A chemical has several characteristics. Characteristics include physical characteristics and chemical characteristics. Some of the properties of the chemical will affect the pump selection. We shall take a look at the key factors that should be considered when making the pump selection.
Before we can look up the properties of a chemical, we need the following pieces of information:
- Chemical name, such as Hydrochloric Acid
- The concentration of the chemical, for example, 32%
- The temperature of the chemical
Physical Properties
Physical characteristics are properties that can be observed or measured, some properties include color, hardness, solubility, heat conductivity, electrical conductivity, density, melting point, boiling point, viscosity, etc.
For pump selection, the primary physical properties that must be considered are density and viscosity.
- Density. Density is the weight of a substance per unit volume, for example, pure water has a density of
0.998 g/cm3. Chemicals with higher density will take more energy to move. Therefore, higher density
chemicals will have a heavier load at the same duty point. However, when we are selecting a pump, we do
not
use density directly. We use Specific Gravity (S.G.), which is the relative density of the chemical
compared
to water. The practical reason why we use S.G. is that pump performance curves are tested using water.
We
can calculate the loading of the pump by multiplying the S.G. of the chemical.
- Viscosity. The viscosity of the chemical can be roughly described as the stickiness of the chemical. High viscosity chemicals cling to the piping walls causing more drag. It also takes more energy to move a viscous liquid. Besides affecting the loading of the pump, high viscosity chemicals will also reduce the pump performance.
Secondary properties that should be considered include melting point, boiling point, and hardness. These properties matter depending on operating conditions, which is covered in Part 3.
One last physical property that is important in special circumstances is electrical conductivity. If the chemical has very low electrical conductivity, then there is a risk of static electricity building up within the pump. Special pump material selection must be made to prevent the electricity buildup from damaging the system.
Chemical Properties
Chemical properties are changes from reaction or interaction. Chemical properties include corrosiveness, acidity (pH), flammability, etc. For chemical pumps, the pH of the chemical does not tell us the corrosiveness nor what material is suitable for the chemical. While corrosiveness can be an indication, e.g. the concentration of Cl- ion in a solution, material compatibility is best determined through tests and experiments. The pump manufacturer can provide material recommendations based on the chemical name, concentration, and operating temperature of your chemical.
The flammability of the chemical will determine the type of pump used. For example, seal-less pumps are recommended for highly flammable liquids. An explosion-proof or a flame-proof motor may be required depending on the usage environment.