Quel est le NPSH requis pour une pompe Warman 350L avec un débit volumétrique de 1400 m3/h à 2800 m3/h et une pression de 2 à 5 bar ?

NPSH
(Net Positive Suction Head)
Concept & Calculations
Educational Course

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NPSH – Concept and Calculations
1. NET POSITIVE SUCTION HEAD:
The NPSH called as the Net Positive Suction Head is a necessary calculation whenever
an installation of a pump is designed in order to prevent cavitation for safe and reliable
operation of the system.
The suction gauge is defined as the absolute feet taken on the suction nozzle corrected
to pump centerline, minus the Vapor Pressure in feet absolute corresponding to the temperature
of the liquid, plus Velocity Head at this point. There are two conditions to calculate
an NPSH pumping system, as described below:
a. Available NPSH - NPSHa:
NPSHa: C alled as Available Net Positive Suction Head is the normal operation head
determined during design and construction or determined experimentally from a physical
system.
b. Required NPSH - NPSHr:
NPSHr: Called as Required Net Positive Suction Head is the maximum head required
by the pump in order to prevent cavitation for safe and reliable operation of the pump.
Generally is determined experimentally by the pump manufacturer and is part of the documentation
of the pump with a graphic named pump curve as the example below.








Note: The available NPSHa of the system should always exceed the required NPSHr of the
pump to avoid vaporization and cavitation of the impellers and pump inner walls. The
NPSHa is also calculated to avoid that head loss in the suction pipe and in the pump casing
, local velocity accelerations and pressure decreases, start boiling the fluid on the impeller
surface.

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Obs.: Note that the required NPSHr increases with the square capacity. Pumps with dou-
ble-suction impellers have lower NPSHr than pumps with single-suction impellers. A pump
with a double-suction impeller is considered hydraulically balanced but is susceptible to
an uneven flow on both sides with improper pipe-work. The terms commonly used to calculate
the NPSH in pumping systems are:

2. STATIC HEAD:

Static head: Is measured from the liquid level to the centerline of the pump. If the liquid
level is above the pump centerline you will have a positive number. If the level is below
the centerline you will have a negative number.
3. PRESSURE HEAD:
Atmospheric pressure: Is 14.7 psi at sea level to be converted to feet, using a formula
to the static head where ever you have an open tank. If the fluid is under vacuum
we can convert to the absolute pressure reading to head instead of atmospheric pressure.
Vacuum is often read in inches of mercury so you will need a formula to convert it to
head. Here is the formula:

Feet of liquid = 1.133 x inches of mercury
Specific gravity
4: TOTAL DYNAMIC HEAD:
Total Dynamic Head: I s the vertical distance between the source of supply and the
point of discharge when pumping at required capacity increases the velocity head, friction
, inlet and exit losses, divided in two conditions: Total Dynamic Discharge Head is
the Total Dynamic Head minus Total Dynamic Suction Head.
a. Total Dynamic Discharge Head: Is determined on tests where Suction Head exists.
It is the reading of the gauge attached to the discharge nozzle of pump, minus the reading
of a gage connected to the suction nozzle of pump, plus or minus vertical distance
between centers of gauges (depending upon whether suction gage is below or above discharge
gage), plus excess, if any, of the Velocity Head of discharge over Velocity Head of
suction as measured at points where instruments are attached.
b. Total Dynamic Suction Head: Is also determined on tests where Suction Head exists
and also divided in three conditions:
1. SUCTION LIFT:
a. Suction Lift: Exists when the suction is measured at the pump nozzle and then corrected
to the centerline of the pump, below atmospheric pressure.

