Hydraulics - System curve VS pump curve

In summary: I don't understand how come in the pump the more pressure there is, flow drops! 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
  • #1
Femme_physics
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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!
 
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  • #2
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
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
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
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:
 
  • #6
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

1. What is the difference between the system curve and pump curve in hydraulics?

The system curve in hydraulics represents the relationship between the total head and flow rate of a hydraulic system. It is calculated based on the characteristics of the system components, such as pipes, fittings, and valves. On the other hand, the pump curve shows the relationship between the pump's head and its flow rate at different operating points. It is a graphical representation of the pump's performance.

2. How do you plot a system curve and pump curve?

To plot a system curve, you need to calculate the total head for different flow rates and then plot these points on a graph. The resulting curve will show the head vs flow rate relationship for the hydraulic system. For the pump curve, you can obtain the data from the pump manufacturer or conduct experiments to determine the head and flow rate at different operating points. These points are then plotted on a graph to create the pump curve.

3. Why is it important to compare the system curve and pump curve in hydraulics?

Comparing the system curve and pump curve is essential in determining the operating point of a hydraulic system. The point where the system curve and pump curve intersect is the operating point of the system. This helps in selecting the right pump for the system and ensuring that the pump operates at its optimal efficiency.

4. What factors can cause a difference between the system curve and pump curve?

Several factors can cause a difference between the system curve and pump curve, such as changes in the system's components, changes in the fluid properties, and changes in the operating conditions. These factors can affect the head and flow rate of the system, leading to a shift in the curves.

5. How can you use the system curve and pump curve to troubleshoot hydraulic system issues?

The system curve and pump curve can be used in troubleshooting hydraulic system issues by comparing the actual operating point to the expected operating point. If there is a significant difference, it can indicate a problem with the system, such as a blockage or a malfunctioning pump. This helps in identifying the cause of the issue and taking corrective measures.

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