Chemical Technology April 2016

from the slurry supply surface level to the

centre line of the pump m.

= Head loss of inlet in metres of slurry

= Loss of head inmetres of slurry in the suction pipe

atm

= at 3 100 m above sea level, pressure is 6,1 m

of water =6,1/1,14 = 5,4 m slurry

vap

=2,19 ft water is 0,67 m water at ambient

temperature which is 0,67/1,14 = 0,59m of slurry

= 5 m

=0,5 x v

/2 g = 0,5 x 2,2^2/2 x 9,81 = 0,12 m

of slurry

=8,4 m of slurry

NPSH

= 5,4 – 1,92 - 5 – 0,12 – 8,4 = - 10 m

which is seriously negative, so there is no

suction head available to allow pumping to

take place.

If the pump was at sea level then the equation would be

as below:

NPSH

= 11,9 – 1,92 - 5 – 0,12 – 8,4 = - 3,54 m , even

at sea level there is not sufficient available

NPSH.

NPSH

= this can be read off the pump curve and is

always positive.

So operating at sea level will not make any difference to the

available NPSH as calculated above.

Since the operation is at 3 100 m above sea level, a reduc-

tion in the suction height to 1 m will make

NPSH

=5,4 – 1,92 - 1 – 0,12 – 8,4 = - 6 m which is still

less than the NPSHr and cavitation will occur.

Chemical Technology • April 2016

Conclusions

As we can see from the calculations, we have an inherent

problem with the head loss in the suction line. The suction

line loss of 8,4 m is far too large and has to be reduced

to about 1,5 m. To do this we can increase the size of the

suction hoses, but this may dredge far too large an amount

of water and gravel to handle.

The Diamond River Hunters then decided to dig the

diamondiferous gravel out of the stream with a front end

loader and to dump the material into a hopper from where

it was sluiced into the ‘trommel’. The small pump necessary

to raise clean water to the hopper is achievable.

The Klondike Gold miners use this technique, but the

earthmoving equipment is forever breaking down and spares

are hard to come by.

The moral of the story, for us all to note, is to spend far

more time planning a venture and designing the infrastruc-

ture before heading out on site where rectifying engineering

problems is far more difficult than being able to redesign on

a computer in the office!

References

2 The hydraulic Transport of Coal and Solid Materials in Pipes –

R. Durand, E. Condolios –LaboratoireDauphinois d’Hydraulique, 1952

3 Durand, R. (1953). Basic relationships of the transportation of

solids in pipes - experimental research. Proc. Minnesota Interna-

tional Hydraulics Convention, Minneapolis, Minnesota, pp. 89-103

4 Slurry Transport using Centrifugal Pumps – K.C. Wilson, G.R. Ad-

die, A. Sellgren, R. Clift – Blackie Academic & Professional, 1996

5 Slurry Pump Handbook – 2009, Fifth Edition, Electronic Version,

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