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b. Static Suction Lift: Is the vertical distance from the free level or source of the supply
system, to the center line of a pump.
c. Dynamic Suction Lift: Is also determined on tests, is the reading of the mercury col-
umn connected to suction nozzle of pump, plus vertical distance between point of attachment
of mercury column to centerline of pump, plus head of water resting on mercury
column, if any.
2. SUCTION HEAD:
a. Suction Head: Exists when the pressure measured at the suction nozzle and then cor-
rected to the centerline of the pump is above the atmospheric pressure (sometimes also
called Head of Suction).
b. Static Suction Head: Is the vertical distance from the free level of the source of sup-
ply to centerline of pump.
c. Dynamic Suction Head: I s the vertical distance from the source of supply, when
pumping at required capacity, to centerline of pump, minus Velocity Head, entrance, friction
, but not minus the internal pump losses.
Note: The Dynamic Suction Head, determined by tests, is the reading of a gage connect-
ed to suction nozzle of pump, minus vertical distance from center of gage to centerline of
pump. The Suction Head, after deducting the various losses, may be a negative quantity,
in which case a condition equivalent to Suction Lift will prevail.
3. VELOCITY HEAD:
The Velocity Head: Sometimes also called as "Head due to Velocity" of water with
a given Velocity, is the equivalent head through which it would have to fall to acquire
the same Velocity: or the head merely necessary to accelerate the water. Knowing the
velocity, we can readily figure the Velocity Head from the simple formula:
v2
h = =
2.g
Where "g" is acceleration due to gravity 9.80665 m/s2 (~32.1740 ft/s2) or knowing the
head (h). And thus obtain the velocity head:
v² = 2.g. h
Obs.: The Velocity Head is a factor figuring the Total Dynamic Head, but the value is
usually negligible; however, it should be considered when the Total Head is low and when
the Suction Lift is high. Where the suction and discharge pipes are the same size, it is
only necessary to include in the Total Head the Velocity Head generated in the suction
piping.
If the discharge piping is of different size than the suction piping, which is often the ease,
then it will be necessary to use the Velocity in the discharge pipe for computing the Velocity
Head rather than the Velocity in the suction pipe.

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In testing a pump, a vacuum gauge or a “mercury column” is generally used for obtaining
Dynamic Suction Lift. The mercury column or vacuum gage will show the Velocity
Head combined with Entrance Head, Friction Head, and Static Suction Lift.
On the discharge side, a pressure gage is usually used, but a pressure gage will not indicate
the Velocity Head and therefore be obtained either by calculating the Velocity or taking
readings with a Pitometer.
The Velocity varies considerably at different points in the cross section of a stream. It is
important in using the Pitometer to take a number of readings at different points in the
cross section.
Table 1. VELOCITY – VELOCITY HEAD:
Velocity Velocity Velocity Velocity Velocity Velocity Velocity Velocity
in Head in Head in Head in Head
feet/ sec. in ft. feet/ sec. in ft. feet/ sec. in Ft. feet/ sec. in Ft.
1.0 0.02 6.0 0.56 9.5 1.4 12.0 2.24
2.0 0.06 7.0 0.76 10.0 1.55 13.0 2.62
3.0 0.14 8.0 1.0 10.5 1.7 14.0 3.05
4.0 0.25 8.5 1.12 11.0 1.87 15.0 3.50
5.0 0.39 9.0 1.25 11.5 2.05

Static Suction Head (H): Is positive when liquid line is above pump centerline and
negative when liquid line is below pump centerline, as can be seen at the sketch below.










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Note: See the tables indicating the energy loss due friction for water flow through
ASME/ANSI B36.10 schedule 40 steel piping and fittings. The friction loss can be
also calculated by, f (loss) = K x v²/2g (g = 32.17 ft/s²).
Imperial and Metric relations:
 1 foot of head = 0.433 psi = 0.030kg/cm²
 1 psi = 2.31 feet (water) = 0.0703 kg/cm²
TABLE 02.a – WATER VAPOR PRESSURE CHART, psia:
Water Vapor
Temperature
Pressure
F° C° psia
40 4.4 0.1217
50 10 0.1781
60 15.6 0.2563
70 21.1 0.3631
80 26.7 0.5069
90 32.2 0.6982
100 37.8 0.9492
110 43.3 1.275
120 48.9 1.692
130 54.4 2.223
140 60 2.889
150 65.6 3.718
160 71.1 4.741
170 76.7 5.992
180 82.2 7.510
190 87.8 9.339
200 93.3 11.50
212 100 14.70

