With regard to life cycle costs and the energy efficiency guidelines that will also be extended to motors with other designs and smaller capacities in the future, dosing pumps with a high overall energy efficiency are already in demand today. Lutz-Jesco is responding to this need. In contrast to conventional motor diaphragm dosing pumps in the capacity range from 4 to 1000 l/h, the Memdos LP series features an EC motor as an electric drive.
Memdos pumps are especially designed for applications in industrial processes where low pressures and high dosing quantities prevail. Thanks to a robust ram actuator with manual or automatic power adjustment, the conveyed media are dosed reliably and precisely. The pumps operate without leakage, even if the dosing diaphragm is worn, and are also suitable for highly aggressive and toxic chemicals. Dosing pumps with a double membrane system are optionally available. Depending on the type of gear, the diaphragm allows pressures up to 16 bar. The dosing quantity can be doubled by using two dosing heads per pump.
Memdos pumps are available in PVC, PP, PVDF or stainless steel for the dosing head and valves. In addition, there is a wide range of accessories for each pump, from the appropriate suction line through pulsation dampers to injection points, to meet almost any performance and resistance requirements. The possible dosing capacities extend from 0 to 4 and from 0 to 156 l/h in the first size or from 0 to 114 and from 0 to 1020 l/h in the second size. All versions are characterised by robust quality and permanently reliable dosing results. A selection of motors for hazardous areas (Atex) rounds off the portfolio.
Energy efficient design
Classic motor diaphragm dosing pumps with capacities between 4 and 1000 l/h have a three-phase asynchronous motor as an electric drive. However, the electrical output of these drives is usually below the limit of 0.75 kW specified in IEC 60034-30 and are thus not covered by the standard. Nevertheless, as mentioned above, this topic is becoming increasingly interesting for dosing pumps. Memdos LP motor diaphragm dosing pumps from Lutz-Jesco have an EC motor as an electric drive instead of a three-phase asynchronous motor with an external frequency converter. An EC motor is a brushless DC motor with its own power and control electronics. Commutation – the alternating energization of the individual stator phases – is effected via semiconductor elements and not mechanically by means of carbon brushes, as is the case with standard DC motors. As a result, the service life is significantly longer, similar to an asynchronous motor, and so-called brushing fire is avoided; especially at high speeds, this leads to increased brush wear and can cause electromagnetic disturbances due to feedback. Apart from the motor bearings, therefore, there is hardly any mechanical wear.
The rotor is equipped with a permanent magnet. This provides a lower rotor inertia compared to a standard DC motor as well as increased motor dynamics and more compact outer dimensions. To enable the current supply to be switched to the motor as a function of the rotor position, the motor has a sensor system which can detect the actual position of the rotor. Speed control is likewise possible. Due to the type of current supply, high torques can be achieved with an EC motor even at low rotational speeds. The motor has greater than 90 % efficiency. A three-phase asynchronous motor of the IE3 type, which is comparable in terms of performance, has efficiency better than 82 %. If the drive is to have a variable speed, a suitable external frequency converter must be included in the calculation. The EC motor, on the other hand, is inseparably connected to its power electronics due to its design, with which it forms a unit for the purpose of determining the efficiency.
The EC motors installed in the Memdos LP have one of three power ratings (250, 550 or 650 W) depending on the model. In the models with a 250 or 550 W motor, cooling is by means of free convection, in other words without additional fans, for even greater efficiency. Furthermore, the Memdos LP can be operated permanently at low flow rates, without the need for an external fan, as is sometimes the case with motors with an external frequency converter.
All-in-one concept
Since the power electronics and motor package form a single unit, they are both installed in one housing, giving the pump a clear design. Theoretically, the working torque is available at even very low speeds. Owing to the principle whereby filling of the dosing head is ensured at all times, the Memdos LP switches from start to stop mode above a lower limit speed. This limit is less than that of a motor with an external frequency converter because the torque starts to fall at a threshold equivalent to approximately 30 % of the maximum speed. The continuous monitoring of the sensor by the pump drive gives the Memdos LP very good dynamics, which is why it is suitable for high-precision dosing applications in conjunction with harmonised dosing heads, diaphragms and valves. The HP (High Performance) variants mentioned here are particularly interesting: they feature a brand new TPU diaphragm which facilitates an increase in output of more than 30 % as well as permanent backpressures of up to 16 bar with the same combination of motor and gearbox. This means not only a longer service life but also increased efficiency on the hydraulic side.
From a purely economic point of view, three-phase asynchronous motors still have advantages if the pump speed does not need to be variable. If there are no drive electronics in the form of a converter, the cost will be lower. The Memdos LB version, which combines the proven motor concept with manual stroke length adjustment, was developed for this purpose.
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Dr. Hans-Joachim Diederich
Business development, Lutz-Jesco
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