25 May 2005
from pumps directly connected to base tanks. The base tanks are refilled by the water
treatment supplier, thereby eliminating the handing of products by the user. The
product is fed directly from pumps into the cooling or boiler water system.
Figure 7-4. Automatic Neat Chemical Feed
CHEMICAL CONTROL VERIFICATION. To ensure that systems are
being maintained within water treatment program control limits, it is necessary to verify
that the proper water treatment chemical dosages are being used in treated water
systems. Verification involves one or more of the various methods described below.
Continuous Testing. Continuous water testing can be used in large
systems where the service requirement justifies continuous control or the cost of the
chemical feed warrants close control. This technique requires monitoring devices that
are external to the system, which is equipped with probes and transmitters that send
signals to the monitoring device. These systems are often linked directly to the chemical
feed system to provide automatic control of the chemical feed.
Manual Testing. Manual testing of the levels and dosages of water
treatment chemicals is the most common method of testing. This technique is effective
in systems in which the treatment chemical levels are not expected to vary widely in
short periods of time, or in which the treatment chemical feed can be linked to the
makeup water flow rate. Normally, the results of the manual testing are used to
manually adjust the chemical feed rates. The testing frequency varies depending on the
type and size of the water system. Critical systems require the most attention.
Little or No Testing. Testing is necessary except in instances in which a
chemical feed system does not require daily control monitoring or in which there is no
treatment. This technique is used, for example, at remote cooling towers where a slowly
soluble chemical is suspended in the cold well. Even for such systems an occasional
test for treatment chemical level is recommended.