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TABLE 02.b = SUCTION HEAD – TEMPERATURE – WATER VAPOR PRESSURE:
Temperature Abs. Water Vapor Pressure Max. Elevation
C° F° psi/psia bar (m) (ft)
0 32 0.0886 0.0061 0.062 0.2044
5 40 0.1217 0.0084 0.085 0.2807
10 50 0.1781 0.0122 0.125 0.4108
15 60 0.2563 0.0176 0.180 0.5912
21 70 0.3631 0.0250 0.255 0.8376
25 77 0.4593 0.0316 0.322 1.0594
30 86 0.6152 0.0424 0.432 1.4190
35 95 0.8153 0.0562 0.573 1.8806
40 104 1.069 0.0737 0.751 2.4658
45 113 1.389 0.0957 0.976 3.2040
50 122 1.789 0.1233 1.258 4.1267
55 131 2.282 0.1573 1.604 5.2639
60 140 2.888 0.1991 2.030 6.6618
65 149 3.635 0.2506 2.555 8.3849
70 158 4.519 0.3115 3.177 10.424
75 167 5.601 0.3861 3.938 12.9199
80 176 6.866 0.4733 4.827 15.8379
85 185 8.398 0.5790 5.904 19.3718
90 194 10.167 0.7010 7.148 23.4524
95 203 12.257 0.8450 8.618 28.2735
100 212 14.695 1.0132 10.332 33.8973


Viscosity: I s the internal friction of a liquid tending to reduce flow. Viscosity is defined
by instruments termed as Viscosimeters of which there are several types as Saybolt
Universal and Redwood.
Obs.: In the United States the Saybolt Universal is in general use with few exceptions.
Viscosity is expressed as the number of seconds required for a definite volume of fluid
under an arbitrary head to flow through a standardized aperture at constant temperature.


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5. SPECIFIC GRAVITY:
Specific Gravity (S.g): Is t he ratio of the weight of any volume to the weight of an
equal volume of some other substance taken as a standard at stated temperatures. As
an example, for solids or liquids the standard is usually water, and for gases the standard
is air or hydrogen.

TABLE 03 = PRESSURE AND EQUIVALENT FEET HEAD OF WATER
PSI or Feet PSI or Feet PSI or Feet PSI or Feet
Lb/sq. in. Head Lb/sq. in. Head Lb/sq. in. Head Lb/sq.in. Head
1.0 2.31 20.0 46.28 120.0 277.07 225.0 519.51
2.0 4.62 25.0 57.72 125.0 288.62 250.0 577.24
3.0 6.93 30.0 69.27 130.0 300.16 275.0 643.03
4.0 9.24 40.0 92.36 140.0 323.25 300.0 692.69
5.0 11.54 50.0 115.45 150.0 346.34 325.0 750.41
6.0 13.85 60.0 138.54 160.0 369.43 350.0 808.13
7.0 16.16 70.0 161.63 170.0 392.52 375.0 865.89
8.0 18.47 80.0 184.72 180.0 415.61 400.0 922.58
9.0 20.78 90.0 207.81 190.0 438.90 500.0 1154.48
10.0 23.09 100.0 230.90 200.0 461.78 1000.0 2310.00
15.0 34.63 110.0 253.98


TABLE 04 = FEET HEAD OF WATER AND EQUIVALENT PRESSURE
Feet PSI or Feet PSI or Feet PSI or Feet PSI or
Head Lb/sq. in. Head Lb/sq. in. Head Lb/sq. in. Head Lb/sq. in.
1.0 0.45 30.0 12.99 140.0 60.63 300.0 129.93
2.0 0.87 40.0 17.32 150.0 64.96 325.0 140.75
4.0 3 1.73 1.30 60.0 50 21.65 25.99 170.0 160 73.63 69.29 400.0 350 173.24 151.58
5.0 2.17 70.0 30.32 180.0 77.96 500.0 216.55
7.0 6 3.03 90.0 38.98 200.0 86.62 700.0 303.16
2.60 80 34.65 190 82.29 600 259.85
8.0 3.46 100.0 43.31 225.0 97.45 800.0 346.47
10.0 9 4.33 120.0 51,97 275.0 119.10 1000.0 433.09
3.90 110 47.65 250 108.27 900 389.78
20.0 8.66 130.0 56.30


