Minimum Flow using Suction Specific Speed
Minimum Flow using Suction Specific Speed
(OP)
Hi Guys,
I am new here and just been looking to find some guidelines to have a consevative minimum flow for pumps. I came across this thread http://www.eng-tips.com/viewthread.cfm?qid=278130 and there is a table by JJPellin
What are the units used for in calculating Suction Specific Speed and Specific Speed?
Do you use NPSHR for water or do you determine the NPSHR for the liquid that is being pumped?
Thank you.
P.S I am having relibility issues operating a turbine driven pump in parallel to an electric motor driven pump with both operating simultaneously. Its quite similar to this thread http://www.eng-tips.com/viewthread.cfm?qid=337412
I am new here and just been looking to find some guidelines to have a consevative minimum flow for pumps. I came across this thread http://www.eng-tips.com/viewthread.cfm?qid=278130 and there is a table by JJPellin
which uses Suction Specific Speed and Specific Speed to define the minimum flow at percentage of BEP. So I have two questions in particular:Quote (JJPellin)
What are the units used for in calculating Suction Specific Speed and Specific Speed?
Do you use NPSHR for water or do you determine the NPSHR for the liquid that is being pumped?
Thank you.
P.S I am having relibility issues operating a turbine driven pump in parallel to an electric motor driven pump with both operating simultaneously. Its quite similar to this thread http://www.eng-tips.com/viewthread.cfm?qid=337412





RE: Minimum Flow using Suction Specific Speed
You can use any unit of flow, but the number you get must correspond to whatever scale you are using to gauge your pump's performance. If you use USGPM, the scale is already a standard.
you must get smarter than the software you're using.
RE: Minimum Flow using Suction Specific Speed
RE: Minimum Flow using Suction Specific Speed
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.)
RE: Minimum Flow using Suction Specific Speed
RE: Minimum Flow using Suction Specific Speed
I think they are good for the specific speed ranges stated.
I think they are rather too conservative for the suction specific speed ranges used. Particularly at low combinations of low specific speed and high suction specific speed, they are significantly off of the mark. The other missing component is running speed which has a significant effect.
A couple of papers that might be of interest as to where we've been (in the 1980's) vs. 2014 are linked to below.
https://docs.google.com/file/d/0BxB_abOe1xD7cjZ1bl...
http://turbolab.tamu.edu/proc/pumpproc/P29/Lecture...
RE: Minimum Flow using Suction Specific Speed
Yes, you're absolutely right. I had a look at the graph and it is a bit less conservative.
I am new to pumps and the pumps I have been looking at have almost double the MTBF as others. The pumps have suction specific speed of 17050 (USGPM and ft) which is quite high. They are being operated at 75% flow rate of BEP. So no wonder there are more issues with these pumps.
Thanks a lot, I will have a read through the papers and explore the subject a bit more.
RE: Minimum Flow using Suction Specific Speed
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.)