Now its time to get to the heart of the hydronic system. There are to major catigories of pumps: positive displacement and centrifugal. Positive diplacement pumps come in three types: Piston, Rotary, and Screw. The centrifugal pump is by far the most common pump found in the air conditioning field. This type of pump is favored because of the following characteristics:
Simple construction, Fewer moving parts, Steady non-surging flow, Compact and lightweight, Can be connected to standard motors, Long life, Easy maintenance and minimum repair, and reasonable cost just to name a few.

There are many things to list that must been done to balance the flow through a pump.

• You must have the manufactures submittal data for the pump you are balancing. This data will have the pumps design head pressure, GPM, RPM, and impeller size.
• Make sure that the design pump GPM matches up equally with the chiller, boiler, or cooling tower design GPM that you are pumping water through. It is common to have a diversity factor, and a plan should be made to compensate for this during balancing.
• The system must be filled, flushed, and free of air and debris. Coil and pump strainers should also be cleaned prior to balancing.
• Inspect all manual and automatic valves for correct operation and drive them to the open position.
• Know what control changes that need to be made to balance the system. D.P. settings, automatic control valves stroked open, pump demands ect.
• Now we are ready to take our readings and plot them on a pump curve.