The velocity head for water flowing with a velocity of 1.5 m/s is 1.1 kPa. Typically the outlet nozzle on a centrifugal pump will have a higher velocity than that, but most installations have a reducer installed just downstream of the outlet and the velocity head is (mostly) recovered as pressure. So if your pump has a total head of 300 kPa the small amount of velocity head would be covered by the normal safety factors built into the system and it is often ignored.
However, if you are dealing with a high flow, low head installation then perhaps the velocity head is important. Most pipe sizing software will automatically calculate the velocity head for you, or if you are building a spreadsheet then just add in one more formula and you can be sure whether the velocity head is important or not every time.
The example they give has a velocity of 8.5m/sec where it makes ~5% difference, but again on a relatively low head output.
In general I would say that if your output pressure is more than 5 bar and velocity where you're measuring the pressure less than 4-5 m/sec, you can safely ignore it. - Katmars example is less than 0.3% of the head.
So just do it as a quick side calc (not exactly hard) and see if its > 1-2% of the pump head. If it is then add it in, if not just forget about it.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
It is the resistance to the pump's flow that is read on a pressure gauge attached to the discharge line.
For most pumping applications, the velocity is a small component of the pump head. However, for some pump applications with very high flows and low discharge heads, the velocity head may become important. See the example.
Katmar and LittleInch have presented the concept very well. I would like to add that I include velocity head when it is more than about 3% of static head. Less than that and it does not improve the quality of the decision you are trying to make. It is unlikely (but not impossible) for a velocity head less than 5% of the static head to cause you to have to add hp to the driver, which is the main reason I ever see for considering it (you might also have to consider velocity head when troubleshooting capacity issues, but it is nearly never the problem of not meeting a pump curve).
