A dosing pump has one job: put a precise amount of chemical into a process. When it is chosen well, you get stable water quality and low chemical cost. When it is chosen badly, you get over-dosing, under-dosing or constant maintenance. These are the points to settle before you select a model.
1. Define the duty
- Flow range. Know the minimum and maximum dose rate. A pump works best in the middle of its range, so do not pick one that spends its life at 5 percent of capacity.
- Back pressure. Include the pressure of the line you inject into, plus friction losses.
- Accuracy. Water treatment may accept a looser tolerance than a process that feeds a reaction. Metering pumps are generally specified with repeatability in the order of plus or minus 1 to 2 percent, but check the data for the specific model.
- Fluid. Chemical, concentration, temperature and viscosity. Gas-forming liquids such as sodium hypochlorite need special attention.
2. Choose the pump type
- Solenoid-driven pumps suit small flows and simple dosing, such as small water treatment or cooling tower systems.
- Motor-driven diaphragm pumps handle larger flows and higher pressures with better accuracy and longer service life.
- Piston pumps give high pressure and accuracy for clean fluids.
- Gear metering pumps suit continuous dosing of viscous or lubricating fluids, including magnetic-drive versions with no shaft seal.
3. Pick compatible materials
Check the pump head, valves, diaphragm and seals against the exact chemical. PVDF, PTFE, stainless steel, PVC and polypropylene each suit different products. A wrong elastomer is one of the most common causes of early failure.
4. Plan the installation
- Fit a back-pressure valve if the injection point is at low pressure, to avoid siphoning.
- Use a pulsation damper for a smoother flow and to protect the line.
- Add a pressure relief valve on the discharge side.
- Keep suction lines short with a foot valve or strainer to protect the pump.
5. Think about control
You can run a pump manually, from a pulse signal, or from a 4-20 mA signal linked to a flow meter or analyser. Proportional control that follows the process flow keeps the dose steady when demand changes.
6. Standards and approvals
For oil and gas or petrochemical duty, clients often ask for controlled-volume pumps built to API 675, and for hazardous areas, certified electrical equipment. Raise this at enquiry stage, because it changes the pump and the price.
Common mistakes
- Sizing for peak demand only and running far below range.
- Ignoring the chemical concentration when checking materials.
- Leaving out a back-pressure valve and getting free flow into a low-pressure line.
- No spare diaphragms or valve kits on site.
Power Energy Gulf supplies chemical metering and dosing pumps for industrial and water treatment duties across the Gulf. See our chemical dosing pumps page, or contact us with your fluid, flow and pressure and we will suggest a suitable pump.