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minimum safe flow centrifugal pump

Attached to accompany blog entry entitled:

Minimum Safe Flow for a Centrifugal Pump

Good Ankur,

Please, how can one determine the pump efficiency at shut-off for a pump when the efficiency at zero flow and shut-off is zero when read on the pump performance curve.
vamsi
sir,
miminum safe flow flow for centrfugal pump apart from temperature rise,
do we need specify minimum safe flow based on mechanical vibrations(safe limit) of rotating equipment ?
venkisowji
Dear Ankur,

Good Day...Its a very good blog and thanks for sharing the same.

Regards,

VENKI.
ayush

Sir,

ankur2061

Sir,

Ayush,

Your statement is incorrect. The pump efficiency will be low but it cannot be zero. The pump is still running against a blocked discharge and the mechanical energy from the driver of the pump is being lost by generating heat in the pump casing instead of overcoming the head as change in the potential energy of the liquid being pumped

This can be proven through the power equation for any pump:

P = Q*H*ρ*g / 3600*η*1000

where:

P = power, kW
Q = volumetric flow rate, m3/h
ρ = density, kg/m3
g = 9.81 m/s2 (grav. constant)
η = efficiency, %

If η becomes zero the power required at shut-off would be infinity which is not correct. Hope it is clear now that efficiency is not zero at shut-off.

Regards,
Ankur.

PRkumar

DEAR SIR,

THANKS A LOT FOR WRITE THIS BLOG & ATTACHED THE DATA SHEET.

ayush

Thanks alot sir for clarifying the doubt.

Sharma Varun

Sir, its a great blog, thanks for the reference also.

Please recheck the temperature unit conversion.

Sharma Varun

Sorry @ the last query sir I got the temp. conversion.

However going through the formula, t = (1-e)*Hs/778e

here what is significance of 778, I am asking this because I am confused wether this equation is valid for any liquid or only water?

Sharma Varun

You can not generalise the equation it is for water only, one needs to use it w.r.t pumping fluid specific heat.

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