Notebook 1 : What is a dosing or metering pump?
Metering pumps differ from other forms of pumps in that they are designed to operate with a high level of repetitive accuracy while being able to dose a wide variety of chemicals including acids, bases, corrosive or viscous liquids and slurries. They are positive displacement and they have the ability to vary capacity manually or automatically as process conditions demand and are driven by electric motors generally although other forms of drive are also available, such as air and water.
Piston Diaphragm Pump
Depending on the application the drives can be fixed or variable speed drive and they usually come with an additional stroke capacity adjustment either manual or actuator operated. Some applications dictate fixed speed and controllable capacity adjustment, which is achieved by means of the actuator fitted to the stroke mechanism. It is also possible to apply both variable speed and stroke variation to pump capacity control.
Overview of assemblies:
An interesting development is the water driven dosing pump which, as it is driven by the flow to be dosed provides proportional dosage to flow without the added complication of adding flow measurement systems.
Rotados
The rotary motion of the motor is translated into a reciprocating movement by the drive mechanism or gearbox. In the case of sera pumps this is a robust, gear-oil filled gearbox giving exceptional reliability and economic operational performance. Both ‘modified-cam and slide-crank mechanisms are employed and their use is dependant on pump capacity. Usually slide-crank above 1.1kW motor size.
Pump capacities may be increased while retaining required system pressure by adding additional pump heads. This also has the potential to smooth delivery especially if an odd number of heads are utilised.
Functional principle of the piston double diaphragm pump:
Metering pumps transfer media in two stages, the intake stroke and the output stroke. During the intake stroke liquid is pulled into the pump cavity and past the inlet valve. During the output stroke the inlet closes and the output valve opens and the fluid is
forced out.
Double Valves - GFK type
The flow may be varied by changing the motor speed or adjusting the stroke length. Typical applications can include one or more of the following, low flow rate, high accuracy, high system pressure, difficult media, corrosive, hazardous, high temperature, high viscosity or if it’s a slurry and also dosing may be controlled by computer, microprocessor, DCS, PLC or flow proportioning.
Due to the reciprocating action and two stage operation of dosing pumps the delivery is pulsating and additional equipment must be installed in order to obtain a consistent flow. Pulsation dampers fitted to the delivery of dosing pumps achieve this while also reducing pipe vibration and overall system component stress.
Installation of a Pulsation Dampner
Notebook 1 : “What is a dosing or metering pump.?”
Notebook 2 : “How do I select a dosing pump?”
Notebook 3 : “How do I install a dosing or metering pump?”
Notebook 4 : “What does a complete dosing pump installation look like?”
Notebook 5 : Continues the discussion on liquid dosing technology.
If you have any questions please go to liquiddosing@dosetech.co.za
Pumps
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