CENWAT Inhibitor & Water Treatment 4

Question 1

What is a polyphosphate scale inhibitor dosing unit?

Accepted Answer

A device that slowly releases food-grade polyphosphate crystals into the water supply to inhibit scale and corrosion on heat exchanger surfaces

Answer

A polyphosphate dosing unit releases small amounts of polyphosphate into the water stream, sequestering calcium and magnesium ions to inhibit scale formation on boiler and heater surfaces in hard water areas.

Question 2

What is an electrolytic scale reducer?

Accepted Answer

A device using a zinc or titanium alloy rod to alter the crystal structure of calcium carbonate, reducing adhesion to surfaces

Answer

An electrolytic scale reducer uses dissimilar metals to create a small galvanic current that changes the crystalline form of calcium carbonate from adherent calcite to non-adherent aragonite, reducing scale deposits.

Question 3

What effect does limescale have on the efficiency of a boiler heat exchanger?

Accepted Answer

It acts as an insulating layer reducing heat transfer, increasing gas consumption and potentially causing overheating and premature failure

Answer

Even a thin layer of limescale (1 mm) significantly reduces heat transfer efficiency (by approximately 7–10%), increasing fuel consumption and potentially causing the heat exchanger to overheat.

Question 4

What is the recommended approach for water treatment when replacing a boiler in an existing, heavily sludged system?

Accepted Answer

Power flush the existing system with a system cleaner before installing the new boiler, then dose with inhibitor

Answer

Installing a new boiler into an untreated sludged system will rapidly contaminate the new heat exchanger; the existing system must be power flushed and treated with inhibitor before the new boiler is connected.

Question 5

What information should be recorded about water treatment on the boiler's Benchmark logbook?

Accepted Answer

The type and dose of inhibitor used, the system volume, water hardness, whether a scale inhibitor was fitted, and date of treatment

Answer

The Benchmark commissioning checklist requires the engineer to record water hardness, the inhibitor product and dose, system volume treated, and whether a scale inhibitor or softener was fitted.

ACS CENWAT Practice Test

ACS CENWAT Practice Test

CENWAT Inhibitor & Water Treatment 4