Double membrane pumps
For powdery bulk materials

Within the last years conventional double membrane pumps have been employed increasingly for the pumping of powdery bulk materials very successfully. The relatively slow and gentle discharge with a small air share and, at least partly, the suction mode of these pumps account decisively for this development.

The pumping of bulk materials with simple membrane pumps, which are mainly employed with liquids, does usually only work with fine powders with a relatively low bulk density. With such a pump only powder can be sucked that can generally be compressed and which reacts with a compact movement to the underpressure generated by the suction stroke. A prerequisite for the pressure discharge is that the bulk material reacts similarly to a liquid but exhibits the lowest possible degree of fluidification at the same time. Therefore the range of applications for these pumps is relatively limited with powdery bulk materials. A multitude of powders and mixtures show bulk densities of > 500 kg/m³ and partly bulk characteristics which do not allow discharge via simple membrane pumps. The clear advantages of being able to pump even such bulk materials led to the development of a special pump for powdery bulk materials based on the system of the membrane pump. Electro-pneumatically actuated butterfly valves were installed at the in- and outlets of the pump chambers and the pump cycle was controlled. Connections for controlled air supply and pressure control were established at suitable positions at the pump chambers and in the outlet area. With these measures the conditions were established under which it is possible to specifically control the pump and to prepare the bulk materials for pumping. The general flow direction through the pump was set from top to bottom in gravity direction. This contrasts with many other membrane pumps but this feature was chosen in order to reach a certain self-fluidification of the material when in free fall. The entire system is controlled by a programmable control system. Various adaptable programs allow an optimal adjustment to the respective materials and conditions. A controlled air supply is also given in order to keep the materials in a state where they can be pumped and in order to keep the gas share of the flow as small as possible. This is especially important with materials which are to have the smallest possible gas share, e.g. with inert gas and subsequent preparation procedures of the gas phase. The pressure discharge is used most effectively if the bulk materials flow freely into the pump via a directly attached container. Since in this case no suction is to be effected, the energy can be used completely for the displacement of the bulk material into the feed pipe by pressure discharge. In case the bulk material is to be sucked from several stations and pumped into several other stations, we have developed the powder pump with suction amplifier. The amplifier unit consists mainly of a container with connections for suction pipes at the back wall, an integrated filter unit and a subsequent blast. This unit is mounted directly onto the inlets of the pump chambers. The flow volume of these versatile compact devices is approx. 3 – 4 m³ for distances up to approx. 40 m with powdery bulk materials with bulk densities of approx. 1000 kg/m³. With optimal bulk materials and transport systems higher flow rates and longer distances are possible. The DASAG pump systems have conquered a remarkable position on the market within the last few years. They are often a part of complete systems for the transport of bulk materials in recycling, mixing and packaging plants, foremost in the building materials industry and they are often employed with sensitive procedures in the chemical industry involving powdery bulk materials.
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