Atlas Copco GA 90 Instruction Book page 73

Instruction book
This recommendation is a general guide line for acceptable coolant quality.
Type of system
First, it is important to consider whether you are dealing with a closed system or an open system. In a closed
system, the same cooling water circulates through a system without contact with air.
An open system is a pass-through system, or a circulating system with a cooling tower. In the latter case, the
composition of the water that enters the cooler must be considered, and not the composition of the make-up
water. Due to the evaporative effect in the cooling tower, much higher concentrations of ions can be obtained
in the circulating water than in the make-up water.
Ryznar stability index (RSI)
The Ryznar Stability Index (RSI) is a parameter for predicting whether water will tend to dissolve or precipitate
calcium carbonate. The adhesion of scaling deposits and their effect are different on different materials, but
the equilibrium of the water (scaling or corrosive) is only determined by its actual pH value and by the
saturation pH value (pH
The saturation pH value is determined by the relationship between the calcium hardness, the total alkalinity,
the total solids concentration and the temperature.
The Ryznar Index is calculated as follows :
RSI = 2*pH - pH
s
Symbol
pH
pH
s
The pH is calculated by using :
s
pH = (9.3 + A + B) - (C + D)
s
Symbol
A
B
C
D
The values of A, B, C and D can be found in the following table.
Total dissolved
solids (mg/l)
50 - 300
400-1000
2920 1475 06
).
s
Explanation
Measured pH (at room temperature) of water sample
pH at saturation
Explanation
Depends on the total solids concentration (mg/l)
Depends on the highest cooling water temperature (˚C/˚F), (T=75 ˚C/167 ˚F)
Depends on the calcium hardness (ppm CaCO
-
Depends on the HCO
3
A Temperature
(˚C)
0.1 0 - 1
0.2 2 - 6
7 - 9
10 - 13
14 - 17
18 - 21
22 - 27
3
concentration or M-alkalinity (mval/l)
B Ca-hardness (ppm
CaCO )
3
2.6 10 - 11
2.5 12 - 13
2.4 14 - 17
2.3 18 - 22
2.2 23 - 27
2.1 28 - 34
2.0 35 - 43
)
C M-alkalinity (mval/l) D
0.6 0.20 - 0.22
0.7 0.24 - 0.26
0.8 0.28 - 0.34
0.9 0.36 - 0.44
1.0 0.46 - 0.54
1.1 0.56 - 0.70
1.2 0.72 - 0.88
1.0
1.1
1.2
1.3
1.4
1.5
1.6
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