|The MGA With An Attitude
SAND BLASTER, Siphon of Pressure Feed - TS-118A
On 10/4/2011, Clayton Kirkwood wrote:
"I'd like it if somebody knew the qualitative difference between a suction blaster and a pressurized blaster".
The most important feature of a sand blaster is that it requires a LOT of air flow. So if you have a small air compressor you will have short trigger time before you lose air pressure, and a long wait for the compressor to recover and build up pressure again.
A suction blaster uses a venturi in the spray nozzle to "suck" air up through the media pickup hose. In reality the blasting media is pushed up the hose by the pressure differential between atmospheric air pressure and the lower absolute pressure at the venturi. In simpler terms, the pressure available to move air flow and blasting media up the pickup hose is less than one atmosphere (less than 14.7 psi). As such, the suction blaster is limited in the amount of blasting media that can be picked up and delivered to the gun. It is useful for small jobs like a valve cover for instance, but cleaning a set of wheels to bare metal would take all day. It is commonly used with limited air supply, like a 1 or 2 HP compressor. The suction blaster can also be very cheap, so it may be a good deal for occasional use on small jobs.
A pressure feed blaster applies compressor air pressure to the media supply tank. It can apply up to 10x as much pressure on the media pickup hose, therefore supplying an almost unlimited amount of blasting media to the gun, very useful for big jobs. A pressure blaster will typically require a large amount of air flow. My fairly efficient 2HP belt drive twin cylinder single stage compressor can produce 7.5 cfm at 90 psi. This is enough to operate a small (Harbor Freight low-end unit) pressure blaster with about 50% duty cycle (one minute trigger time followed buy one minute recovery time for the compressor). It works for moderate size jobs like body sills, frame and suspension parts, as long as you have enough time to work with only 50% duty cycle.
If you are contemplating blasting an entire car body, frame and suspension parts, then you really should have a larger compressor. Minimum size compressor for continuous blasting would be 5HP belt drive 2-stage compressor (usually on a 60 gallon air tank). Even at that you might think it's a bit slow when processing half a square foot per minute for paint removal or 1/4 square foot per minute for rust removal.
For fast production blasting the sky is the limit for compressor size. A local franchise of Media Tech has a 75HP electric compressor on a 150 gallon air tank. Electricity to run it is something like $7 per hour, but the guy can clean a whole unibody car body to bare metal inside and out in about 5 hours. He would like a larger compressor to be more productive.