SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
(OP)
Dear guys,
A recent project was undertaken and I was asked to review the design of the pumping system and determine if it was appropriate or not. I determined the various parameters and came up with a graphical representation of the system resistance curve superimposed on the curve of the pump that was selected for that project. I have attached the file here. It is obvious that the pump curve does not intersect the system resistance and thus the design was not done appropriately. Nonetheless practically, the pump works! Can I get a thorough analysis from any of you pump experts? What is actually happening? Why is the pump working in reality?
A recent project was undertaken and I was asked to review the design of the pumping system and determine if it was appropriate or not. I determined the various parameters and came up with a graphical representation of the system resistance curve superimposed on the curve of the pump that was selected for that project. I have attached the file here. It is obvious that the pump curve does not intersect the system resistance and thus the design was not done appropriately. Nonetheless practically, the pump works! Can I get a thorough analysis from any of you pump experts? What is actually happening? Why is the pump working in reality?





RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
You need to show us the REAL pump curve not some graphic representation, showing the full H-Q curve, power curve, NPSHr together with the site conditions including NPSHa etc.
The two line plot is next to useless for anything meaningful.
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: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
One easy way to see what is happening to your pump is to go check the amps it is consuming. Nearly all switch boards show this or record it as a standard feature so you don't need to go and fix any new instruments.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
Technically, if the pump works, then the pump curve MUST intersect the system curve, because the point where you are operating is the intersection of those two curves.
In order to give any meaningful analysis, you'd need to supply at the very least the actual pump curve, and also verify operating speed as compared to the speed shown on the pump curve.
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
I hate Windows 8!!!!
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
No, you're right, they only have to intersect in order for the pump to do anything.
As long as you're happy for the pump to not actually do anything at all, they don't need to intersect.
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
Your highest tank level is 21m with a full tank and the loading arm is 3m, and you say that you reduce the head with a lower tank level. That makes no sense to me, if the tank level is lower, the static head should be higher.
Also, for clarity, your switching of units between the sulzer curve and your spreadsheet definitely makes it more confusing.
But I'm baffled by your static head / tank level comments, I must be missing something.
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
Therefore your curves seem incorrect as the head at 0 is shown as nearly 20m. This doesn't match your data. However with 18 loading Bays, how many have you assumed on. I assume your pumps all work in parallel. I'm taking a guess here that your loading Bays actually have a valve or other device which restricts Max flow to a certain level. On a head chart this is repeated by a vertical line.
The static head at zero flow is the head you need to reach to get flow, e.g. you have an empty tank 15 m higher than your pump, then until you get a head of 15m you won't get any flow. This doesn't look like your system, but only you know and we've got about 10% of the information you have, but you seem to expect us to guess it all....
Your system sounds much more complex than a simple chart as you've drawn it, though I'm puzzled by your x axis. You shows about 65m3/hr as the end curve point, but the pump curve is nearly 240. What's going on?
I think you need to post your system diagram and your excel sheet if we're going to be able to see where you seem to be going wrong.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
Davincigee, please give us the full picture about what you're trying to do and what you're system is and how it works.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: SYSTEM RESISTANCE CURVE NOT INTERSECTING PUMP CURVE
Seems a major cock-up somewhere and the pumps are way oversized.
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.)