Shortened design, inspection openings and robust material ensure safety and long service life at the same time as smooth conveyance. Roger Willis reports.
Storing or transporting larger amounts of 'live' explosives is always a huge risk. The development of emulsion explosives and mixes, such as ANFO (Ammonium Nitrate Fuel Oil), meant the creation of the possibility of storing the individual components of the explosive material separately.
The explosive is not mixed until it is on site, as soon as it is needed. Complicated and expensive storage of explosive which has already been sensitised can thus be reduced to a minimum.
The pump specialist NETZSCH has therefore developed special equipment for mobile mix loading vehicles to convey emulsified explosives. The progressing cavity pump has therefore been reworked to implement the necessary testing possibilities and safety measures. The two inspection openings which have been incorporated above the joints of the coupling rod are the greatest difference with respect to conventional designs. These mean that it is possible to check whether the joints are still sufficiently lubricated and the seals are still intact while the pump is in operation.
So-called K-joints are fitted for the connection parts themselves, which transmit the torque from the motor to the pump's rotor. These geared joints are different from pin joints in that they have a double seal and therefore provide increased safety: if one of the rubber sleeves becomes cracked, there is another one underneath which immediately takes over its tasks. This means that there is no way that oil can leak out of the joint. In addition, the coupling rod is drilled through, so that the joints can undergo a pressure test if necessary. If there is leakage of the pressure applied, this means there is a fault. The mechanical seals have been moved outwards, specifically for pressure equalisation, so that any possible overpressure can escape.
With this pumping principle, the stator and rotor together form chambers in which the medium is transported. Firstly, this means pressure-stable conveyance without any pulsation or shear forces. Secondly, the technology also allows the transport of filled materials, such as emulsion already sensitised with hollow microspheres. The length of the rotor-stator area has been specially shortened for this application. Longer pump bodies are used to increase the pump pressure, which needs to be avoided here.
The pump is set in motion using a hydraulic drive which is connected to a vehicle motor. We have deliberately managed without an electric motor, as the hydraulic system is space-saving and anyway power is not available on most building sites, or only to a limited extent. In terms of explosion protection, avoidance of sparking is ensured by the drive.
For more information at www.engineerlive.com/epe
Roger Willis is Manager Business Field Chemical, Pulp & Paper, NETZSCH Pumpen & Systeme GmbH, Waldkraiburg, Germany. www.netzsch.com