VENDOR TO ADD MINIMUM CONTINUOUS REQUIRED, 30% ??

[martinpump]

Hi All,

In the data sheet, RATED USGPM is 2140. No NORMAL USGPM is specified.
And a note is given

MINIMUM FLOW PROTECTION WILL BE USED. PUMP VENDOR TO ADD MINIMUM CONTINUOUS REQUIRED FLOW
TO RATED PUMP CAPACITY. TURNDOWN SHALL BE MINIMUM 30%.

So do i need to add 30% extra to 2140 GPM ie 30% of 2140 is 642.
Does it mean my total design capacity is 2782?

Thxs

 

[LittleInch]

It does read like that.

The only thing I can think is that the system it is going into has a recirculation loop continuously open regardless of flow and hence to get 2140 out of the pump final discharge, your pump is actually pumping 2140 + 30%. Very wasteful of energy, but possible.

Sounds like you need to ask them a question....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[martinpump]

Yes as per client the flow will be reverted back, my question is how much do i need to add to 2140.
Is the calculation of mine correct ie 2140 x 30% = 642
So 2140+642=2782

Or

2140/0.7=3057?

Really confused.

 

[LittleInch]

I believe your first calculation is correct (2782) , but I would confirm with the client.

Of course you also need to make sure your pumps minimum continuous flow needed is <= 30% of the rated flow otherwise you would need to add a different figure....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TenPenny]

Here's how I interpret this:

You need to add whatever your minimum flow is to the 2140; once you've picked your pump, you will know what the min flow is, we don't know what pumps you sell.

I believe they are asking for the min flow to be less than 70% of the total you get from above, which seems like that won't be an issue.

 

[martinpump]

Thanks All,

Well do u have any Vertical pump minimum submergence level calculation books
i was informed that GOULDS have a very informative book for this, can i have a copy if available please.

 

[TenPenny]

Not sure what book you would be referring to, but here is the chart on minimum submergence. It's actually a Hydraulic Institute document.

 

[martinpump]

Thanks TenPenny
However i need formula book to calculate the vertical pump levels

 

[Artisi]

Submergence levels would be readily available on the internet if you took the time to research it. Or purchase a good pump book.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Loifer]

Welcome everyone!
I'm new in here, I work with pumps for a few years, pump sump huoses etc. (power stations cooling system design).
Talking about minimum submergence:
well the manufacturer has to tell you his pump's minmum submergence required
other issues are in the S parameter of submergence are: NPSHa that you have and NPSHr you want (NPSHa margin from cavitation). After you demanded min. of NPSHr the manufacturer would know which pump to offer you depending on the flow capacity and TDH you required.
hope it helped.

p.s

In pump sump there is also the minimum depth parameter S, and C the distance from bell suction to bottom - See ANSI/SI - pump standard (Hydraulic Institute)
(S-C= minimum submergence of the bell)

 

[DubMac]

Extremely confusing way that the rated flow specs are written indicates the writer is confused or made a mistake. I would ask for clarification and fast! Don't pretend to know or guess what that statement means. I agree with Tenpenny: add pump's MCSF to the rated flow. The statement after that doesn't make sense. Could he mean Max turndown is 30%?

Also remember that only one rated point is guaranteed; not two points or a range of flow.

Minimum submergence is not related to NPSH issue; it is related to the vortexing ability of the pump. Minimum submergence values can be had from the bowl manufacturer; they are also dependent upon the design of suction bell/case, and also the pit design. There should also be a value for how far off bottom the pump must be set. You can do all the calculations you want and still get it wrong if not empirically tested. Take advice from the manufacturer on this; they've done testing.

 

[martinpump]

Well Thanks All, now its clear.
The client advice me to first select the nearest pump, then what ever the BEP flow is take 30% of that and add it to rated Q.

Its now clear.

Thanking you all.

further to this what is this attached picture.

what is it used for?

 

[1gibson]

Be careful. If you change the: rpm, head, impeller diameter, then you will have to revise the flow a small amount to compensate. The rated conditions appear on almost every document, these will also need to be revised. The client might ask for these revisions for "as-built" test data, and then you are in trouble. Make sure everyone is on the same page that the conditions are per the datasheet and are locked in as numbers, not relationships, at the start of the project. Strike the note on the datasheet and replace it with actual numbers during the first revision.

Picture is a CMM arm, it gives you a complete readout of the geometry of a part. Dimensions, parallel, concentricity, etc. Results are only as good as the operator, so take with a grain of salt and check these on a turntable or a machine if possible.

 

[Pumpsonly]

Your client need some education on pump operation. To add 30% to the rated flow for such a big pump is a waste of 30% extra energy
necessary to do the job. It means 642 gpm of water is being dump back to the suction. You can check it easily with the require motor power at 2140 gpm and 2782 gpm. Further more if you selected the pump based on 2140 gpm at near BEP, the pump curve may not extend beyond another 30%. You also have higher NPSHR and submergence beyond the BEP.

If the selected pump can not be operated below the minimum process flow required, it is much better to have a by-pass line that only open when the process flow is lower than the pump minimum flow.