A cooling tower concentrates everything that enters its circulating water. Evaporation removes relatively pure water, while dissolved salts, suspended matter, treatment chemicals, and biological nutrients remain behind. That is why a tower that appears mechanically healthy can still develop scale, corrosion, slime, and heat-transfer loss. Chemical treatment must respond to circulation, make-up quality, blowdown, temperature, metallurgy, and operating schedule; it cannot be sized responsibly from basin volume alone.
From an applications engineering perspective at Jams (Pvt.) Ltd, inhibitor and biocide feeds are two different duties sharing the same system. Inhibitor is commonly maintained as a continuous or flow-related concentration. Oxidising and non-oxidising biocides may be fed continuously, intermittently, or as a controlled slug according to the treatment programme. Our water treatment and disinfection service treats these requirements as a complete operating strategy rather than as isolated pump capacities.
What the dosing programme is trying to control
Corrosion inhibitors reduce attack on carbon steel, copper alloys, and other wetted metals when chemistry remains within the intended range. Scale inhibitors help keep hardness salts from depositing on condenser tubes, fills, and heat exchangers. Dispersants assist with suspended solids. Biocides control organisms that can form biofilm, restrict airflow or water distribution, create under-deposit corrosion conditions, and interfere with process hygiene.
These chemicals do not remove the need for blowdown and physical maintenance. Cycles of concentration are limited by the make-up water and system design. Conductivity control is often used as a practical indicator for bleed, but conductivity does not identify every individual ion or confirm microbiological control. A sound programme links chemical feed, blowdown, monitoring, and inspection.
- Make-up analysis establishes hardness, alkalinity, chloride, silica, conductivity, and other relevant limits.
- Heat load and evaporation determine how quickly dissolved material concentrates.
- Blowdown and drift remove water and treatment chemical from the circuit.
- System metallurgy and process contamination affect corrosion and biocide choices.
- Operating hours, seasonal loading, and idle periods change the required dosing schedule.
Start sizing with a water and chemical balance
For continuous inhibitor feed, the most useful starting point is usually make-up flow and target product dosage. If make-up varies, size from its credible range and consider a flow-paced command. Product feed in litres per hour follows from make-up flow, desired product concentration, and product density. The selected pump should handle maximum demand while remaining controllable during normal and minimum operation.
A second method checks treatment loss through blowdown and other water losses. At steady operation, the chemical entering should balance the chemical leaving or being consumed. The two calculations should broadly agree when the assumptions are consistent. If they do not, investigate unmeasured overflow, leaks, process contamination, changing cycles, or an incorrect concentration basis. This reconciliation is more valuable than adding an unexplained safety factor.
Biocide feed is a time-based duty
A slug dose is defined by total product volume and the time allowed to inject it. A basin requiring a given treatment volume over one hour needs a very different pump from the same volume spread over eight hours. The calculation must also account for the actual system volume, not just the tower basin. Headers, exchangers, remote pipework, and process equipment can hold a substantial portion of the circulating inventory.
The dosing window should suit circulation and contact time. Blowdown may need to be coordinated with a biocide event according to the approved treatment procedure, but it should never be disabled without suitable safeguards and operating review. Oxidising biocide control may use ORP or residual measurement where the chemistry supports it; a timer alone cannot show whether demand has changed.
Selecting pumps and the injection arrangement
The pump must meet flow at the real discharge pressure. Tower feeds are often low pressure, which creates its own challenges: siphoning, inconsistent check-valve seating, and sensitivity to changing injection conditions. A back-pressure or anti-siphon valve may be necessary. The injection point needs turbulent mixing and should be far enough upstream of the monitored location to provide a representative response.
Different chemicals should normally have dedicated pumps, suction assemblies, injection valves, and clearly identified tubing. Combining lines can produce reactions, precipitation, gas, or loss of treatment effectiveness. The JAMS metering-pump service considers liquid-end material, valve design, control input, enclosure, and accessories together. Chemical compatibility must be checked at the supplied concentration and expected temperature, not inferred from a broad product name.
