TOTAL HEAD

[gorkus]

is right the following formula in order to calculate the total head which must be able to developed the p.d pump.?

Hs= hd-hs mts
hd= hsd+hpd+hfd
hs=hss+hps-hfs

hps & hpd are 0 if tank are open = atmospheric pressure.
hf= fricction losses

 

[25362]

In estimating differential heads, there usually are four components:

velocity head, elevation head, static head and frictional head loss.

I have the feeling that the first one hasn't been considered. Usually small in comparison with the others, and sometimes cancelling out between suction and discharge, the velocity pressure, or head, is frequently neglected.

Should this not be so the velocity pressure (bar) would have to be computed, in SI units:

wV²/20,387g,​

where:

w = fluid specific mass , kg/m³
V = fluid velocity , m/s
g = gravity acceleration, m/s²

or as:

3.78(w/g)(Q/a)²,​

where:

Q = flow, m³/min
a = cross-sectional area perpendicu;ar to flow, mm²

This is concerning pumping differential or "total" pressure.

Then, depending on the type of pump, one has to consider other factors such as suction conditions (NPSH, fluid vapor pressure, acceleration pressures), pulsations, noise, etc.

NB: the formulas were taken from the Pump Handboook by Karassik et al. (McGraw-Hill).