Soft Scale Removal. Soft scale may be removed with a stiff bristle brush. After cleaning all scale particles should be
flushed out with water.
Hard Scale Removal. Hard scale can be removed by using a 10 percent solution of inhibited HCl. This acid solution is
available commercially or can be prepared using 20 parts water and 6 parts 30 percent HCI. Flush the part thoroughly
after using the acid solution. A 5 percent Sodium Bicarbonate Solution can be used to remove any acid left on the part.
WARNING: AVOID SPLASHING ANY ACID SOLUTION. WEAR PROTECTIVE CLOTHING AND AN EYE SHIELD
WHEN HANDLING CHEMICALS.
CAUTION: WHEN USING THE ACID SOLUTION, DO NOT ALLOW THE ACID TO REMAIN IN CONTACT WITH THE
PART FOR MORE THAN 20-MINUTES. UNDER NO CIRCUMSTANCES SHOULD ANY ACID CLEANER BE
ALLOWED TO COME IN CONTACT WITH TINNED SURFACES (SUCH AS, THE DISTILLED WATER SIDE OF THE
CONDENSER OR THE DISTILLED WATER TRANSMISSION TUBING).
NOTE: If inhibited HCI is not available, a 10-percent solution of sulfamic or acetic acid may be used as a substitute.
Exposure time to this acid is 2 to 3-hours. Sulfamic and acetic acids have an advantage over HCI; they will not corrode
the metal parts being cleaned.
Organic Scale and Sludge Removal. If the scale has a dark brown or black color, it may be formed from organic
impurities present in the feedwater. This type of scale may be removed with a strong detergent solution. The detergent
solution should be allowed to be in contact with the scale or sludge for 24-hours. Rinse off the parts with water after
Silica Scale Removal. Silica scale is usually clear and shiny and hard to detect visually. It is very hard and cannot be
removed with an acid solution. Silica scale formation can be reduced by controlling the quality of the feedwater by routing
it through a mixed-bed deionizer. It is best removed with a blunt instrument.
Biological Cleaning. Biological cleaning is used on the parts that come in contact with the distillate (such as, the
distilled water side of the condenser or distilled water transmission tubing) to remove biological contamination tubing
may be biologically cleaned by immersing the parts in a l-percent solution by weight of formaldehyde overnight.
Formaldehyde is available in 37-percent concentrations. After the required amount of exposure to the formaldehyde
solution, the still may be started and the distillate output may be used to rinse any remaining formaldehyde solution to
WARNING: AVOID SPLASHING THE FORMALDEHYDE SOLUTION ON OPEN CUTS.
NOTE: If formaldehyde is not available, lsopropyl alcohol is a satisfactory substitute.
DISASSEMBLY FOR CLEANING. The frequency of cleaning will depend upon the purity of the water being used. The
still should be inspected at frequent intervals until cleaning intervals are determined. Disassemble, inspect, and clean the
still as follows:
Stop the still.
Remove the condenser from the still. Inspect the cooling water side of the condenser for scale and clean as
Disassemble the evaporator until the interior of the evaporator is visible. Inspect the interior of the evaporator for
scale. Remove as much scale as possible manually.