A dosing pump is a small, positive displacement pump. It is designed to pump a very precise flow rate of a chemical or substance into either a water, steam or gas flow. A dosing pump will deliver this precise flow rate of chemical or other product by a number of different methods but it generally involves drawing a measured amount into a chamber and then injecting this volume of chemical into the pipe or tank being dosed. Dosing pumps are used in a variety of applications from agriculture, industry, manufacturing to medicine.
Major Parts of Dosing Pump
- The chemical tank or container: The product that is being dosed.
- The foot valve: This is a one way valve that is attached to a suction line.
- The pump itself: This can vary in size and materials but is generally a variety of chemical resistant plastic (PVC, PE or similar), rubbers or stainless steel. It has a suction line attached to the inlet and the dosing line attached to the suction. The mechanics of the pump can vary.
- The dosing line this is generally a fairly rigid PVC or PE tube or a reinforced hose.
- The injector: At the point at which the product is injected into the product, there is an injector point. This is a one way valve so that when the dosing pump pushes an amount of product into the line it can overcome the pressure in the delivery pipe and allow the product out into the flow.
- Control system: A control system is installed to ensure the dosing pump is accurate and turns on and off at particular times.
Types of Pumps:
There are 4 different types of dosing pumps, they vary in their action and pumping mechanism and are suited to various different applications, pressures and chemicals
- Diaphragm type constant injection: Where there is a pump chamber that is filled and emptied by a piston and diaphragm and valves on the inlet and outlet. When the chamber is filled by drawing in the piston, then depending on the amount being dosed the dosed volume is injected out at a certain speed. These pumps are very accurate and deliver a near constant flow rate of product. With correct control, they can also deliver variable dosing rates
- Diaphragm type pulse injection: This is where there is a diaphragm mechanism again but instead of a slow and constant flow rate, the pump is controlled by a solenoid coil. This coil sucks in and injects the chemical pulses with the time gap between pulses providing the control of flow rate. This makes this type of pump much less accurate as the product is delivered in pulses with a time gap between injections. They are generally very simple both mechanically and electrically and are also very cheap.
- Lobe type pumps: This type of pumps allows a certain volume through a set of meshing gear type impellors. The volume in between these impellers is possibly not as accurate as the proper diaphragm pumps and they also have a wearing surface so they are only really suitable when the product is of high viscosity and self-lubricating so wear is minimized.
- Peristaltic pumps: Peristaltic or lobe pumps are a specialized and very accurate method of dosing. The mechanism works by having a flexible tube which the product has to pass through. This tube is bent in a semi-circle and a small roller on a mechanical arm moves over the outside of the tube. This action captures a “portion “ of the product in the tube and pushes it along and into the dosing tube and the main stream.
- Water treatment
- Medical and Food Processing