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Solenoid-operated diaphragm pump

With extended operating and setting options
Solenoid-operated diaphragm pump

The range of applications of the gamma/L metering pump extends from the stand-alone model in the laboratory to the bus-linked metering unit in complex systems. The calibratable pump allows the metered quantity to be displayed directly in l/h.

Michael Rummer, Holger Ludwig

The gamma/L series of metering pumps (Fig.1) represents a consistent further development of the tried-and-tested gamma/4 and gamma/5 series. The main aim of this development was to extend the operating and setting options of the pump, in order to be able to integrate it even more effectively in automated processes. The gamma/L, however, is also particularly suitable as an effective stand-alone metering pump for precision metering tasks in laboratories, for instance. It is supplied as a universal voltage unit that makes it possible to operate the pump with any supply voltage from 100 to 230 V AC.
The calibratable pump allows the metered quantity to be displayed directly in l/h, instead of calculating the metered quantity based on the set stroke length and stroke rate. The large, illuminated LC display en-sures that all displayed variables are easy to read up to a viewing angle of 45°. All the information belonging to the relevant operating mode can be called up by pressing the i-button. This provides increased security against mistakes both while programming the pump and while monitoring during operation in one of the four possible modes: manual, external contact, batch and analogue. The pump features an input for a two-stage, float-type level switch with an early warning function for the purpose of monitoring the supply of chemicals. When the supply of chemicals begins to run low, there is still sufficient time to top up the tank before the pump is stopped. A flow monitor can be connected for the purpose of registering each individual stroke. If the number of metering strokes defined for a specific process is not completed in full, an error message is triggered and can be reported via an optional relay.
Operating and control options
If the metering pump is operated in manual mode, the metering capacity is set manually based on the stroke length and stroke rate. In the case of external contact control via floating contacts, the stroke rate of the pump is defined by a control unit, for example a contact water meter or a Dulcometer mea-surement and control unit. The ratio of the incoming contacts can be stepped up or down within the range from 0.01 to 99.99 to facilitate optimum adaptation to the control unit. If the control contacts are entered faster than the pump can process the data, the corresponding data can be buffered with the memory function. Batch mode represents a variant of the external control function via floating contacts. In this case, it is possible to set batch metering either with a pulse ratio of 1 to 65535 strokes per incoming start contact or by pressing the P-button on the pump, optionally with a memory function.
Several variants of the analogue control option via a 0/4 to 20 mA signal are available. In the standard setting, the stroke rate of the pump increases proportionally to the in-coming current signal, in other words 0/4 to 20 mA corresponds to „0 to maximum stroke rate“. In addition, it is also possible to allocate the stroke rate to the input signal arbitrarily, thus enabling an inversely proportional characteristic and adaptation of the pump to the control signal. This permits the gamma/L to be used as a metering pump with an integrated proportional controller, representing a favourably priced alternative to conventional systems. In all operating modes the pump can be switched on and off with the pause function via a floating permanent contact.
Solenoid actuator
Figure 2 shows the structure of a solenoid-operated, diaphragm-type metering pump in schematic form. It essentially consists of the actuator (1) and the delivery unit (2). Solenoids (3) are used in two sizes (D70 and D85). The housing (4) is the same for both sizes. The gamma/L is based on a modular design, thus making it possible to cover the entire output range with a combination of two actuator sizes and eight different sized delivery units. There is only one moving part in the solenoid actuator, namely the thrust piece (5) which is guided in composite PTFE bearings. During the metering stroke, the diaphragm (7) is moved forward by the solenoid spindle (6). The intake valve (11) closes and the metered medium is displaced out of the liquid end by the discharge valve (12). The return spring (8) then moves the diaphragm back to its initial position, the discharge valve closes and a fresh quantity of chemical is drawn through the intake valve into the liquid end. The stroke length (max. 1.25 mm), and thus the stroke volume, is set by means of the stroke adjustment pin (9) and the adjustment spindle (10) by reducing the return stroke.
Range of materials
In all versions, the metering diaphragm consists of a plastic core integrated in a fabric-reinforced elastomer with PTFE coating, which is resistant to virtually all chemicals. The diaphragm is mounted between the liquid end (2) and the end disc, thus hermetically sealing the pump chamber from the outside and ensuring that the pump is leak-free. This arrangement makes it possible to pump metered media that is not allowed to come into contact with the atmosphere. A diaphragm failure signalling facility can be supplied, to round off the safety package.
Depending on the specific application, the optimum combination for the pump can be selected from the available range of materials. Polypropylene is used in water treatment processes. PVC is preferred for cleaning and disinfectant chemicals. Acrylic glass offers outstanding resistance to chlorine bleaching solutions and is a transparent liquid end material. This has the advantage that it is pos-sible to observe the pumping process in the liquid end, in order to detect and remove any air inclusions or crystalline deposits that might interrupt the metering process. Liquid ends made of PTFE are available for the purpose of metering highly concentrated or oxidising acids and alkaline solutions. Solvents and liquids containing oil can be metered most effectively with the stainless steel version. Metering pumps need to meet these requirements particularly in the chemical and chemical-pharmaceutical industries. Self-venting liquid ends made of polypropylene and acrylic glass are available for gas-emitting media.
Miniplant technology
In miniplant technology (Fig. 3), chemical processes are conducted on a small scale for the purpose of optimally matching mutual parameters such as reaction time, reaction temperature. concentration of individual educts and selection of the most efficient catalysts. In addition to the measurement and control systems as well as the apparatus set-up, the metering technology plays a decisive part in such systems. The gamma/L complies with a large number of the required properties, such as:
• control via a standard signal or field bus (Profibus DP V1 in preparation),
• display of controlled variables at the pump for fast monitoring of the metering process,
• compact dimensions and lightweight design,
• easy removal of the pump from the system, thus rendering disassembly of the apparatus unnecessary,
• low-wear actuator and long service life of the diaphragm,
• in the infeed at the suction branch, the pump can be used for level control in reaction apparatus by drawing off condensation water from the vacuum (up to 50 mbar depending on the pump size).
Measurement and control systems
With the analogue input option, the gamma/L can also be used as a metering pump with proportional control characteristics in control circuits with the measured value in the form of a 0/4 to 20 mA signal (Fig. 4). The „ower sideband“ and „upper sideband“ control variants should be selected for this purpose. Figure 4 shows two-side neutralisation. The measurement signal corresponds to a measured pH value between 2 and 12. The setpoint is pH 7. By selecting points P1(I1/F1) and P2 (I2/F2) it is possible to determine the setpoint deviation at which the alkali pump cuts in (I2). F2 is the start frequency at this point. The control slope and the maximum rate at which the pump is to operate are defined by P1. In the case of the acid pump, the same applies to points P3 and P4. This type of control represents an extremely inexpensive alternative to conventional systems, consisting of a controller and a pump, that can be used for simple control tasks. As these examples show, the gamma/L is suitable for a wide range of metering tasks thanks to its versatile operating and control options.
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