Air Sparger Design
The perforated pipe can be made of any material compatible with the solution and
temperature involved, PVC being most common. The usual design calls for holes on about 4-
to 6-in. staggered centers as shown in Fig. 4; the specified hole size is usually 3/32 to I/8 in.,
since smaller holes may plug too easily. An alternative to the traditional hand-drilled spargers is the newer porous pipe designs, which can save a lot of fabrication effort.
In order to promote even distribution of air along the sparger, it is important that it be
installed in a level plane and that the cross-sectional area of the pipe be larger than the
combined area of the holes. Pipe sizes as small as 1/2-in. diameter may meet this latter criteria,
but for most production-size installations, it makes sense to use a minimum pipe size of 1 in.
for mechanical rigidity.
General solution homogeneity is virtually assured with even a single air sparger, so rarely
is more than one used in a rinse tank; however, preventing ion depletion or gas accumulation
at the cathode of a plating tank may require multiple lanes of air spargers for full coverage,
since the air tends to rise almost straight vertically and a single air pipe is usually credited with
delivering only a 6-in. wide swath of generous local agitation.
Plastic pipes charged with air will have enough buoyancy to float, so they must be
secured to the tank bottom or equipped with plastisol-coated metal weights. It is often
recommended that the air pipes be positioned well off the bottom of the tank to minimize
disturbance of accumulated sludges, but in reality the pipes m'e invariably set directly at the
tank bottom.
To preclude the possibility of solution siphoning out of the tank when the air supply is
shut down, a small hole should be drilled in the riser, an inch or so above the solution level.