Paul McGregor from Airtight Solutions gives a few pointers on selecting the right bag machine for maximum performance.
Many portable systems claim high CFM or air volumes but this performance depends on minimal resistance in the duct layout. The type of waste that goes through the duct also has an impact on performance. For instance, fine dust will very quickly block ﬁlter material and may even pass through it, but light or large ﬂuffy dust may cling or stick to the filter fabric instead of dropping into the bins. Many installations end up with far more connections than they were originally designed for, diluting the performance throughout all the machines.
Dust extraction is not rocket science; however certain rules do apply and ignoring or pushing those limits generally results in poor performance. Many portable DC units work well in the beginning but lose efficiency over the following months.
Rule number 1:
You can never have too much ﬁlter area, however you can deﬁnitely have too little.
The more filter area a system has, the less back-pressure (restriction) will be created, resulting in greater suction (air volume) at the business end. A dust collector with 24 filter socks measuring 220Ø and 1.35m long will have more than twice the filter area and less resistance, compared to a similarly sized unit with 4 filter bags of 500 dia. and 1.5m long. Both units use a 3000rpm 10hp (7.5kW) fan. The one with the least resistance will perform much better and work over a longer distance, and the filter fabric will last longer. These units can also easily be modified for outdoor use or as pre-filters.
Rule number 2:
Good extraction is a balance of horsepower, resistance, DC design and ﬁlter area.
Applying more horsepower into the same ﬁlter area won’t help; it just forces the dust faster through the ﬁlter material. Eventually dust either blocks the holes in the fabric creating restriction, or bleeds through the fabric. Horsepower is wasted when there is resistance. Reducing resistance increases airﬂow, and is done by using efﬁciently designed fans, correctly sized short duct runs with the least amount of bends possible, short lengths of ﬂexible hose, slide gates to concentrate performance, and a dust collector with as much ﬁlter area as possible. The fabric must be cleaned regularly.
There are many portable bag machines available on the market with similar appearance and function. Where they differ is in the design and quality of the fan and the amount of ﬁlter area.
One proven alternative is a multiple ﬁlter sock unit that will enhance performance with increased ﬁlter area, heavy duty fan construction and high efﬁciency impeller.
The dust collector is only part of the equation. Efﬁcient ducting design, slide gates and quality, anti-static ﬂexible hose, all contribute to delivering the optimum solution. Inefficiencies in small portable units can reduce performance considerably. It is optimistic to expect cheap massed produced systems made from lightweight metal and basic fabric to cope efﬁciently with some of the modern requirements and volumes some machines need these days.
It’s like using a fabric gazebo instead of a garage to protect a prized car. They will both protect it from the elements and environment; one simply does it better than the other.