Understanding the Up-Left Quadrant of Pump Function: Q>0 and n<0

[Mikealvarado100]

Hi
Could anyone describe each quadrant (of four quadrants) of pump function which includes combination of Q (fluid) & N (rotation) duration transient analysis? (second quadrant especially which Q>0 and n<0)

 

[Mikealvarado100]

 

[Nidum]

The diagram just illustrates the four possible operating modes of a CF pump .

In quadrant 2 back pressure is higher than the pressure that the pump can generate so fluid is flowing backwards through the pump .

Visualise the pump delivery being directly connected to the bottom of a large tank .

Pump has to overcome static head at base of tank before any fluid can be pumped into the tank .

If pump cannot overcome the static head then fluid will flow out from the tank , downwards through the pump
and back to the fluid source . Rotation of the pump may inhibit this back flow somewhat but more likely the pump will just cavitate and churn water uselessly .

 

[Nidum]

I don't see how the diagram helps with understanding of transient effects in pumps very much though .

What exactly are you trying to find out ?

 

[Mikealvarado100]

Nidum
1- Thank you very much, but I still can not comprehend how pump can rotate agaist the flow direction? I mean that when flow direction is inverted, pump's rotation HAVE TO change. What do you think?
2- Let me use this opportunity to ask another question: Why H=0 in two first quadrants and H>0 in quadrant 3&4? What does H mean in this issue?

 

[jbriggs444]

Nidum
1- Thank you very much, but I still can not comprehend how pump can rotate agaist the flow direction? I mean that when flow direction is inverted, pump's rotation HAVE TO change. What do you think?

There is nothing that stops you from forcing water against the direction the pump is pushing. For a piston pump, this would force the shaft to rotate backwards. But for a centrifugal pump, the shaft can continue to turn forward while fluid is forced back through the vanes.

 

[Mikealvarado100]

Nidum
And about H?

 

[Mikealvarado100]

Hi everyone

Regarding this page (https://www.physicsforums.com/threads/four-quadrants-of-pumps.875380/#post-5499831), I am trying to describe 4-quadrants of a pump (CF exactly) while transient event occurs as the photo shows. Then please let me know whether my thought is correct or needs to modify to be correct:

Quadrant A): Up-Right: In this quadrant Pump acts normal behavior. Pressure of wave right next to the (discharge side of) pump is NOT higher that Pump’s generated Head and it results flow from suction side to discharge side of pump.

Quadrant B): Right-Down: In this quadrant a increased wave reaches from downstream to the pump and pump’s head can not overcome this strong wave. Then what happens is reversing flow direction (from discharge to suction side) while vanes’ direction do not change. If this situation continues, then vanes stop and reverse gradually which enter quadrant C:

Quadrant C): Left-Down: In this case, both flow direction and rotation direction have been changed and pump behaves like a turbine. Vanes transfer fluid from discharge side to suction side of the pump.

Quadrant D): Up-Left: A decreased wave reaches the (discharge of ) the pump and pump can overcome it. Then the pump transfer fluid from suction side to discharge side of it, in spite of not reversing vanes’ direction. If this situation continues, the vanes stop and it’s direction changes gradually and back to Quadrant A).

Please remark my explanation and let me know your idea.

Thank you very much.
http://s6.uplod.ir/i/00788/maa0dogf9fh8.jpg Hi

 

[256bits]

Nidum
And about H?

H is the head at the pump exit.

One can also have a line of zero torque, T=0.

http://authors.library.caltech.edu/...e in the Prediction of Transient Behavior.pdf ( 1937 )
It gives some discussion, plots, testing setup.

If you look at Fig 6 on page 685 ( PDF Page 3 ), a graph of the pump 4 quadrient characteristics, and some labeling of zones.
That may help you out.
( You should note that the quadrients are labeled a bit different than you diagram ( 3 and 4 ), so be sure to first check that out in any literature you find.

Your transient explanation seems to make sense.
But then again, these diagrams are difficult at the best of times.
Most engineers are usually interested in the pump normal flow characteristics.
I guess in your case for pipeline flow, they become more important to see where a pump would be operating, under certain conditions.

 

[Mikealvarado100]

OK, I will read the paper soon. But is my explanation correct or not?

 

[Nidum]

(1) What actually happens will depend on the nature of the pressure transient , the characteristics of the pump , the characteristics of the motor/engine driving the pump and the responses of any control and safety systems .

(2) 'Wave arriving' is too loose a definition for a pressure transient .

Some possible cases of pressure transients on the delivery side of a pump are :

(a) A gradual change in pressure .

(b) A step change in pressure .

(c) A pressure pulse .

Response of a given installation of a pump will be different for each case .

Transients are not always simple and easy to define . They can be complex continually varying events lasting long periods of time .

(3) Different designs of pump will respond to transients in different ways .

(4) The motor/engine may be able to sustain constant forward speed under all conditions or it's speed may vary with load .

(5) In reality control and safety systems would usually shut the pump installation down in the event of reverse flow or other malfunction .

 

[Mikealvarado100]

Nidum
The issue made me a little bit confused.
Would you explain four quadrants of pump reaction (while transient event occurs) separately.

 

[Nidum]

(2) 'Wave arriving' is too loose a definition for a pressure transient .

Please tell me what you actually mean by 'wave arriving' .

Please also tell me why you are interested in this problem and what your technical background is ,

 

[Mikealvarado100]

The diagram just illustrates the four possible operating modes of a CF pump .

In quadrant 2 back pressure is higher than the pressure that the pump can generate so fluid is flowing backwards through the pump .

Visualise the pump delivery being directly connected to the bottom of a large tank .

Pump has to overcome static head at base of tank before any fluid can be pumped into the tank .

If pump cannot overcome the static head then fluid will flow out from the tank , downwards through the pump
and back to the fluid source . Rotation of the pump may inhibit this back flow somewhat but more likely the pump will just cavitate and churn water uselessly .

Nidum
I think you are explaining the quadrant 4 (right-Down). I asked about Up-Left Quadrant.