Specific Gravity impact on the system Curve
Specific Gravity impact on the system Curve
(OP)
Hi,
I am running calculations to build a system curve for a pump. From what I understand the S.G. of the liquid being pumped has no impact on the head loss in the system. As long as the pump can provide enough head, I should be able to push the water out at a certain flow rate (intersection of pump and system curve point). I will obviously take into account the increased HP required.
BUT, I've come across differing calculations.
Flygt slurry pump handbook states you have to use a friction loss correction factor to calculate the head loss when using SG not equal to 1.
On the other hand, other online friction loss calculators (Goulds Pump selector) give the same head loss whether I use SG 1 or SG 1.5.
Could someone clarify this please. And if we do use a correction factor, link to a table. Thank you so much in advance.
I am running calculations to build a system curve for a pump. From what I understand the S.G. of the liquid being pumped has no impact on the head loss in the system. As long as the pump can provide enough head, I should be able to push the water out at a certain flow rate (intersection of pump and system curve point). I will obviously take into account the increased HP required.
BUT, I've come across differing calculations.
Flygt slurry pump handbook states you have to use a friction loss correction factor to calculate the head loss when using SG not equal to 1.
On the other hand, other online friction loss calculators (Goulds Pump selector) give the same head loss whether I use SG 1 or SG 1.5.
Could someone clarify this please. And if we do use a correction factor, link to a table. Thank you so much in advance.





RE: Specific Gravity impact on the system Curve
I've removed my original post. I'll put more thought into it next time. Sorry for presenting incorrect info.
RE: Specific Gravity impact on the system Curve
Suggest you read the following, plus there is unlimited info on the net regarding this subject.
http://www.pumped101.com/sgviscositypart1.pdf
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: Specific Gravity impact on the system Curve
Most other systems can't and if the viscosity remains the same then the pressure drop (system curve) will remain the same. This is quite unusual and therefore when the SG changes so does the viscosity.
As SG rises, then so does the pressure for the same head. Pump power also rises in proportion.
someguy79 - I don't believe your first para is correct. Static head is static head, usually a physical thing -height of a hill or end point e.g.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Specific Gravity impact on the system Curve
RE: Specific Gravity impact on the system Curve
SG, solids concentration, shape- size and grading of the solids (uniformly mixed sizes, all one size), SG of the solids, etc. For true slurry handling applications care needs to be taken along with careful analysis of the effect it will have on the pump performance.
Weir pumps (Warman slurry selection data)and GIW have good selection information available.
Flygt and like companies are usually only interested in sewage or similar light and easily pumped "slurries".
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: Specific Gravity impact on the system Curve
NO it doesn't,
see https://en.wikipedia.org/wiki/Darcy%E2%80%93Weisba...
The equation where density comes into it is PRESSURE loss, not head loss.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Specific Gravity impact on the system Curve
as seen here on Wiki,
https://en.wikipedia.org/wiki/Darcy%E2%80%93Weisba...
That equation does show that PRESSURE LOSS per unit length of pipe DUE TO FRICTION is proportional to the SG of the fluid, however for HEAD LOSS that is NOT SO. Head loss is different than pressure loss because it is independent of SG.
This DW equation,
as seen farther down on the same Wiki page, clearly shows that HEAD loss due to friction is actually independent of SG.
Head loss due to friction only depends on viscosity only. Pressure loss is simply a derived unit of the hydraulic head loss process used by those engineers that for some reason prefer more complexity and want to introduce specific gravity into the equation so that they can speak in terms of pressure loss. Frictional Head loss for all fluids with the same viscosity is the same, regardless of their SGs, however different SGs will cause those equal head losses to show different pressure losses.
RE: Specific Gravity impact on the system Curve
RE: Specific Gravity impact on the system Curve
Reason why I ask this is our supplier, uses head loss through pipelines for slurry = head loss through pipeline for clean water * SG
I always questioned that and wanted to get concrete evidence before going back to the supplier.
http://www.pumpfundamentals.com/slurry/flygt_slurr...
Page 42-43 confuses me, because even though flygt isn't in the proper slurry market they their handbook is using a correction factor to calculate head loss for slurry.
I'll read through the weir handbook and update
RE: Specific Gravity impact on the system Curve
We are simply stating that the true parameter on which to base fluid frictional losses is viscosity and that theoretically IN THE GENERAL SENSE there is no theoretical relationship between specific gravity and frictional loss, nor is any necessary to determine head loss. That's not to say that a relationship between specific gravity and viscosity can not be found, or does not exist in what probably is a very large number of fluids.