Application

Compressed air production:
In the production of compressed air with reciprocating compressors, the system causes periodic pulsations to arise in the compressed air flow. This is caused by the expulsion of compressed air by the piston.

The basic frequency of the pulsation f0 can be calculated using the speed n and the number of compressions per revolution z of the connected positive displacement machine.

F0 = z x n / 60 [f0] = Hz

Here the periodic output amplitude can easily be 1 bar higher than the operating pressure (see fig.1)

The weak point:
Due to the reduction in volume, the air drawn in is nearly 100% saturated with moisture at the compressor outlet. To avoid corrosion and freezing in the compressed air network, the air must be dried downstream of the compressor. In the mobile field of application (trams, buses), the compressed air is usually dried by using single-chamber or double-chamber adsorption dryers, or, more rarely, membrane dryers.

a)     Adsorption dryers:
This drying principle requires a desiccant to adsorb the moisture. The moist compressed air flows through the desiccant which collects the moisture from the compressed air. The desiccant is compressed in the containers in the form of pellets, as bulk material. This prevents the pellets from grinding against each other and abrading. The grit arising from this, in the form of very fine dust, can lead to malfunctions of the equipment downstream.

b)     Membrane dryer:
This dryer principle works with the separation of gas mixtures (gas permeation). The process is based on the fact that different gases diffuse through membranes at differing speeds. For compressed air drying, membranes have been developed which have a layer which is highly selective for water vapour. This means that water molecules permeate/diffuse through the membrane faster than nitrogen, oxygen or carbon dioxide.
The membrane consists of special composite hollow threads; the supporting material (porous supporting layer) and the actual membrane separating layer (active separating layer) are made of different materials.

The physics:
The buffer volume between the compressor and dryer in the form of a short compressed air line is relatively small and thus cannot smooth out the discharge pulsation caused by the reciprocal compressor.

The damage:
a)     Adsorption dryer:
The discharge pulsation causes the pellets to move in relation to each other, and so become dusty, with the consequences mentioned above; the result is a considerable reduction in the service life of the desiccant.
b)     Membrane dryer:
The dynamic stress caused by the discharge pulsation wears down the membrane, considerably reducing its service life.
c)     A further point which must not be underestimated is the mechanical vibrations in pipelines and downstream components, caused by air vibrations, which can lead to leakages and vibration fractures.

The solution:
The Pulsmin team has developed vibration absorbers which can be used wherever machines or system components are jeopardized by pulsating flow rates.

The vibration absorber can also be supplied in combination with a pulsation damper.

Application for pulsation damper see application pulsation damper

See also scheme vibration absorber (PDF)