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Factors Affecting Pump Selection Overview

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INTRODUCTION

THE FOLLOWING EXPLANATIONS AND EXAMPLES ARE TO INTENDED TO ASSIST IN THE CORRECT SELECTION OF A SUBMERSIBLE PUMP FOR A CUSTOMER SPECIFIED SYSTEM. ALL ‘DYNAMIC HEAD’ CALCULATIONS ARE BASED ON A SYSTEM DESIGN FROM THE PACKER MANIFOLD OUTLET TO THE DISPENSER SHEAR VALVE ONLY.

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IT IS IMPORTANT TO NOTE THAT THE DISPENSER FRICTION HEAD AFFECTS THE OPERATION OF THE SYSTEM AND WILL BE REQUIRED TO

BE ADDED TO THE FINAL CALCULATION BY THE SITE DESIGNER. THE DISPENSER FRICTION HEAD IS OBTAINABLE FROM THE DISPENSER MANUFACTURER AND MAY BE IN EXCESS OF 20 METRES AT 40 LPM

FLOW FROM NOZZLE.


MAJOR FACTORS WHICH MAKE UP THE TOTAL DYNAMIC HEAD (TDH)


DYNAMIC HEAD

The TOTAL DYNAMIC HEAD is the total lift in metres of head that has to be overcome by the pump in order to achieve the dispenser manufacturer’s required flow rate at the dispenser shear valve. It is found by adding together the STATIC HEAD and the DYNAMIC HEAD.

SHEAR VALVE

STATIC HEAD


DEFINITIONS AND EXAMPLES

STATIC HEAD: The static head of liquid required to be lifted by the mersible pump as measured vertically from the tank mid-point to the dispenser shear valve. The unit of measurement is metres.

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STATIC HEAD – 4 metres

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In this example the Static Head is 4 metres. This head is roughly equivalent to 4 psi or 0.275 bar.

Factors Affecting Pump Selection Overview DYNAMIC HEAD: The head required to overcome the friction (resistance) to flow in the pipe and fittings. It is dependent upon:

a) the pressure required at the shear valve as specified by the Dispenser Manufacturer b) the diameter and length of the pipe required between the pump outlet and shear valve c) the type of piping and the type and number of fittings (elbows, valves, etc) d) the Specific Gravity (SG) of the liquid.

FRICTION HEAD INCREASES LOGARITHMICALLY WITH AN INCREASE IN FLOW RATE

(see graph below). From the graph:- the friction head at a flow rate of 200 lpm through 50 mm diameter pipe is 2.5 metres per 30 metres of piping and for a flow rate of 100 lpm the friction head is 0.6 metres.



Friction He a d For 50 m m Sm ooth Bore P ipe

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1

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0 25 50 75 100 125 150 175 200 225 250 275 300 325 350

Flow Rate (LPM)

Fric

tion

Hea

d (m

etre

s pe

r 30m

leng

th)

From the graph:- the friction head at a flow rate of 200 lpm through 50 mm diameter pipe is 2.5 metres per 30 metres of piping and for a flow rate of 100 lpm the friction head is 0.6 metres.



FRICTION HEAD DECREASES LOGARITHMICALLY WITH AN INCREASE IN PIPE DIAMETER.

This measurement is obtained from Friction Loss Curves that plot flow

rate against friction loss for a particular pipe type and diameter (see example below).



Friction Head Curves For & 50 mm Smooth Bore Pi

30 metres in Length

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0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300

Flow Rate (LPM)

Fric

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Hea

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etre

s)

38 mmpes,

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F ric tio n H ead C u rves F o r & 50 m m S m o o th B o re P

30 m etres in L en g th

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0 2 2 0 2 4 0 2 6 0 2 8 0 3 0 0

F low R ate (LP M )

Fric

tion

Hea

d (m

etre

s)

38 m mip es,

Compare the difference in Friction Head per 30 metres of length for the two pipe sizes at different flow rates:

160 lpm ( 1 metre and 5 metres = 4 metres) 240 lpm ( 4.9 metre and 39.9 metres = 35 metres)



EXAMPLE:

3 Dispensers - Number of nozzles = 6.

Pipe diameter = 50 mm (2 inch)

Flow rate required at each nozzle = 40 lpm.

Maximum flow rate = 6 x 40 = 240 lpm.

