Wobblerpump

Sammanfattning: The task was to design and manufacture a submersible displacement pump working with the wobble plate principle. The main task for the Wobble plate pump is to be used as a sewage pump for smaller households or dewatering pump in environments where small flows and high pressures are acquired. For these purposes ITT Flygt sell a screw pump, PC-Grinder 3068. The hydraulic part of the PC-Grinder is manufactured by a subcontractor. Therefore ITT Flygt wants to evaluate an alternative to their screwpump PC-Grinder, which can be entirely manufactured by them self. The specifications of the Wobble plate pump are supposed to match the specifications for PC-Grinder. The demands are that the Wobble plate pump is supposed to deliver a flow of 60 l/min, produce a head of 40 m, be able to function even if the water is contaminated by fibres and particles and share the same drivetrain as the existing dewatering pump 2610, produced by ITT Flygt. To match the demands in dirty water with particles and fibres requires a new grinder to be designed and constructed. The rotation speed for the Wobble plate pump was computed for a 4-pole electric motor but during testing a 2-pole electric motor was used. Therefore the rotation speed had to be decreased by using a variable frequency drive (VFD). The disadvantage of decreasing the frequency is that the heat losses in the engine increases and the engine shaftpower decreases. The result when running the Wobble plate pump with 25 Hz electric frequency is a maximum flow of about 42 l/min. The maximal measured head was 30 m but then the flow was as low as 9 l/min. The demands are not met because of the large leakages in the construction, but due to that the Wobble plate pump is just a first prototype, it can still be improved. Compared to PC-grinder 3068 the Wobble plate pump shows up to 15 % better efficiency. The grinder, which wobbles just like the wobble plate, has a unique grinding principle. This grinder design led to a patent application. The grinder test results proved that the grinding principle works and the grinder managed to grind fibres like wettex rags and toilet paper without clogging the pump. Further development of the Wobble plate pump can make it a good alternative to the PC-Grinder. In addition to better efficiency than the PC-grinder 3068 the Wobble plate pump might also be cheaper to produce.