7 replies to this topic

[Sridhar P]

While selecting a pump from vendors, for same duty different vendors are providing pumps with 1500 rpm and 3000 rpm. What are the positives and negatives for those rpms. Which pump should be selected.

Regards,
P.Sridhar

[djack77494]

Which pump should be selected.

I can't answer that question but can say that there are some advantages and disadvantages to both (i.e. high speed and low speed) approaches. You will obtain a physically smaller and probably cheaper pump using the higher rpm driver. You will pay for that in a higher NPSH requirement and a greater likelihood of maintenance problems. Before I hear too many complaints about this response, let me say that I know this is very simplistic. I am basing these statements on higher speed = tighter tolerances needed, greater relative velocities of moving parts, etc. These factors tend towards increased maintenance requirements, but can be mitigated (at a cost) with better quality manufacturing. Best to look at the multiple offerings, compare pump curves, etc. and talk to the manufacturers to see what they have to say. Some companies also have requirements for such factors as specific speeds that maybe could be met with the lower but not the higher speed pump. I can't offer you any more than gross generalizations at the point.

[Andrei]

Sridhar,

I am using the term "duty" when discussing about heat exchangers, for pumps I usually use characteristics, or capacity, or head. And I think a lot of others are doing the same like me.
For the same characteristics, during my plant operating experience, I always preferred low speed pumps. Lower maintenance costs and more reliable overall. The pumps I was operating were handling fluids prone to cavitation: very high dissolved gas content, close to boiling point operation, liquefied gases, high volatility liquids. So, using low speed pumps was imperative. Generally I would expect a 3000rpm pump to fail quicker than a 1500rpm one. I remember some 1500rpm pumps that almost I didn't know that were there, no problem at all for several years. But I remember 3000rpm pumps that gave me headaches almost daily.

[Qalander (Chem)]

Sridhar,

I am using the term "duty" when discussing about heat exchangers, for pumps I usually use characteristics, or capacity, or head. And I think a lot of others are doing the same like me.
For the same characteristics, during my plant operating experience, I always preferred low speed pumps. Lower maintenance costs and more reliable overall. The pumps I was operating were handling fluids prone to cavitation: very high dissolved gas content, close to boiling point operation, liquefied gases, high volatility liquids. So, using low speed pumps was imperative. Generally I would expect a 3000rpm pump to fail quicker than a 1500rpm one. I remember some 1500rpm pumps that almost I didn't know that were there, no problem at all for several years. But I remember 3000rpm pumps that gave me headaches almost daily.

Sridhar, Hello/Good Morning,
I believe a more appropriate word is 'service' for pumps comparable to 'duty' for heat exchangers case.
Regards
Qalander

[joesteam]

An issue that my customers are concerned about is noise, not just in the pump but also throughout the piping. Lower speed = lower noise.
However, some combinations of flow and head suit themselves to higher RPM pumps. These are (generally) lower flow and higher head, where you will be working much more efficiently on the pump curve with a higher RPM motor.

[Technocrat]

Dear Sridhar,

Please also consider size of pump and motor to suit available plot space. Also check electrical maintenance cost for different rpm.

Regards.

[empower70]

Dear Sridhar,

Please also consider size of pump and motor to suit available plot space. Also check electrical maintenance cost for different rpm.

Regards.

Gentlemen,
I would like to add one more point, that higher rpm pump is having higher energy density; which causes increse in vibration, so bearing selection shall be carried out accordingly.Refer API 610 10th edition, table 9.

Regards,

empower70

[Lukman]

First you should calculate whether motor speed at 1500 rpm is enough or not. If it fits with your process requirement, then you must refuse 3000 rpm pump. Because you will utilize unnecessary electric power than for your requirement.
Of course you will also pay higher cost for 3000 rpm pump as well as higher capital and manitenance cost.