Atlas Copco ZR-55, Instruction Book

Page: 91 / 138

Ref Name
(15) To be installed by the customer
4.5 Cooling water requirements
Recommendations
The cooling water quality must meet certain minimum requirements.
No general recommendation can encompass the effects of all combinations of the various compounds, solids
and gases typically found in cooling water in interaction with different materials.
Only non-treated water must be used.
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
s
).
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
s
- pH
Symbol Explanation
pH Measured pH (at room temperature) of water sample
pH
s
pH at saturation
The pH
s
is calculated by using :
pH
s
= (9.3 + A + B) - (C + D)
Instruction book
9 0