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TABLE 05 = ALTITUDE AND ATMOSPHERIC PRESSURE
ALTITUDE AT SEA LEVEL ATMOSPHERIC PRESSURE
Feet Meters Psia Kg/cm² abs.
0.0 0.0 14.69 1.033
500.0 153.0 14.43 1.015
1000.0 305.0 14.16 0.956
1500.0 458.0 13.91 0.978
2000.0 610.0 13.66 0.960
2500.0 763.0 13.41 0.943
3000.0 915.0 13.17 0.926
3500.0 1068.0 12.93 0.909
4000.0 1220.0 12.69 0.892
4500.0 1373.0 12.46 0.876
5000.0 1526.0 12.23 0.860
6000.0 1831.0 11.78 0.828
7000.0 2136.0 11.34 0.797
8000.0 2441.0 10.91 0.767
9000.0 2746.0 10.50 0.738
10000.0 3050.0 10.10 0.710
15000.0 4577.0 8.29 0.583
TABLE 06 = PRACTICAL SUCTION LIFTS - ELEVATIONS ABOVE SEA LEVEL
Barometer Theoretical Practical Vacuum
ELEVATION Reading Suction Lift Suction Gauge*
Lift
Psi Feet Feet Inches
At sea level 14.7 33.9 22 19.5
¼ mile – 1320 ft – above sea level 14.0 32.4 21 18.6
½ mile – 2640 ft – above sea level 13.3 30.8 20 17.7
¾ mile – 3960 ft – above sea level 12.7 29.2 18 15.9
1 mile – 5280 ft – above sea level 12.0 27.8 17 15.0
1 ¼ mile – 6600 ft – above sea level 11.4 26.4 16 14.2
11/4 mile – 7920 ft – above sea level 10.9 25.1 15 13,3
2 miles – 10560 ft – above sea level 9.9 22.8 14 12.4
NOTES:
1. Multiply barometer in inches by 0.491 to obtain psi. *Vacuum gauge readings inches correspond
to suction lift in feet only when pump is stopped. Pipe friction increases the vacuum gauge
readings when pump is running. For quiet operation, vacuum gauge should never register more
than 20 inches when pump is running.
2. When pumping volatile liquids as gasoline and naphtha, special consideration to the amount
of suction lift and the size of the suction pipe. The suction lift, the pipe line friction should
never exceed 12 feet.
3. For liquids such as lube oil, molasses, etc., a suction lift up to 24 feet, sea level, is usually
satisfactory.

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TABLE 07 = EQUIVALENT VALUES OF PRESSURE
Inches of Feet of psi Inches of Feet of psi Inches Feet of psi
Mercury Water Mercury Water of Water
Mercury
1.0 1.13 0.49 11.0 12.44 5.39 21.0 23.75 10.28
2.0 2.26 0.98 12.0 13.57 5.87 22.0 24.88 10.77
3.0 3.39 1.47 13.0 14.70 6.37 23.0 26.00 11.26
4.0 4.52 1.95 14.0 15.83 6.85 24.0 27,14 11.75
5.0 5.65 2.45 15.0 16.96 7.34 25.0 28.27 12.24
6.0 6.78 2.94 16.0 18.09 7.83 26.0 29.40 12.73
7.0 7.91 3.43 17.0 19.22 8.32 27.0 30.53 13.22
8.0 9.04 3.92 18.0 20.35 8.82 28.0 31.66 13.71
9.0 10.17 4.40 19.0 21.48 9.30 29.0 32.79 14.20
10.0 11.31 4.89 20.0 22.61 9.79 29.92 33.83 14.65

