Wherever condensate precipitates, this must also be disposed of. For this purpose, automatic condensate draining systems have been developed. These can be divided into mechanical float valves and electrical or electronic condensate drains.
Figure 4.11.1.1
Float valves, Fig. 4.11.1.1, must be specially adapted for the requirements of compressed air condensate, as this is an emulsion of water, oil and dirt particles, representing a much more critical operating problem than steam condensate. Precipitated condensate is collected and the buoyancy force of a float used in order to open up the valve seating. Because the buoyancy force is limited by the envelope size of the float, valve diameters of 0.5 - 2 mm can be designed. The stroke length of the valve stem is about 25-50% of the seating diameter. While system conditioned problems are pre-programmed, it cannot be denied that float valves do not alwaysfunction. The causes can be:
- Viscous emulsion,
- Accumulation of dirt or resinous material or stiction.
Draining by means of solenoid valves offers an alternative. Via a time control, these are opened for 1 - 10 seconds at specific intervals to dispose of the condensate. However, condensate accumulation in compressed air stations is not always constant and changes continuously. In contrast to float valves, each opening operation causes the unnecessary loss of compressed air. Apart from the fact that malfunctions are not indicated, another aspect has to be taken into account. Through the high velocities arising inside the solenoid valve, combined with several changes in the direction of flow, the oil particles contained in the condensate are broken up into micro particles and charged negatively through friction with the air. As a consequence of this, stable emulsions are formed, the processing of which is costly.
Figure 4.11.1.2
An optimum, reliable solution of condensate draining problems is provided by the use of level controlled electronic drains (Fig. 4.11.1.2). With this separator, the condensate is detected by a level sensor system fitted with contactors. As soon as the condensate level, reaches a contact, the electrical control system of the drain will open the solenoid valve (item 3) and direct the condensate away via a riser tube without loss of air. The condensate level is lowered and reaches a sensor, causing the solenoid valve to close. If sensor is not reached in a preset time, the controller sends signals causing repeat cycles of fixed duration. This ensures that the condensate collecting chamber is emptied completely. A sensor causes the control system to emit the principal alarm if opening intervals remain constant. This prevents any possibility of flooding of the system. As this level controlled drain operates with a time dependent cleaning cycle, there is no danger of "dried up" condensate, even if there has been a long period of non operation.
