A reliable dosing specification converts a treatment objective into hydraulic, chemical, material and control requirements that suppliers can interpret consistently. Without that foundation, one bidder may size for average consumption, another for maximum flow, and a third may assume atmospheric discharge. The quotations look comparable only because the missing assumptions are hidden.
Jams (Pvt.) Ltd recommends building the specification in layers: define the water duty, calculate the chemical feed range, establish pressure and suction conditions, select compatible materials, describe controls and list the accessories and documents required. This method applies to process water, cooling or boiler make-up, pretreatment and many other industrial water-treatment duties.
1. State the treatment objective and battery limits
Begin with a short process statement. Identify the source water, treated-water destination, reason for dosing and the boundary of supply. Examples include pH adjustment before clarification, antiscalant before a membrane, disinfectant into a storage line or corrosion inhibitor in a make-up stream. Avoid naming a pump before the process need is clear.
Define whether the package includes only the metering pump or also a day tank, mixer, calibration column, valves, instruments, panel, skid piping, injection assembly and commissioning. State which party supplies external cabling, civil base, bulk chemical transfer, bunding and connection to the plant control system.
2. Record the water flow envelope
Provide minimum, normal and maximum water flow, not a single design number. Add operating hours, batch size where relevant and the expected rate of change. A make-up line that runs steadily requires a different control and turndown approach from a batch fill that starts and stops several times each hour.
Include water pressure and temperature at the injection point, pipe material and size, and whether the line can drain or remain pressurized after shutdown. If process flow is measured, identify the meter output, scaling and update behaviour available to the dosing system.
3. Convert treatment dose into chemical feed
State the target dose and basis clearly—for example, mass of active chemical per volume of water. Then identify the commercial product strength, prepared solution concentration and density used in the calculation. This distinction matters: a target stated as active material cannot be entered directly as litres per hour of diluted solution.
A simplified design sequence is:
- multiply water flow by the target active dose to obtain required active mass per unit time;
- divide by the active fraction of the prepared dosing solution;
- convert mass flow to volumetric feed using solution density; and
- repeat for minimum, normal and maximum water flow and dose conditions.
Use consistent units and have the calculation independently checked. Add a reasonable design margin based on known uncertainty and future duty, but avoid gross oversizing. A pump operated near the bottom of its controllable range may produce less stable dosing than a correctly sized unit.
4. Establish real discharge pressure
The pump must overcome pressure at the injection point plus relevant line and accessory losses. Record normal and maximum process pressure, elevation effects and any back-pressure device. For long small-bore dosing lines or viscous liquids, friction may be significant. A statement such as “pump pressure 10 bar” should be a derived requirement, not an arbitrary round number.
Also assess the opposite condition. If the chemical tank sits above a low-pressure injection point, gravity or siphoning can cause uncontrolled feed when the pump stops. Injection and back-pressure arrangements should be selected for the actual hydraulic layout.
5. Describe suction conditions honestly
Provide tank level relative to the pump, suction-line length and diameter, number of fittings, fluid temperature, viscosity and gas-release tendency. Note whether the chemical can crystallize, settle or contain solids. Flooded suction is often helpful, but it does not remove every priming or gas-handling issue.
Locate the pump for safe access and short, simple suction piping where practical. A distant pump connected by a long narrow tube may fail to deliver its expected rate even though the discharge-side calculation is correct.
6. Verify materials and containment
List the chemical name, supplier and all intended concentrations, including cleaning or flushing fluids. Specify ambient temperature and exposure to sunlight or washdown. Wetted materials include more than the pump head: valves, diaphragm or plunger seal, O-rings, tubing, injection fittings and instruments must all be considered.
Compatibility references provide initial guidance, but unusual or severe duty may require confirmation from the chemical and equipment manufacturers. Define leak containment, drain destination and relief return. The specification should never route hazardous discharge vaguely “to floor drain.”
7. Write the control narrative
State whether operation is manual, fixed-rate, pulse-paced, analogue flow-proportional, batch-controlled or closed-loop. List start permissives, tank low-level action, process-flow loss, remote stop, pump alarm, standby changeover and local/remote selection. Define signal types and scaling rather than saying only “PLC compatible.”
For feedback control, identify the measured variable, sensor location, sample delay and acceptable response. The pump’s maximum capacity and control range must accommodate the process without driving the loop into continuous saturation.
8. Specify maintainability and acceptance
Provide isolation, depressurization and calibration facilities that allow technicians to work safely. Identify expected consumables and critical spares. Ask bidders to state capacity at the specified pressure, materials, power, control features, included accessories and deviations in a common schedule. The JAMS metering-pump service area can be a starting point for discussing available approaches.
Define commissioning and acceptance separately. Installation checks, signal tests and operator handover are not automatically a formal capacity or process-performance test. If measured feed accuracy is an acceptance criterion, state the method, test liquid, pressure, duration, tolerance and responsible party.
A concise enquiry package
A strong request for quotation includes the process description, completed duty sheet, chemical safety data, piping sketch, control narrative, scope boundary, document list and requested site services. It also identifies unknowns. An explicit “maximum pressure to be confirmed” is safer than a guessed value hidden in the specification.
JAMS can review this information and help develop a suitable selection without claiming that one pump fits every water-treatment task. Final process performance depends on the water chemistry, treatment design, installation and operation as well as the metering equipment.
Frequently asked questions
How much spare capacity should a dosing pump have?
There is no universal percentage. Margin should reflect calculation uncertainty, chemical-strength variation, expected future duty and the consequence of reaching maximum output. Too little margin limits operation; too much can place normal demand below the pump’s useful control range. Evaluate both ends.
Should duty be specified in litres per hour or kilograms per hour?
Use the unit that keeps the treatment calculation clear, and provide enough information to convert. Active dose is often mass-based, while pump capacity is commonly volumetric. State concentration and density at the relevant temperature so the conversion is traceable.
Is a back-pressure valve always required?
No. It is selected when the hydraulic conditions or pump arrangement require controlled back pressure, anti-siphon behaviour or improved valve operation. It also adds pressure loss. Review the complete suction and discharge system rather than adding one by default.
What information is most often missing from dosing enquiries?
Maximum injection pressure, minimum required feed, prepared chemical concentration, density, suction arrangement, material constraints and control-signal details are frequent gaps. A piping sketch and chemical safety data often reveal issues that a simple flow-and-pressure request misses.