6. DISTANCE TO WATER LEVEL EQUIPMENT:
Example: Install a small pipe or tubing (about 1/8 inches or 1/4 in) in a well. The exact
length must be carefully measured. The end of the air pipe should extend to the bottom
of the pump suction. Install a reliable pressure gauge, so that the exact air pressure in
pounds may be shown, when the hand pump is operated.
Solution: Attach the hand tire-pump and fill pipe until further pumping can not increase
the reading on the gauge. Multiply the reading in pounds by 2.31, and subtract the re-
sult from the length of air pipe. The difference will be the distance from the center of the
pressure gauge face to the surface of the water. Any horizontal distance of the pipeline
from the well opening has no effect on the result.
Example: An air pipe is 100 feet long from center of gage face to bottom end of pipe.
The highest pressure reading is 18 pounds, then, 18 x 2.31 = 41.58 feet of lift.
 41.58 – 100 = 58.42 - showing that the water level is 58.42 feet below center
of pressure gage.
 Doubling the diameter of pipe or cylinder increases its capacity four times.
Friction of liquids in pipes increases with the square of the velocity.
 Atmospheric pressure at sea level is 14.7 pounds per square inch. This
pressure with perfect vacuum will maintain a line of mercury 29.9 inches or a
column of water 33.9 feet high.
 In practice, however, pumps should not have a total dynamic suction lift greater
than 26 feet.

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7. HOW TO CALCULATE THE NPSH OF A PUMP:
First determine if you are going to have a cavitation problem, you will need access to
several additional parts of information:
 The pump curve is going to show you the Net Positive Suction Head (NPSH)
required at a given capacity. Keep in mind that this NPSH required tables are for
cold and fresh water.
 A chart or some type of publication will give you the vapor pressure of the fluid
you are pumping.
 You need to know the specific gravity of your fluid. The number is temperature
sensitive. You can get this number from a Temperature – Pressure chart.
 Find the charts showing the head loss through the size of piping and charts to
calculate the loss for fittings, valves and accessories.
 Find the atmospheric pressure at the time you are making your calculation. The
atmospheric pressure changes throughout the day, but the calculations have to
start somewhere.
 The formulas for converting pressure to head and head back to pressure in the im-
perial system are as follows:

Pressure = head x Sg
2.31
Head = pressure x 2.31
Sg
Where:
Sg = Specific Gravity;
Pressure = pounds per square inch, psi;
Head = feet
You also need to know the formulas that show you how to convert vacuum readings to
feet of head. Here are a few of them:
Inches of mercury x 1.133 / specific gravity = feet of liquid;
Pounds per square inch x 2.31 / specific gravity = feet of liquid;
Millimeters of mercury / (22.4 x specific gravity) = feet of liquid.
It is necessary to know the conditions below, using a pump graphic as shown below:
NPSHa > NPSHr = NPSH available (calculated) > NPSH required (pump curve).



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a. Calculations using the following conditions:
NPSHa = +-H + Pa – Pv – Hf =
H = Static Suction Head (positive when liquid line is above pump centerline, nega-
tive when liquid line is below pump centerline).
Pa = Atmospheric pressure with installed pump according to altitude from sea lev-
el (see table 05) – converting to head - suction pressure x 2.31/Sg
Pv = Vapor pressure according to temperature of water (see table 02) - convert-
ing to head - vapor pressure x 2.31/Sg = Total feet.
Hf = See tables indicating friction loss for water flow through ASME/ANSI B36.10
schedule 40 steel piping. Fittings friction loss = K x v²/2g (g = 32.17 ft/s²).
Obs.: The ANSI/ASME codes or the Hydraulic Institute Standards is the source for pres-
sure head loss K coefficients:
Application Example – Water Pumping:
 Fluid: Water;
 Pipe: Steel Pipe - Schedule 40;
 Temperature: 20.0 oC (68.0 oF);
 Density: 998.3 kg/m3 (62.0 lb/ft3);
 Kinematic Viscosity: 1.004. 10-6 m2/s (0.01 stokes) (1.08. 10-5 ft2/s);
 Pipe Roughness Coefficient: 4.5. 10-5.

