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Useful Pumping Data
Pump Heads
Piping
The size of pipe should not be smaller than the
pump ports and, for long pipe runs or when handling viscous
liquids should generally be larger. For other than very
simple pipe runs, the actual pipe losses should be calculated
using loss-of-head curves, as they may be a major part of the
total head on the pump. Easy bends should be used and
sharp elbows and tees avoided, to avoid loss of capacity or
difficulty in priming due to air leaks.
Net Positive Suction Head (NPSH)
NPSH available is the absolute pressure
of the liquid at the pump entry less its vapour pressure at the
pumping temperature. It is an expression of the service
conditions and is the maximum absolute pressure available at the
pump entry to overcome the suction losses of the pump itself.
NPSH required
is the minimum absolute
pressure necessary at the pump entry to maintain the required
flow without cavitation. The NPSH required for any pump is
the standard absolute atmospheric pressure (10.4 m or 34 ft of
water) less the listed suction lift of the pump at normal
temperature and pressure.
Specific Gravity
The specific gravity of a liquid is the ratio of
the weight of unit volume of the liquid to that of distilled
water at 4oC. For
normal pumping calculations, the specific gravity of clean fresh
water can be taken as 1, and that of sea water 1.03.
Viscosity
In the SI system of units,
dynamic viscosity is expressed as the Newton
second per square meter (N*s/m2.
In the CGS system of units, dynamic viscosity is expressed as
dyne second per square centimetre (dyne*s/cm2) which
is called a Poise.
The centipoise (cP), is a
hundredth of a Poise and is the most common unit for dynamic
viscosity. The dynamic viscosity for water at 20oC
(68oF) is approximately 1 cP.
Kinematic viscosity is
defined as the ratio of dynamic viscosity to density. The
most common unit for kinematic viscosity is the centistoke (cSt),
which is a hundredth of a Stoke. A Stoke is defined as 1
cm2/s and is taken from :
kinematic viscosity = dynamic
viscosity ÷ density = Poise ÷ g/cm3
Conversion Tables
|
Quantity |
| Imp gpm |
U.S. gpm |
m3/hr |
lt/min |
| 1 |
1.2 |
0.273 |
4.546 |
| 0.833 |
1 |
0.227 |
3.785 |
| 3.667 |
4.4 |
1 |
16.67 |
| 0.22 |
0.264 |
0.06 |
1 |
|
Volume |
| Imp gal |
U.S. gal |
litres |
m3 |
ft3 |
| 1 |
1.2 |
4.546 |
0.00455 |
0.161 |
| 0.833 |
1 |
3.785 |
0.00379 |
0.134 |
| 0.22 |
0.264 |
1 |
0.001 |
0.0353 |
| 220 |
264.2 |
1000 |
1 |
35.32 |
| 6.229 |
7.475 |
28.32 |
0.028 |
1 |
|
Pressure or Head |
| ft H2O |
lb/in2 |
m H2O |
kg/cm2 |
in Hg |
mm Hg |
| 1 |
0.434 |
0.305 |
0.031 |
0.881 |
22.42 |
| 2.307 |
1 |
0.703 |
0.07 |
2.036 |
51.71 |
| 3.281 |
1.422 |
1 |
0.1 |
2.896 |
73.55 |
| 32.81 |
14.22 |
10 |
1 |
28.96 |
735.5 |
| 1.133 |
0.491 |
0.345 |
0.035 |
1 |
25.4 |
| 0.045 |
0.019 |
0.014 |
0.001 |
0.039 |
1 |
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