Factors to Consider When Choosing a Dosing Pump

Dosing Pump are used to add a variety of chemicals into a process at accurate and controlled flow rates. They are widely used in water treatment, agriculture, factories, mining and the medical industry.

They can be directly programmable or connected to a timer to operate on a schedule. Some pumps also provide a number of features like alarms or a low tank signal.

Pump Types

Dosing pumps are used for a Dosing Pump range of applications but they are all used to pump a very precise volume of chemical or other substance into a water, steam or gas flow. They are categorized as positive displacement pumps and can be small to provide an extremely precise dose rate for maximum control.

Different pumps function in very distinct ways based on their design, size and construction. For example a diaphragm-type pulse injection pump uses an electromagnetic push-rod driven solenoid coil to dispense chemicals and operates by changing the volume of the pump head chamber with each cycle causing the diaphragm to either move up or down. The time-gap between these pulses then determines the pump head output. This type of dosing pump is a good choice for chemical dosing because of its simplicity both mechanically and electrically & relative inexpensiveness.

A gear, screw or lobe dosing pump is designed for higher viscosity liquids with shear-sensitive material such as sludge, slurry or thickened product. They use rotating gears to move a shear-sensitive material through a cylindrical chamber and are generally used for chemical dosing at relatively high temperatures.

A peristaltic pump is a very common low-cost option that can be used for a variety of fluids. It uses an elastomeric tube with a series of sealing glands that allow the dosing line to be connected to the pump. Often this is a very rigid PVC or PE tube but for steam, hot water or high pressure applications it can be stainless steel. A foot valve and a suction line are typically attached to the pump as well. Often there will be a control system installed to ensure that the pump is accurate and turning on and off at the appropriate times which can be as simple as a flow switch or timer right up to a full SCADA or similar central control system for sensors like pH, chlorine and others and integrated into larger systems.

Flow Rate

Flow rate is one of the most important factors to consider when selecting a dosing pump. This enables you to determine how much of the chemical is being dosed per minute and ensures that the correct amount of chemical is being fed into your system. Various pump models can vary in this parameter so make sure you know how much chemical you need to dose per day or hour before choosing a model.

Dosing pumps use a variety of different methods to dose chemicals into a fluid but they all involve drawing a fixed volume of the chemical into a chamber before injecting it into a pipe or tank. This can be done by using piston, diaphragm, or peristaltic action.

Pump manufacturers offer a range of specifications that can help you match the right dosing pump to your system requirements. These include a wide variety of characteristics such as flow rate, head, pressure rating, power, and operating temperature. Engineering360’s Pump Specs page is an excellent resource for learning more about these parameters.

The physical size of the pump is also an important consideration. This can influence where you mount it within your system to prevent the pump from causing obstructions or siphoning problems. Dosing pumps are usually relatively small in comparison to other industrial pump types but they still need to be able to handle the specific media being pumped, which can be very corrosive or dangerous.

Dose Rate

A dose rate is a very important factor to consider when it comes to radiation exposure. It has been demonstrated that molecular, cellular and tissue outcomes change significantly as the dose rate increases. This is because cells have different protective mechanisms that are effective at varying rates of exposure. This has been referred to as the AOP/key event approach and is similar to the approach used for chemicals (Edwards et al, 2016).

For example, lung fibroblasts have a cell turnover time of 30 days whereas bone marrow stromal cells have a cell turnover of two days. When the same dose of radiation is given to a lung fibroblast and a bone marrow stromal cell at identical exposure times the frequency of chromosome aberrations is far greater for the stromal cell than the lung fibroblast. This is because the cellular defences are less effective at higher dose rates (Feinendegen et al, 2007).

This is why it is critical that the dosing pump be placed in the correct location in the pipe stream. It needs to be close enough to a water source so that it can be activated, but not too close as this could cause problems further up the pipe. It also needs to be situated where it will not effect other pipe parts such as a valve or water meter that may get prematurely corroded, not read properly or have build up of scale or sludge.

Control

Regardless of the type of dosing pump, all models come with a control system that turns it on and off and manages the flow. This can be in the form of an electrical or air actuator depending on the model and application.

In most cases the dosing pump will need to be connected to a power source, compressed air and be located in a suitable position. Ideally, it will be located next to or below the dosing point to prevent siphoning and close to the water or chemical source. This is important as it ensures that the product is added to the water or chemical Dosing Pump at a constant rate and will not affect any other pipe parts such as a valve, water meter etc.

The SMART Digital S DDA and SMART Digital XL DDE Grundfos dosing pumps are an example of this and come with pulse control, a simple external stop function, and a dosing alarm (e.g. empty tank signal).

Ultimately, the control system is what will make or break a dosing pump. Depending on the application and requirements, the control system will vary in complexity. However, the dosing pump should not require a lot of input from the operator once it is correctly set up. Ideally, it will also be able to sense when the product needs topping up and alert the operator or shut down to avoid any untreated water or product traveling back up the pipe causing issues later.