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About Metering Pumps
Metering pumps, also referred to as dispensing, liquid,
chemical feed, proportioning and fluid metering pumps, are positive displacement
pumps that move exact amounts of liquid in any given time frame, resulting
in accurate flow rates. These pumps move a consistent volume of liquid
with each cycle or revolution. The distinguishing characteristic of these
pumps is their accuracy. Metering pumps have an average accuracy rate
of plus or minus one percent. Another feature of metering pumps is their
ability to vary the flow rate. This is either manual or automatic, depending
on the system and process requirements.
Metering pump manufacturers equip the majority of their products with
a micrometer screw adjustment, but a pneumatic or electronic actuator
can also be used if the pump flow rate requires alteration due to a process
signal. These pumps move fluid in two stages. First is the intake stroke
in which liquid is carried into the pump cavity beyond the inlet check
valve. In the next stage, after the inlet valve closes, the outlet valve
opens and the fluid is forced out. Altering the stroke length or stroking
speed adjusts the flow rate of the metering pump.
Metering pumps can be dispensing devices of chemicals and other fluids.
Typically, these pumps are used to meet any or all of the following requirements:
high accuracy dispensing, high system pressure, low flow rates in GPH
or mL/hr, the ability to move hazardous or corrosive fluids or controlled
dispensing via a microprocessor, computer or PLC. Water treatment systems,
chemical processing and laboratory applications utilize metering pump
manufacturers. Plastic
extrusion machines use metering pumps to maintain
a constant flow of melted plastic through the die. These pumps are also
great for spray paint applications, as they enable quick changeover of
colors. Additionally, manufacturers of processed food use metering pumps
to ensure a constant rate of food additives during their processes.
Different factors determine which metering pump is appropriate for a
specific application. Since each fluid that needs to be pumped is unique,
it is important to select a pump based on the specific characteristics
of the fluid, such as whether or not it is abrasive or corrosive. Some
other important factors include fluid viscosity, temperature, flow and
pressure rates. Since metering refers to the accurate delivery of a measured
amount of liquid, metering pump manufacturers cater to numerous applications
throughout the world.
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Types of Metering Pumps
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transport fluid via a reciprocating bellows cavity that joins to a driving
rod.
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use a revolving disk attached to a drive shaft that transports fluid
without pulsation as it spins.
- are precise instruments used to move chemicals.
- are designed to dispense a precise amount of liquid or gas.
- use
gears to trap fluid between the teeth of two or three rotating gears.
Gear pumps are ideal for high system pressure applications and are typically
magnetically powered.
- use displacement to move fluids from one place to another.
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use tubing in their operation and rollers that squeeze or occlude the
tubing in the direction of the flow. First, the rotor rollers apply
pressure to the tubing, which pushes the fluid in, and then the tubing
returns to its shape following the occlusion, which creates a vacuum
that pulls more fluid in.
- transfer liquids and gases from an area of high pressure to an area of low pressure.
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use a reciprocating plunger to displace liquid through the machine.
A rigid piston assembly gives them the maximum pressure and accuracy
of metering pumps.
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