Moisture and Freezing in Pulse Jet Dust Collectors

The root of the problem comes from the fact that as you compress air the moisture holding capacity decreases. Compressors have after coolers in which most of the condensed water is removed before the compressed air enters the distribution system. The compressed air is usually a bit higher temperature than the ambient temperature. As it flows from the compressor to the machines some additional water will condense. Usually any large droplets will be collected in the air line filters before they reach the machines. There is still some moisture but it does not affect the operation of most machines. On other machines where this remaining moisture is undesirable or harmful, dryers are installed between the machinery and the compressor. On compressed air powered pulse jet collectors, the presence of liquid moisture in the pneumatic lines can have serious effects:

1. The water can collect in the compressed air manifold. When sufficient water is collected, it may “squirt” into the filter elements during a cleaning cycle. The drenching of the filter elements is intermittent, but the long term effect is higher pressure drop, more frequent cleaning and premature filter element replacement. Often the filter will dry itself from the exhaust flow through the collector. But residual effects from this wet dry cycling are cumulative. Cellulose cartridge filter elements are especially vulnerable as each wet cycle causes the permeability to increase and harmful effects are much faster.
2. If a collector is installed outdoors in below freezing conditions, even very small amounts of moisture droplets can condense on the diaphragms of air valves. The diaphragms will then stick to the seats of the valves and will not close. This will discharge all the air from the system, since typically 150 to 400 SCFM can be discharged through the valve. Since these valves operate with internal pilot ports, the valve will not close until the supply pressure reaches 25 psig. There needs to be an external shutoff to get the collector (and sometimes associated compressed air supply) back to an operating mode.

Quality Air Management has a two different products to address these problems:

• Manifold Tank Automatic Drain Valve System
• Thermostatically control compressed air manifold heater. This system will allow the collector to operate even when the compressed air dryer is malfunctioning by turning any liquid moisture to water vapor.

QAM also provides dust collector retrofit and consulting services to help resolve common problems that no one else seems to have found solutions.