in line with the cascade principle, automatically via a time relay.

Contents by
BAUER KOMPRESSOREN GmbH München