Increasing RPM's to gain flow 1

[mikecabs]

I understand that increasing the rpms will increase flow but how to know how many rpm's i can increase to before problems arise? My current motor is 10hp rated at 1770 rpm. Verticle turbine pump, 6 stages.

thanks

 

[ClicketyClack]

Depends on the pump design, system (NPSH in particular), motor limitations, etc.

Sometimes the system is the limiting factor, sometimes the pump design is the limiting factor, sometimes the motor...

We need more info.

 

[mikecabs]

don't have much info on the motor. for the pump, 8.9 ft. npsh is required.

 

[ClicketyClack]

You need to consider several things:

maximum stable flow for the pump
maximum RPM rating for the pump
maximum RPM rating for the motor
amount of flow where NPSHa < NPSHr
power of the motor vs RPM
intersection of system curve vs pump curve at varying RPM (keep it close to the BEP)
maximum pressure rating of system components
maximum inlet velocity of the pump
pump configuration (multiple turbines)
minimum submergence


One or more of these items will limit the max speed.

 

[Artisi]

First question is how are you going to change the speed of your 4 pole 60hz electric motor?

 

[mikecabs]

I am considering purchasing a new variable speed motor. Something that can operate at steady state 400gpm, and then for cold starts, around 600-800gpm. I guess I need to know if the pump can handle these new requirements.

 

[mikecabs]

I'm looking at my pump curve and where i want to be, 600-800 is too far off. my head would be really low and cavitation could occur. I think I might need to consider a new impellar. any sugestions would help.

 

[ClicketyClack]

There is more to it than that. I would call your local vertical turbine pump vendor.

 

[BigInch]

If lower rpm won't work due to high static head, its possible that changing impeller diameter won't work either and you will probably need a different pump in any case.

http://virtualpipeline.spaces.msn.com

 

[thewellguy]

The bowls, impellers and bearings should be fine, however I would be concerned about the H.P. rating of the drive shafts.

 

[Artisi]

without the pump curve in front of us we are all working in the dark. Can you post a copy of the curve so we can see what is going on and then give you meaningful suggestions.

The following link will allow you to post images.

http://www.freeimagehosting.net/

 

[ClicketyClack]

Even with just the fixed speed pump curve it's still a shot in the dark.

 

[BigInch]

Need the system curve too... and ...looks like a miner's hat.

http://virtualpipeline.spaces.msn.com

 

[mikecabs]

How in the heck do I post a file on this site? I tried copy and paste but doesn't work...

 

[mikecabs]

here is the link for the pump curve

 

[BigInch]

And the system curve?

========================================================
I post the images I want to show on

http://www.eng-tips.com

to an image hosting website called Image Shack. There are a number of free hosting sites on the net, but you can find Image Shack at,

http://www.imageshack.us

Go to

http://www.imageshack.com

and find the instructions for uploading an image to their servers. It typically just amounts to browsing your computer for your diagram and clicking the ImageShack button to upload the diagram.

Once the diagram is transferred to Image Shack, their web page will return several examples showing a number of common ways to link your uploaded image to various classes of web sites. Find the example link that looks like this one,



Unfortunately that does NOT work on Eng-Tips as it is, so you have to edit that link.

You should edit your link by removing all the characters indicated by "^" in the following,


[url htp://imageshack.us]
^^^^^^^^^^^^^^^^^^^^^^^^^

[/url]
^ ^^^^^^

leave a space where the equal “=” sign is.

You should now have a link that looks something like this,

Copy and paste that link where you want your diagram to appear in your eng-tips posting.

After you have the link pasted into eng-tips and finished your question or comment, check your work for proper formatting by clicking the "Preview Post" button just below the text box.

If it looks good, click "Submit Post"
=========================================================

http://virtualpipeline.spaces.msn.com

 

[ClicketyClack]

Can we start a forum on image posting If it's not made of metal I'm really not sure what I'm supposed to do with it.

 

[BigInch]

If you can make an image, follow the above instructions to post it.

http://virtualpipeline.spaces.msn.com