This pump is used to circulate the liquid through the sparge pipe or eductors and also to pass the solution through a chamber by which Potassium Hydroxide flake can be dissolved for the purpose of maintaining the alkalinity of the stripper at the required level. Adding the Potassium Hydroxide directly does not produce satisfactory results and the addition of Potassium Hydroxide liquor is unsuitable as it contains at least 50% water.

For circulation, as a general principle, the greater the agitation, the more efficient will be the stripping process as stripped residues will be continuously scoured from the work surface, exposing a new surface to the stripper. Also, the stripped residues will be kept in suspension ready for filtration rather than fall to the bottom of the tank or coat the heaters.

Double diaphragm pumps have been found to be suitable for the following reasons:-

1. There is no shaft seal to be deteriorated by the stripper.
2. If the pump stalls against pressure in the system, it just stops rather than tripping out the motor or burning it out.
3. As they are air operated, there are no flameproofing considerations.
4. They are more tolerant of pumping sludges than pumps using impellers.