This pump is used to circulate the solution via the filterpress: a pump capable of producing 6 bar pressure is required. 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.