Dosing pumps in practical applications
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The Magdos is able to evaluate the level of chemical in the supply tank with remote indication by means of an alarm relay. Depending on the required service, the wetted end can be provided in different materials: PVC, PP, PVC, and stainless steels, i.e. 1.4571 (316SS). Check valves of different designs for suction and discharge side make the pump more efficient: double ball check valves for water-like media and springloaded ball valves for viscosities from 400 mPas (400 cps) on. Different kinds and sizes of connections are available for specific purposes.
dosing pumps of the Minidos and Memdos series are motor driven diaphragm dosing pumps. A single or three phase electric motor drives a single step worm gear. The gear translates the motor's rotating movement via an eccentric into a reciprocating movement of a plunger that moves the dosing diaphragm with a linear movement. The linear capacity adjustment at these pumps is achieved with a reduced plunger travel. Furthermore, the motor speed can be adjusted by means of a variable frequency drive.
More options
Another option is the electronic remote control of the stroke length. Here, it can be selected between either a three-point-step control or a control that receives an analog signal. A unique option of control is offered by the Memdos DX. It is equipped with a complete electronic control for the motor. Input control signals can be contact pulses, i.e. from a water meter, or analog signals from a controller or PLC. This pump control is also able to receive inputs from up to two level indicators. Via a dry contact the pump can output messages regarding the level of chemical in the supply tank as well as other operating conditions.
All larger diaphragm dosing pump models can be equipped with a double diaphragm system (Figure 3).
Double-diaphragm dosing head
An additional dosing diaphragm is placed in a chamber between the pump drive and the dosing head. The space between both diaphragms will be filled airfree with a neutral separation liquid. When the working diaphragm is in motion, the dosing diaphragm will follow, due to its hydraulic link via the separation liquid. If the dosing diaphragm fails, due to wear and tear, no process liquid leaves the system. The chemical mixes with the separation liquid that changes its conductivity. This change of conductivity is detected by a leakage sensor that sends an alarm to a remote control station.
Piston dosing pumps of the Fedos and Rekos as well as Kardos series are preferred, when pumping against high pressures and with high accuracy. The high accuracy of piston dosing pumps originates from a linear correlation between stroke length and capacity (Figure 4).
Piston dosing head
Pumps of these series are driven by single or three phase electric motors. A one step worm gear reduces the motor speed and generates the stroke movement. The piston dosing pump Fedos DX features an integrated electronic control unit for its motor. Incoming control signals in the form of pulses or an analog signal are proportionally converted into motor operation time and pump capacity.
Control features
This pump control is also able to receive inputs from up to two level indicators. Via a potential free contact the pump can output messages regarding the level of chemical in the supply tank as well as other operating conditions. The linear stroke length and capacity adjustment at the Fedos and Rekos dosing pumps is achieved with a plunger return limitation. The stroke length adjustment at the Kardos series is realizied via the change of eccentricity of the crank shaft. The same here, stroke length and capacity at these pumps can be adjusted via electronic remote control (notFedos DX), thus the dosing pumps can be used as active elements in a closed loop control circuit.
If abrasive or aggressive media have to be metered against high pressures, the advantages of diaphragm and piston dosing pumps can be combined. The piston diaphragm system KMS ensures a high accuracy of this dosing
task (Figure 5).
Piston-diaphragm system
With the KMS, the gear of a Rekos or Kardos is used as the drive for the stroke generation. Here, the plunger displaces a harmless hydraulic medium, i.e. glycerin. The chemical to be dosed is separated from the glycerin by a diaphragm. Depending on the stroke volume of the plunger a certain amount of glycerin is displaced. The dosing diaphragm is displaced by exactly this amount of glycerin. Internal valves secure the pump from an overload situation.
Diaphragm dosing pumps and piston dosing pumps can be equipped with multiple dosing heads. Their application may have several reasons:
• The capacity shall be increased.
• The maximum capacity shall be spread over several heads in order to meet high pressure requirements.
• The discharge pulsation is reduced. This is accomplished by the strokes of the different heads being set out of phase.
• If various media shall be dosed in parallel, the dosing heads are combined in a way that they work in phase.
• Chemicals shall be mixed in a certain ratio. Dosing heads of different sizes can be applied, their capacities fine tuned via each individual stroke length adjustment.
Dampening of pulsations
Due to the reciprocating character of diaphragm or piston dosing pumps, generated pulsations are carried through the chemical feed system by the discharged process fluid. At its peak a single head oscillating working dosing pump transfers approximately the threefold of its nominal capacity. That means a pump with a nominal capacity of 100 l/h (26.4 gph) discharges at a certain moment the maximum of 314 l/h (83 gph).
Pressure spikes are increased when long suction and discharge lines or small pipe diameters are installed. Improperly designed pipe systems may contribute to disturbed operation and even to damaged dosing pumps or entire chemical feed systems. Such problems can be avoided by a well designed system. (Figure 6)
Inline Pulsation Dampener PDS
One solution for this condition is the application of a pulsation dampener PDS. It is an effective means to smooth pressure spikes to a harmless level. The pulsation dampener stores a portion of the discharged flui