Abrasive Blasting 101
A vacuum blower is critical, often undervalued and misunderstood components of abrasive blast cabinets. Vacuum Blowers are commonly used on small blasting cabinets for very limited use or very low cfm gun size. Vacuum blowers are only one type of blower class available but result in high static suction but very low cfm air movement.
When it comes to abrasive blast cabinets, air volume (cfm) and static suction are both very important and must be considered when choosing any blasting cabinet. What becomes critical is a high static suction rating measured in Inches of Water or Static Pressure, and this is the measurement used for all four basic blower classes with blower cfm performance.
Class I Vacuum Blower: a floor fan blower. These move lots of air but have very low static numbers.
A 1/3 hp floor fan can move 10,000 cfm, but don’t place it against the wall because it can barely stand the static resistance of bending air 90 degrees. As you can imagine, these blowers have low static numbers – usually lower than 0.25” – so even placing them next to a wall results in decreased air movement. Due to their weak performance, these blowers are never used for blasting cabinets.
Class II Vacuum Blower: a squirrel cage blower. These have lower cfm numbers and can’t pull air through simple cloth filter material. Because they are not very strong in suction, these blowers are seldom used on any but the smallest and least expensive cabinets.
A Swamp Cooler uses the Class II Blower impeller to move high air volume at low static numbers, but typically are slower in rpm or can’t be balanced at higher impeller speeds because of its many lighter construction weaker fan blades. If the air has to pass through any thing more than loose mesh wire filter, this kind typically used on stove vents, the static resistance results in very little air movement. A 1/3 hp class II blower might get you 1,000 to 3,000 cfm on a typical evaporative cooler.
A Class III Vacuum Blower: a radial blade blower. These blowers are used on almost all industrial dust collectors with both air volume and static suction numbers. They can be both direct drive and belt driven.
In a class III radial blower, a standard 1/3 hp motor gets you about 400 cfm at about 5″ of static pressure. A larger diameter radial impeller give you more bang for your buck and higher numbers.
ProTip: Class III Radial Pressure Blowers are used to meet Air Pollution Guidelines for a reason. They provide clean operation and good cabinet visibility with longer operation before dust collector cleaning is required, always a must do with Pollution Agencies.
A Class IV Vacuum Blower: a vacuum blower. These are great for moving very small air volumes and very high static numbers.
It takes about 1 hp to operate a 120 volt Class IV Blower, which requires 12 to 15 amps. Obviously 6,000 rpm impeller speed would make any blower pull higher static numbers, but you must not exceed 12 to15 amps on 120-volt power supply. This is what typically limits the size of any vacuum blower.
Most Class IV blowers would be much better on 220-volt power, which allows a larger vacuum and longer operation periods between servicing. In these situations, up to 10 hp vacuum blowers are available and are used for things like coin carriers you see at drive up banking facilities. These blowers are exceedingly well machined, balanced and have nearly no clearance or air-slip making both the horsepower and cost to operate very high. Remember, you cannot exceed 12 to 15 amps if you’re using only 120-volt power.
For a typical 120-volt vacuum, get the highest static rating numbers you can find but remember the key is amps used with static rating. Getting the highest static rating is key, but often blower manufactures hide those numbers. Know that static numbers over 100 inches are very common.
ProTip: air has weight and the more of it you move the more important is it to keep the blower impeller moving the air balanced.
As with most things, you get what you pay for investing in a vacuum blower operated dust collectors to operate any small blasting cabinet. Purchasing a cheaper Class I or II Blower on any blasting cabinet is not recommended. Spending a bit more up front on a Class III Blower for your Media Blaster will increase the static suction rating, which is measured in Inches of Water or Static Pressure, and is sure to pay off down the road and create great cabinet visibility. If you want to learn even more, check out these five tips about buying a vacuum blower.