Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Understanding Head

Up to now, we’ve been tossing around the

term headrather loosely. With regard to

pumps, head has a very specific and impor-

tant meaning. It is based on two interrelated

facts:

1 .It takes a known amount of power to

raise a given quantity of a specific fluid

a known distance.

2 .Head is equal to pressure in psi, kPa,

atmospheres, inches or mm of mercury

(Hg), and so on.

It thus becomes convenient to use head, in

feet or meters, in determining all the com-

bined resistances a pump has to work against

and so find the power required to pump fluid

through a given piping system. Since water

is the most common fluid pumped, we’ll dis-

cuss head in terms of feet or meters of fresh

water. Then to deal with other fluids, we’ll

apply adjustments as necessary.

Pumps, plumbing, and piping systems are

fantastically complex subjects. The third

edition of Pump Handbook (2000), edited by

Igor Karassik, Joseph Messina, Paul Cooper,

and Charles Heald, is about 2,500 pages, and

that is just one reference on the subject.

Again, what we’re doing here is taking a fairly

simple look at the basic (and relatively

straightforward) pump and piping systems

used aboard boats.

Static Head

Lift head or static head is the most obvious

type. In Figure 19-6, you can see the total

PART SIX:PLUMBING SYSTEMS WITH NOTES ON FIRE SUPPRESSION

Figure 19-6.
Static head with
negative suction
head