Steps For Selecting A Submersible Pump

List basic data:
1. Characteristics of the medium: name, specific gravity, viscosity, corrosiveness, toxicity, etc.
2. Diameter and content (mass or volume percentage) of solid particles in the medium.
3. Medium temperature (°C).
4. Required flow rate.
For general industrial pumps, leakage within the piping system can be ignored during process operations, but the impact of process variations on the flow rate must be considered. For agricultural pumps utilizing open-channel water conveyance, seepage and evaporation losses must also be taken into account.

5. Pressure: Pressures at the suction tank and discharge tank; pressure drop (head loss) within the piping system.
6. Piping system data (pipe diameter, length, types and quantities of fittings, geometric elevation difference between suction and discharge tanks, etc.). If necessary, a system characteristic curve should be plotted. When designing the piping layout, consider the following:
A. Reasonable selection of pipe diameter: A larger diameter results in lower flow velocity and lower resistance loss at a given flow rate, but entails higher costs. A smaller diameter causes a sharp increase in resistance loss, requiring a pump with higher head and power, thereby increasing both initial investment and operating costs; therefore, a comprehensive technical and economic evaluation is required.
B. Discharge pipes and their fittings must be rated to withstand the maximum possible pressure.
C. Piping layout: Use straight runs as much as possible; minimize the number of fittings and the total pipe length. Where turns are necessary, the bend radius should be 3 to 5 times the pipe diameter, and the angle should be greater than 90° whenever possible.
D. Valves (e.g., ball valves or globe valves) and check valves must be installed on the pump discharge side. The valve regulates the pump's operating point, while the check valve prevents reverse flow (which could cause the pump to spin backwards and suffer damage from water hammer-a phenomenon where backflow generates immense reverse pressure).

 

Determining Flow Rate and Head
Determining Flow Rate
a. If the production process specifies minimum, normal, and maximum flow rates, the design should be based on the maximum flow rate.
b. If only the normal flow rate is specified, a margin should be included: for high-flow, low-head pumps with a specific speed ($n_s$) > 100, use a 5% margin; for low-flow, high-head pumps with $n_s$ > 50, use a 10% margin; for pumps with $50 \le n_s \le 100$, use a 5% margin; and for pumps of poor quality or those operating under harsh conditions, use a 10% margin.
c. If the basic data provides only mass flow rate, it must be converted to volumetric flow rate.