8 replies to this topic

[ethanhan]

Hi to all experts


I would like to know does liquid with different density is applicable to same centrifugal pump curve? Let say, if 2 different liquids with different density will have same shut off head for a identical pump?

Thanks
Ethanhan

[mishra.anand72@gmail.com]

May be same shut off head . However discharge pressure will not be the same.

[msam]

May be same shut off head . However discharge pressure will not be the same.

Hi all,

I have joined this forum only today.
Nice to meet you all friends.

Well, regarding this issue, for a specific pump the head in terms of metre liq., will be the same for all liquids, but discharge pressure will vary from fluid to fluid, as it is proportional to the density.

[Zauberberg]

The term "head" is used in design and operation of centrifugal pumps in order to avoid confusion with different pressure values. Suction head, differential head, shut-off head - these are all parameters independent of fluid specific gravity and, in any time, you can convert value of head to corresponding pressure.

If pump NPSHR is 2m, it means that the height of liquid required for regular pump operation is equal to net positive head of 2m. This also means that suction pressure will be different for various liquids, but the head is always the same.

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http://www.mcnallyin...aper_index.html

Best regards,

[Art Montemayor]

Zauberberg has hit the nail on the head with his concise response and with his recommendation.

There is a distinct advantage to measuing the energy of a pump as "head" instead of "pressure". The head applies to any liquid that is pumped at the same rated capacity and speed, as long as the viscosity is low (generally less than 10 cP). The head produced by a pump will remain constant (at a defined speed and flow rate), even though the pressure differenctial and power requirements may vary.

Pumped fluid properties have a significatnt impact on the head. In particular, as density and viscosity increase, so will the amount of work needed to drive the pump. This is the reason why process engineers must specify not only the normal values for density and viscosity, but also the maximum values that the pump is likely to encounter during extreme operational situations - such as startup, shutdown or process upsets ("excursions").

[fallah]

I think in a specific pump and its pump-curve, for various liquids (different in density), as long as viscosity is low, we can consider the same curve and the same working-point for constant capacity, but the power increases with increasing density.Please correct me if i am wrong.

Regards

[ethanhan]

Hi to all


Yes I agree with you all. But according to the concept of pressure, especially at the shut off head, the maximum pressure the pump can be provided should be same for different fluid density? Thus it lead to shifting of pump curve?

Example:
I have a pump which pumping liquid with S.G 0.6 previously. Now, I would like to change a liquid with S.G 1.1. And both mentioned liquid have approximate viscocity. The elevation, pump, motor, system curve are still remain same. Thus do the shut-off head remain same? Do the pump curve have shifted? The pump curve is still applicabe since fluid density is different?

Thanks
Ethanhan

[Zauberberg]

Ethanhan,

I think you should read our replies more carefuly. Everything you need is already written above. And more than that.

Best regards,

[Mahesh@A&M]

Ethan,

If you are pump water ( S.G =1) at a rate od 1200 lb/hr and now you want to change pumping liquid with S.G of 0.8, you will get 960 lb/hr.

Head generated by the pump will be same for any type of liquid. With changes in spcific gravity, your pump differential pressure will change. Pump manufacturers use cold water to generate pump curves. so volumetric flow rate, differential head and pump efficiency are independent of liquid pumped. NPSH r will be worst for cold water and hence values published on the curve are safe for any liquids.

Now that u want pump liquid with S.G of 1.2, your power reuired to drive the pump i.e, hydraulic power will increase. Pump curves are standard for nay type liquids being pumped. As u can see from my above comment, your flow rate will decrease and DP will change and hence your operating point.

Jedi's, correct me if I stated wrong with an year of experience. Chemical Engineering is my passion and I read most of the threads in this forum and Eng-tips to educate myself to next level.

Thank You
Roopa@Aggie06