Hydraulics - System curve VS pump curve

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Discussion Overview

The discussion revolves around the relationship between pump curves and system curves in hydraulic systems. Participants explore the behavior of pumps in relation to flow and pressure, examining how these curves interact and what implications this has for system design and operation.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that as flow increases, the pressure generated by the pump decreases, questioning why this occurs given that pumps are part of the system.
  • Another participant suggests that increased flow makes it harder for the pump to generate the required pressure, indicating a potential misunderstanding of the system dynamics.
  • A participant proposes that when the system experiences too much pressure, the pump becomes overloaded, which may explain the observed behavior.
  • It is mentioned that a pump can only generate a certain amount of pressure, and beyond a certain flow rate, its maximum pressure output decreases.
  • A participant with practical experience explains that the pump adds energy to the fluid, contrasting this with the rest of the system, which only receives energy. They elaborate on how power is distributed between flow and pressure in pumps.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the relationship between pump and system behavior, with some agreeing on the principles while others raise questions or alternative interpretations. No consensus is reached on the underlying reasons for the observed phenomena.

Contextual Notes

Participants reference practical experiences and theoretical concepts, but there are indications of missing assumptions and potential misunderstandings regarding the dynamics of pressure and flow in hydraulic systems.

Femme_physics
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http://img849.imageshack.us/img849/9018/curvess.jpg

So pump curve, as flow increases, pressure drops. For the system curve, it's the other way around. How come? How come the pump disobeys the way the system is supposed to behave? The pump is a part of the system, and in the physical world, the more pressure there is, the better is the flow. I don't understand how come in the pump the more pressure there is, flow drops!
 
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Isn't it the other way around?
The more flow there is, the harder it is for the pump to generate the required pressure.
 
Ah...because there is too much pressure in the system, the pump is overloaded and its effect become less noticeable, right? Hmm... makes sense. So there has to be a relation between the pump and flow, and it's much easier to pick the correct pump than change the entire system to adjust itself to a pump. Brilliant. Thanks ILS!
 
Yep. A pump can generate a certain amount of pressure and when the flow rate increases, the maximum pressure it can generate, drops.
So the pump can not pump beyond a certain flow rate.
 
I like Serena said:
Yep. A pump can generate a certain amount of pressure and when the flow rate increases, the maximum pressure it can generate, drops.
So the pump can not pump beyond a certain flow rate.

Makes perfect sense, my sensei :approve:
 
I haven't had academic studies in such topics but as a result working with pumps and compressors for years, I have some practical understanding of such matters.

The main difference between the pumps and the rest of the system is that the pump gives energy to the fluid while the rest of the system only receive energy .In a pump the fluid flows from the lower pressure to the higher pressure which may be also surprising to you.

For a given power of the pomp, of course the higher pressure can be achieved for a lower flow ( the power is proportional to the product of the flow and the pressure difference of the pump ends). likewise, if we get a large flow from the pump, e.g by opening the discharge valve wider, the power of the pump is spent on a larger amount of the fluid, the fluid velocity and consequently the pressure would be less.
 
 
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