# Hydraulics - System curve VS pump curve

1. Feb 26, 2012

### Femme_physics

http://img849.imageshack.us/img849/9018/curvess.jpg [Broken]

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!

Last edited by a moderator: May 5, 2017
2. Feb 26, 2012

### I like Serena

Isn't it the other way around?
The more flow there is, the harder it is for the pump to generate the required pressure.

3. Feb 26, 2012

### Femme_physics

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!

4. Feb 26, 2012

### I like Serena

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.

5. Feb 26, 2012

### Femme_physics

Makes perfect sense, my sensei

6. Feb 26, 2012

### Hassan2

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.

7. Feb 26, 2012

### dushizhe

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