2-12.1 ESTABLISHED SOLUTION STRENGTH, RANGE CONTROL, AND PUMP SETTING.
a. The first step is to estimate the flow rate to be expected, based on pumping capacity, filter flow, etc. This
need only be an approximate figure to determine if flow is to be less than 10, or over 100 GPM at the start,
but is it important to know if flow can be expected to increase or decrease considerably from the starting
b. Establish a tentative dosage to produce the residual desired. This is a function of chlorine demand, or
the amount of contaminants in the water. Again, this need not be exact, as dosage and solution can be
increased more conveniently and reliably than it can reduced, it is customary to start with a PPM dosage
for a 1 PPM residual and by means of residual test make the necessary final adjustment.
c. Curves have been prepared to assist in this process. For example, suppose it is known the water pump has
capacity of 70 GPM. This is in the intermediate range of the system. Use 1 PPM as the tentative dosage and
refer to Figure 21 of manual overpacked with equipment. At 70 GPM and 1 PPM a daily feed rate of about
20 ounces of 70% calcium hypochlorite will be required.
d. The mid-range capacity of the hypochlorinator is 2-1/3 GPH and in the lower section of Figure 21 the
required amount of chemical would be fed at this capcity by making up a 0.175% solution. One and three-
quarter ounces of calcium hypochlorite in five gallons of water will give this concentration.
e. Best procedure for establishing range control setting is to consider whether the nominal 60 GPM will be a
maximum or not. Usually transfer of water by pump from detention to storage gives increasing total
dynamic head on the pump as the supply level falls and discharge level rises. This means the maximum
flow at the start, unless the system has multiple pumps and/or storage system. If the starting rate is
known to be maximum, the range control valve is gradually closed until the pump is making 24 strokes per
minute, or register shows 14 gallons flow in one minute. The system will now correct itself automatically as
it slows down.
f. Following this procedure, the pump is set at approximately 50% stroke and the results of the residual test
are used to increase or decrease dosage as required. Once the correct residual is reached, the treatment
will vary automatically in proportion to flow over approximately, 10:1 range without further adjustment of
the pump or the range control valve.
g. Supposing chlorine demand is abnormally heavy and the desired residual is not found at maximum stroke.
For example, at 50% setting there might be only 0.2 residual. An increase in solution strength is indicated
to increase dosage by 0.8 PPM. If flow range and pump are correct, they should not be changed and the
range control valve is left alone. In the example given to get 0.8 PPM more at 70 GPM would require about
sixteen more ounces of 70% calcium hypochlorite per day which corresponds to an increase in solution
strength of 0.15% for a 2-1/3 GPH rate. To increase by this amount, 1.5 ounces of dry chemical would be
added per 5 gallons of original solution. This should restore the correct residual at close to the 50% nominal
h. Most reliable operation of the equipment calls for midcapacity stroke length settings and stroking rates.
This keeps the pump primed, minimizes effects of sediment and impurities in the solution, and gives
maximum mixing and distributions of active chlorine in the water system.
i. Under normal conditions, it will be necessary to make up fresh solution about every two hours. Mixing of
dilute solutions is easier than for highly concentrated solutions and less precipitation of impurities from
hard water will occur. It is recommended that 60 gallons of solution be made up at a time.