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b. Examples for calculation:
1. Find the NPSHa from below data:
H = Liquid level above pump centerline = +5 feet;
Pa = Atmospheric pressure = 14.7 psi - the tank is at sea level;
Suction and Discharge piping = 2 inch diameter, plus two 90° regular screwed
elbow = total length = 10 feet;
Pumping =100 gpm @68°F – 10 ft/s as maximum velocity;
Pv = Vapor pressure of 68°F water = 0.339 psia (see table 02);
Sg = Specific gravity = 1.0 (fresh cold water);
NPSHr (net positive suction head required, as per the pump curve) = 9 feet.
NPSHa = Static head + Atmospheric
pressure (converted to
head) + Vapor pressure of the fluid
(converted to head) – Friction
loss (in the piping, valves and fittings
);
NPSHa = +-H + Pa – Pv – hf =
H - Static head = +5 feet.
Pa - Atmospheric pressure =
pressure x 2.31/Sg. = 14.7 x
2.31/1 = +34 feet absolute.
Pv - Vapor pressure of water at
68°F - pressure x 2.31/Sg =
0.339 x 2.31/1 = 0.78 feet.
Hf - Looking at the friction charts: 100 gpm - flowing through 2 inch pipe
shows a loss of 17.4 feet for each 100 feet of pipe, then:
Piping friction loss = 17.4/10 = 1.74 feet.
Fittings friction loss = K x v²/2g = 0,57 x 10² (x 2) = 1.77.
2 x 32.17
Total friction loss for piping and fittings = Hf = 1.74 + 1.77 = 3.51 feet.
a. NPSHa (available) = +-H + Pa – Pv – Hf =
b. NPSHa (available) = +5 + 34 - 0.78 – 3.51 =
c. Solution = 34.7 feet (NPSHa) > 9 feet (NPSHr).
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The pump curve showed an NPSHr of only 9 feet of head at 100 gpm. According to above
calculation we have NPSHa (available) = 34.7 feet. So, we have plenty to spare.
2. Using the same data above, find the NPSHa in metric numbers:
H = Liquid level above pump centerline = +1.5 m
Pa = Atmospheric pressure = 1.033 kg/cm² = at sea level
Suction and discharge piping 2 in with two 90° regular screwed elbow = 3 m
Pumping flow – 100 gpm = 0.379 m³/min (22.7 m³/h) at 20º C (68º F)
Maximum speed for a 2 in piping – 10 ft/s = 3.0 m/s
Pv = Vapor pressure at 20º C = 0.024 kg/cm² (see table 02)
Sg – Specific gravity = 0.998 (use 1.0) = 1000 kg/m³ (apparent water density)
NPSHr (net positive suction head required, from the pump curve) = 2.75 m
1) Converting Pa =1.033 kg/cm² in kg/m²:
1.033 kg/cm² x 10,000 = 10,330 kg/m².
Water density 1000 kg/m³ = 10,330 kg/m2 = 10.33 m of water column (mwc)
1000 kg/m³
2) Converting Pv = 0.024 kg/cm² in kg/m² = 0.024 kg/cm² x 10,000 = 240 kg/m²:
Water density 1000 kg/m³ = 240 kg/m2 = 0.24 m of water column (mwc)
1000 kg/m³
3) Calculating Hf - Piping 2 in total length = …………………………………..3.0 m
Equivalent 2 in elbows length = 1.0 m (x 2) = …2.0 m
Total equivalent length = …………………………………..5.0 m
According to metric tables: for 22.7 m³/h using piping diameter 2 inches and length of
100.0 m, the total friction loss is considered = ~25%, then:
5.0 m x 0.25 = 1.25 m
Then:
a. NPSHa = +-H + Pa – Pv – hf =:
b. NPSHa = +3.0 + 10.33 – 0.24 – 1.25 = 11.84 m (NPSHa) > 2.75 m (NPSHr).
c. Solution: The pump curve showed an NPSHr of only 2.75 m of head at 22.7 m³/h.
According to above calculation we have NPSHa (available) = 11.84 m. So, we have
plenty to spare.


