One of the most important factor when inspect a pump is to find out the real Static Head or How much height that the pump can lift the fluid . ( See the CENTRIFUGAL PUMP (Advanced) to see how to calculate the pump Characteristics and Select a Pump)
During commissioning, an initial assessment the pump Head by reading the Discharging pressure gauge (P2 as above image, ex: 1 bar ~ 10 m height), and it’s not correct concept because of the Pump Head is not quite the same thing as a Discharge Pressure.
So what is the difference between pressure and head then?
While some pump manufacturers that use pressure (differential pressure which is measure the deviation between Suction and Discharge flange ~ HEAD) to characterize their pumps, this is not the most “accurate” way to do so (Because of friction and loss along the pipe line).
Head is useful because it evaluates a pump’s capacity to do a job. If you have to pump a liquid up to 10m and your pump doesn’t have at least 10m of head, then there is no chance it will work. Your pump will need at least 10m plus the friction loss to get the required flow at the discharge point.
Another interesting thing about head is it is independent of the type of fluid being pumped (assuming the viscosity is relatively low and similar to water). Whether you’re pumping water or a heavy caustic solution, the head achieved will be the same. The pressure at the discharge of the pump, however, will be higher for the heavier solution.
That’s why we would not be able to do simply looking at a pressure gauge and figure out what is pump’s discharge head ability is.
Hopefully this post reveal some light on the difference between head and pressure.