Choosing the right metering pumps for water treatment

Metering pumps are used in an assortment of municipal drinking water as well as wastewater applications. They are suitable for applications which require dispensation of treatment chemicals for disinfection, filtration and clarification.

This is because the pumps are able to alter the amount of chemical dosage rates according to the process conditions.

With all things considered, metering pumps are undoubtedly one of the most multipurpose technologies chemicals in municipal water applications. Nevertheless, there are variables that need be evaluated during the choosing and installation of the proper metering pump or complete chemical-feed system. As such, proper pump and feed system selection will help inject liquids or slurries regardless of viscosity. This is in addition to ensuring efficiency.

Sizing
Size is one of the most important factors that matter when determining the proper metering pump to be used. This is especially the case when it comes to capacity of both the pump’s flow rate and discharge pressure.

This is because a metering pump should be sized so that its maximum expected flow rate is 85% to 90% of the pump’s capacity. Leaving behind additional capacity is thus ideal. This also applies the other way round in the pump’s minimum capacity.

Metering pumps are selected based on the proper flow rates, discharge pressures and type of fluids to be pumped in the specific application. Once this is accomplished, one can now move to selective the type of metering pump. These vary from diaphragm, mechanically actuated diaphragm, solenoid driven or piston style.

Materials of Construction
The selection of a metering pump must take into consideration any corrosion, erosion or solvent action that may occur when handling specific substances. For example, solvents may dissolve pump heads constructed of plastic, acids and caustics may only be compatible with stainless steel or certain steel alloys, and abrasive slurries can erode some materials.

Also Read: 4 factors to consider when selecting the best chemical metering pump

As such, the best lines of metering pumps will be available in a range of materials of construction. These allow the end-user to choose the appropriate option for his specific application.

Drivers
A meter pump driver should be chosen by matching it to utilities such as electric, air, gas or other means of driving the pump. You should also take into account the environment in which the pump will operate, so as to prepare for hazardous-areas.

Control Systems
Control systems usually include manual continuous operation, on/off operation or automatic proportional control in response to a process signal. Generally, metering pump flow rates can be manually adjusted through the use of a micrometer dial that allows the pump to be operated between 10% and 100% of capacity.

Metering pump flow rates can also be controlled automatically by electric positioners that change the pump’s stroke length. This is also achievable through the use of variable speed drives that alter the stroking speed.

That being said, it is impractical to use a variable speed drive on motor-driven pumps that normally operate at less than 100 spm. This is because slowing the motor causes each stroke to take longer from start to finish. Furthermore, hydraulic motor-driven pumps should not be operated at less than 15 spm.

The metering pump application as well as level of quality should also be considered. The selected metering-pumping technology should offer the best in operation, reliability and energy efficiency when handling a wide array of liquids, chemicals and slurries.