Actual rate of flow achieved by any centrifugal pump is based upon the system’s physical layout, the fluid viscosity, pipe friction which depends upon pipe diameter and length, the difference of elevation between the source and destination of fluid. During the selection process, one must also take into account the NPSHA and necessary power requirement for driving the pump. Any positive displacement pump selected properly can produce the rated flow in any physical environment.
- Pump size selection
For deciding the size for selecting any centrifugal sanitary Valves, first you must determine its flow rate. For any brewery process, pipe diameter is very important factor for determining its flow rate. Most of the fluid transfer operations performance are best within any range of selected fluid velocities for achieving nonturbulent flow and also reduce friction pressure loss. The maximum velocity depends on pipe size, fluid viscosity and fluid density.
- Determine your total head
Static head is nothing but the difference of height between the surface of fluid in suction tank and discharge tank. The friction head will depend upon the flow rate, the liquid viscosity and the pipe length. This is based on calculation from the values that are listed in tables for water or other viscous liquids. Total differential head will be the pressure that your pump needs to generate for delivering the necessary flow rate and is total sum of static head and friction head.
The NPSHA is considered as difference between the absolute pressure of pump suction and liquid vapor pressure found at the actual pumping temperature. For proper operation of pump, the pressure available at the NPSHA should exceed vapor pressure for maintaining the liquid phase. Any cavitation may occur as the vapor pressure will exceed the pressure near the pump suction, also the vapor bubbles gets formed in the liquid. As a result, there is a pump efficiency loss and also possible pump damage. Therefore, pump manufacturers will supply NPSHR for each pump.
- Pump power
The pump driver is usually any diesel engines, steam turbine or electric motor which is sized by calculating the power necessary with the formulae:
Pump power = (total differential head x flow rate x acceleration because of gravity x liquid density) ÷ pump efficiency.
- Selection of pump
The pump is usually selected by looking at the information of any manufacturer’s catalog, where you need to see the total flow and head needed, the pump power needed, NPSHR and the type of pump suitable for your application.