Chemical injection pumps (also known as dosing or metering pumps) are used to insert or pump chemicals into pipelines, liquid streams, storage tanks or in industries such as agriculture, oil/gas, water/wastewater treatment, etc. They have many functions, including antifreeze, corrosion inhibition, friction reduction, pipe fouling inhibition, product reaction catalysts, chemical migration in applications such as: fertilizers, herbicides, pesticides, fungicides, nematicides and transport through irrigation systems growth regulator. Typically, chemical injection pumps are driven by AC or DC motors, and in DC motor applications, chemical injection pumps typically use DC permanent magnet motors. Brushless DC motors are also used in applications requiring high power efficiency and advanced functionality, such as chemical reagent flow metering.
Chemical Jet Pump System
A chemical injection pump system usually consists of a pump, gate valve, check valve, prime mover (motor), storage tank, filter, directional valve and interlock. They accurately pump controlled volumes of liquid from a storage tank to a system receiving chemical additives using reciprocating positive displacement pumps driven by variable speed DC motors that ensure proper speed based on travel speed.
The types of positive displacement pumps used in chemical injection pump systems are diaphragm pumps and plunger pumps. Diaphragm pumps pump chemicals through an electromagnetic solenoid, which is connected to the diaphragm of the pump, and when the solenoid is energized by a control circuit , it moves the diaphragm, which in turn expel the chemical additive fluid under pressure from the pump outlet. When the solenoid is de-energized, the diaphragm returns to its original position and draws more chemical fluid into the pump's inlet, and the cycle repeats when the solenoid is energized and de-energized. Plunger pumps use reciprocating, single- or double-acting cylinders to draw chemical fluid into the pump and discharge it from the pump's discharge end. They are used in metering applications to provide a predetermined liquid flow.
Use of DC Motors in Chemical Injection Pumps
DC motors act as prime movers for chemical injection pumps, motors are more cost-effective than engine-driven prime movers, and they are less expensive to install and maintain. Plus, the electric motor incurs no external costs related to fuel or emissions compliance. Some chemical injection pump systems are solar powered, which extends another cost saving advantage. Solar power systems use solar cells to generate electrical current through the photovoltaic effect, which is connected to a battery pack, which in turn powers a DC motor to drive a pump.
Two types of motors are commonly used in chemical injection pump motors: DC permanent magnet motors and brushless DC motors, DC permanent magnet motors have sealed bearings and heavy duty brushes, which offer the advantages of low current/power consumption, high reliability and low maintenance . Brushless DC motors are used in applications requiring continuous duty, variable speed and high torque response to maintain a constant pump speed even with pressure changes. Brushless DC motors using digital controllers provide chemical injection pumps with the added benefit of improving the precision and accuracy of injection rates, preventing over-injection, and correspondingly reducing reject rates.