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Important Conversions:
Convert to
Convert from
m3/s m3/min m3/h liter/sec liter/min liter/h

US gpm 0.000063 0.00379 0.227 0.0630 3.785 227.1
cfm 0.00047 0.028 1.699 0.472 28.32 1698.99

3) Net Positive Suction Head, according to the following data below:
Fluid: Water – Static Suction Lift = 15 ft; Static Discharge Head = 7.5 ft.
NPSHr – according to performance pump curves = 5.0 ft
Atmospheric pressure - corrected = 6 ft
Safety factor for atmospheric pressure = 2.0 ft
a) How to compute the Total Dynamic Head (see tables below):
A STATIC SUCTION LIFT 15 ft
B Friction, Suction (see tables):
a) Pipe diameter, 4”
Pipe total length = 17 ft
b) One elbow 90º, diameter, 4” = 6 ft
c) One elbow 45º, diameter, 4” = 4 ft
Fittings total length = 10 ft
Total equivalent length = 27 ft
d) Pipe friction loss (see tables) = 4.43 ft
e) Friction loss = 27’ x 4.43/100 = ~1.20 ft
f) Correction factor = 0.71
Total friction loss, Suction Lift = 1.20 x 0.71 ………………= 0.85 ft
C Total Dynamic Suction Lift = (15 + 0.85) ……………………= 15.85 ft
D STATIC DISCHARGE HEAD 7,5 ft
E Friction, Discharge (consult tables):
a) Pipe diameter, 4”
Pipe total length = 500 ft
b) One elbow 90º, diameter, 4” = 6 ft
c) One check valve, diameter, 4” = 27 ft
d) One gate valve, diameter, 4” = 6 ft
Fittings total length = 37 ft
Total equivalent length = 537 ft
e) Pipe friction loss (table) = 4.43 ft
f) Friction loss = 537 x 4.43/100 = 23.8 ft
g) Correction factor = 0.71
Total friction loss, Discharge = 23.8 x 0.71 …………………= 16.9 ft
F Total Dynamic Discharge Head = (16.9 + 7.5) ……………= 24.40 ft
Total Dynamic Head – C + F = (15.85 + 24.4) …………………= 40.25 ft

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b) How to compute the NPSHa:
G Atmospheric pressure at sea level = 33.90'
H Atmospheric pressure - corrected = - 6.00’
I Atmospheric pressure available at job site…………………. =
+27.90'
J Deductions from available atmospheric pressure:
1. Total dynamic suction lift…………………………… = -15.85'
2. Vapor pressure 74° (0.441 x 2.31 = 1.0’)= -1.00'
3. Safety factor (for atmospheric pressure) = -2,00’
K Net deductions from available atmospheric pressure…….. -18.85’
L NPSHa (available) = (27.9’ – 18.85)……..…………………………………= = + 9.05’
M NPSHr (required)…………………………………………………………………………= - 5.00’
N NPSH excess or excess atmospheric pressure……………………………= 4.05’
c. Solution: NPSHa (9.05’) > NPSHr (5.00’) - See the sketch below:
-18,85
















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REFERENCES:
Centrifugal Pumps- University of Sao Paulo, Engineering Lab
Gorman-Rupp - Pumps and Pumping Systems Catalog
Engineeringtoolbox.com – NPSH Tables
Fluid Mechanics – Munson, Young, Okiishi, 4th Edition, 2004
Hydraulics – Horace W. King, 4th Edition, 1945
Additional technical information, visit the following websites:
1. The Hydraulic Institute Standards at: www.pumps.org.
2. Pumps for process and chemical services - ASME B73.1 Standards.
3. Pumping equipment at www.pumpingequipmenttrade.com
Other Links:
http://www.tasonline.co.za/toolbox/pipe/veldyn.htm
http://docs.engineeringtoolbox.com/documents/797/hazen-williams-equation.xls
http://www.lightmypump.com
http://www.mcnallyinstitute.com/













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