Design for 4 nozzles in use = 4x 40 =160 lpm



PIPE SECTIONS (A – F) WITH FLOW RATES


Factors Affecting Pump Selection Overview Friction head for each pipe section =

length of pipe x friction loss @ flow rate in that section (from graph) 30m

PIPE SECTION & LENGTH (Metres)

FLOW RATE (LPM) FRICTION HEAD (Metres) (pipe diam. 38 mm)

FRICTION HEAD (pipe diam. 50 mm)

A (30) 160.0 5 1.4 B ( 6) 106.7 1.3 0.6 C ( 6) 53.3 0.5 0.25 D (2) 53.3 0.5 0.25 E (2) 53.3 0.5 0.25 F (2) 53.3 0.5 0.25

Total Head 8.3 metres 3.0 metres Suggested pipe sizes (colour highlighted) would give a total friction head of 4 metres. EXAMPLES OF FRICTION HEAD LOSSES THROUGH SECTION ‘A’ WITH INCREASED FLOWRATES: A flow rate of 230 lpm through 38 mm diameter piping develops a friction head of 30 metres. A flow rate of 230 lpm through 50 mm diameter piping develops a friction head of 4 metres. A flow rate of 230 lpm through 75 mm diameter piping develops a friction head of 0.3 metres.



EQUIVALENT LENGTH OF FITTINGS

All fittings in the pipe-run including gate valves, 90-degree elbows, 45-degree elbows, Tee connectors and check valves contribute to friction head. Each twist or turn that the fuel has to take while travelling through the piping is treated as if the fuel had to travel that much farther through straight pipe. This resistance is shown as an equivalent pipe length for each type of fitting and should be added to the length of that section piping. Some examples of equivalent lengths are given below.

Equivalent Lengths of Pipe (metres)

Fitting Type 38 mm 50mm 90˚ Elbow 2.4 2.7 45˚ Elbow 0.9 1.2 Diversion Tee 2.7 3.3 Check valve 3.9 5.1 Coupling 0.3 0.6Gate Vave 0.25 0.4



PUMP SELECTION APPLICATION (from examples above)

TOTAL DYNAMIC HEAD at the shear valve is STATIC HEAD + DYNAMIC HEAD = 4 + 4 = 8 metres PIPE FITTINGS (eg) 6.3 metres PRESSURE REQUIRED AT THE SHEAR VALVE TO ENABLE DISPENSER TO DELIVER REQUIRED FLOWRATE (converted to equivalent friction head): DISPENSER MANUFACTURER’S SPECIFICATION = 1.4 bar (20 psi) = 20 metres TOTAL DYNAMIC HEAD INCLUDING FITTINGS AND DISPENSER HEAD =

8 + 6.3 + 20 = 34.3 METRES


Factors Affecting Pump Selection Overview DESIRED MAXIMUM FLOW RATE = 160 lpm. SYSTEM TOTAL DYNAMIC HEAD = 34.3 metres. Select the pump whose performance curve is bisected by the Flow Rate Curve closest to the Operating Point which in the example below is STP 1. Note: with this system’s TDH, if STP 2 is installed, the maximum flow rate would be 137 lpm

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0

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10 30 50 70 90 110 130 150 170 190 210 230 250Fuel Flow Required in LPM

Tota

l Dyn

amic

Hea

d in

met

res

STP 2

STP 3

Flow Rate Curve for the above Example Site

Pump Performance Curves

40

45

50

STP 1 Operating Point

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Factors Affecting Pump Selection Overview NOTE: TO REDUCE THE DYNAMIC HEAD AND THEREBY ENABLE A LOWER RATED STP TO BE SELECTED, THE FOLLOWING SHOULD BE CONSIDERED:

1. INCREASING THE PIPE DIAMETER IF PRACTICABLE. 2. REDUCE THE NUMBER OF ELBOW FITTINGS (USE FLEXIBLE PIPE WHERE

APPROPRIATE). 3. REDUCE THE NUMBER OF CONNECTORS AND VALVES.



FOR INFORMATION ONLY ACTUAL PERFORMANCE CURVES FOR RED JACKET STANDARD AND MANIFOLDED

STANDARD PUMPS

Red Jacket 50 HZ Standard Single Phase Pumps Performance Meters Head

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FLOW-PLM

TDH

-Met

ers

Standard 50 HZ P75U3 Manifolded Standard 50 HZ P75U3 Standard 50 HZ P150U3 Manifolded Standard 50 HZ P150U3

1

7

2

6543

14

12109

8

16

Number of Nozzles operating

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DYNAMIC HEAD:EXAMPLE:3 Dispensers - Number of nozzles = 6.Pipe diameter = 50 mm (2 inch)

DISPENSER MANUFACTURER’S SPECIFICATION = 1.4 bar TOTAL DYNAMIC HEAD INCLUDING FITTINGS AND DISPENSER HEAD =8 + 6.3 + 20 = 34.3 METRES

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