Capacity and turndown
Normal inhibitor demand should not sit at the extreme bottom of an oversized pump’s range. For intermittent biocide, however, enough capacity is needed to deliver the calculated slug within the allowed window. If one proposed model cannot serve both conditions well, separate pumps are the proper solution. Duty/standby philosophy should also reflect consequence: a critical continuously operated cooling circuit may justify installed redundancy and automatic alarm transfer.
Control and interlocks
An inhibitor pump can be paced from make-up water flow because chemical leaves the system largely with water losses. It should stop on low chemical level and loss of relevant process permissives. A biocide pump may be enabled by schedule, circulation proof, and operator authorisation, with a maximum run-time limit. Conductivity bleed control, inhibitor feed, and biocide sequencing should be documented so that one loop does not unknowingly defeat another.
Commissioning checks that matter
Before chemical is introduced, verify wiring, rotation where applicable, valve orientation, relief route, tank level input, and the control response. Prime with a safe procedure suited to the chemical. Then measure delivered volume using a calibrated column or another approved method at representative pressure. Record the pump setting, command signal, measured flow, solution concentration, and date. This baseline gives operators something concrete to compare after maintenance.
Sampling deserves the same discipline. A sample taken next to the injection quill may show a reassuring concentration that is not representative of the circuit. Dead legs can hide microbiological growth. Conductivity probes foul, corrosion coupons require correct exposure and interpretation, and microbiological tests have handling limits. Chemical feed should be adjusted from a coherent set of observations, not one convenient reading.
Common pitfalls in tower dosing
- Sizing from basin volume while ignoring the rest of the circulating system.
- Using average make-up flow when peak daytime evaporation controls maximum inhibitor demand.
- Feeding incompatible products through a shared line or adjacent injection points without review.
- Allowing a low-pressure discharge to siphon after the pump stops.
- Treating conductivity as direct proof of inhibitor residual or biological control.
- Leaving idle towers full and untreated without a shutdown and restart procedure.
Another frequent issue is changing product concentration without recalculating pump settings. A litres-per-hour setting is not a dose until product strength and water flow are known. Similarly, copying a programme from another tower ignores differences in make-up water, metallurgy, heat load, and contamination. Chemical suppliers should establish treatment targets, while the dosing equipment must be engineered to deliver those targets reliably.
When to call JAMS
Contact JAMS when a new tower is being commissioned, treatment products are changing, the pump cannot cover both seasonal extremes, or residuals vary despite repeated adjustment. Send the circulating and make-up flow data, estimated system volume, water analysis, target product dosages, product safety data, operating pressure, injection layout, control philosophy, and available electrical signals. If some values are unknown, we can identify what should be measured before equipment is selected.
We support textile, cement, chemical, and utility teams in translating a treatment programme into a practical dosing package. The objective is not to claim a universal chemistry recipe; it is to provide equipment and controls that can execute the approved programme. For application review and local support in Pakistan, use the JAMS contact page.
FAQ
Should inhibitor dosing follow circulation flow or make-up flow?
Make-up flow is often the better pacing variable because treatment chemical is lost with blowdown, drift, and other water losses that drive make-up. Circulation flow is much larger and may remain nearly constant while evaporation changes. The final choice should follow the treatment mass balance and available measurements.
How is a biocide dosing pump capacity calculated?
Determine the approved product dose, actual circulating-system volume, product concentration and density, then divide the resulting product volume by the permitted injection time. Check that the pump delivers this rate at operating pressure and still provides a controllable setting, not merely a catalogue maximum.
Can inhibitor and biocide use the same metering pump?
Generally, dedicated pumps are safer and easier to control because the chemicals have different schedules, compatibility requirements, and injection locations. Sharing also creates contamination and sequencing risks. Any common equipment would require a specific process and cleaning review, not an informal changeover.
Why does the measured residual vary even when the pump setting is fixed?
Possible causes include changing make-up flow, product strength, blowdown, process contamination, poor mixing, an unrepresentative sample, pump loss of prime, or fouled analytical equipment. Check delivery and process conditions systematically before increasing the setting, because extra chemical may conceal rather than solve the underlying fault.
