INTRODUCTION
This section briefly describes the main features of pumps and pumping systems.
What are pumps and pumping systems?
Pumping systems account for nearly 20% of the world’s electrical energy demand and range from 25-50% of the energy usage in certain industrial plant operations (US DOE, 2004).
Pumps have two main purposes:
1. Transfer of liquid from one place to another place (e.g. water from an underground aquifer into a water storage tank)
2. Circulate liquid around a system (e.g. cooling water or lubricants through machines and equipment)
The main components of a pumping system are:
a. Pumps (different types of pumps are explained in section 2)
b.Prime movers: electric motors, diesel engines or air system
c. Piping, used to carry the fluid
d. Valves, used to control the flow in the system
e. Other fittings, controls and instrumentation
f. End-use equipment, which have different requirements (e.g. pressure, flow) and therefore determine the pumping system components and configuration. Examples include heat exchangers, tanks and hydraulic machines.
PUMPING SYSTEM CHARACTERISTICS
1. Resistance of the system: head
Pressure is needed to pump the liquid through the system at a certain rate. This pressure has to be high enough to overcome the resistance of the system, which is also called “head”. The total head is the sum of static head and friction head:
a) Static head
Static head is the difference in height between the source and destination of the pumped liquid (see Figure 2a). Static head is independent of flow (see Figure 2b). The static head at a certain pressure depends on the weight of the liquid and can be calculated with this equation:
Head (in feet) = Pressure (psi) X 2.31 Specific gravity
Static head consists of:
1. Static suction head (hS): resulting from lifting the liquid relative to the pump center line.
The hS is positive if the liquid level is above pump centerline, and negative if the liquid level is below pump centerline (also called “suction lift)
2.Static discharge head (hd): the vertical distance between the pump centerline and the surface of the liquid in the destination tank.
b) Friction head (hf)
This is the loss needed to overcome that is caused by the resistance to flow in the pipe and fittings. It is dependent on size, condition and type of pipe, number and type of pipe fittings, flow rate, and nature of the liquid. The friction head is proportional to the square of the flow rate as shown in figure 3. A closed loop circulating system only exhibits friction head (i.e. not static head).
Static head Flow destination source Static head Electrical Energy Equipment: Pumps and Pumping Systems