VERTICAL TURBINE CENTRIFUGAL PUMP IMPELLER DESIGN

[SShiva]

We are going to install a vertical turbine type centifugal pump with three stages. It is going to pump process effluents to the sea from an holding basin. One manufacturer has offered radial vane type impeller and other with a diffuser. Vendor with the diffuser claims diffuser type impeller supplied has got seven vanes and eight cases and that shaft deflection is minimised and claims superiority over the radial type. I would like to have more understanding on the above for proper selection.

Suction specific speed offered for the radial type is 8640 (US units). Is it ok for this type of pump

 

[Aleksandar]

For specific speed 8640 (if this is specific speed for one stage)you have to go with mix flow impeller. Mix flow impeller will give in the end smaller pump diameter whic can reduce cost of bore.

 

[npsingh]

Anyone please suggest me some sources for pump casing and impeller design? N P Singh

 

[tstead]

Call the manufacturer on their claim. Tell them to back up their claims and provide you with shaft defelction claculations for both designs.

If they can't provide you with shaft defelctions on both designs then how do they know that theirs will have less?

Since they cannot provide you with the calcs on their competitor's pump, ask them to provide just theirs. Then, go to your competitor and as that they provide you with the same.

Compare numbers. That is the only way to really know.

*DISCLAIMER: This next paragraph is harsh and discloses my disgust for salesmen*

I have to say that initially, I would say that their claim is total BS and is nothing more than a sordid excuse to buy their pump. That is a salesman talking out of his rear and blabbing about something which he has little to know knowledge about. After all, if they had any proof that their pumps had lower deflections then they would have given you numbers not excuses.

I'd tell the guy to shove it and that you'll but your pump from someone who won't give you a fancy "pick-up line" to sell a pump.

 

[vinayakb50]

Choice of radial or mixed flow impellers depends on the specific speed (ns = n * Q**0.5/ H**0.75) of pump stage. Upto about 1500 rpm(USGPM based) specific speed radial impeller design is the best and we should go for mixed flow impeller for specific speed (USGPM based) from 1500 rpm to 8000 rpm.

Pumps whether with radial or mixed flow impellers can be provided with volute casings or diffusers. It is true that pumps with diffuser casings will experience considerably lower radial thrust than with volute casings and such their shaft deflection will be lower.

You have not mentioned if radial pump is provided with diffuser or volute casing. This will determine whether it will have larger shaft deflection than mixed flow impeller pump with diffuser.

Yes, the suction specific speed of 8640 rpm(USGPM based) seems to be OK for radial vane impeller pumps.

 

[DeltaCascade]

Tstead, that "disclaimer" was pretty harsh. Tx to vinayakb50 for shedding light.
Buyer beware, yes, but not malicious.