Effect of pressure due to change in diameter of pipe

[Nitheeswar]

The pump has an outlet size of 4 inch
1) In case 1, 4 inch pipe is connected at length of 20 m
2) In case 2, 2 inch pipe is connected using reducer
In both cases the pump outlet conditions are same( having same flow rate at a given pressure)
What happens to pressure at the end of the pipe in case 2?

 

[Nitheeswar]

The pump has an outlet size of 4 inch
1) In case 1, 4 inch pipe is connected at length of 20 m
2) In case 2, 2 inch pipe is connected using reducer
In both cases the pump outlet conditions are same( having same flow rate at a given pressure)
What happens to pressure at the end of the pipe in case 2?

 

[Chestermiller]

At which end of the pipe?

 

[erobz]

In both cases the pump outlet conditions are same( having same flow rate at a given pressure)

False.

All other things the same between the two systems:

If system2 is 20 ft. of 2 inch pipe (horizontal) and you want flow $Q$ out of it, it requires a certain pressure at the pump discharge $P_2$.

If system1 is 20 ft. of 4 inch pipe (horizontal) and you want flow $Q$ out of it, it requires a certain pressure at the pump discharge $P_1$, where $P_1< P_2$.

In other words you need an effectively different pumps to achieve the flow rate in each system. Meaning impeller changes, speed changes, etc...

If you are running a positive displacement pump( aka constant volume pump) the flow rate will be equal, but not at the same pressure. The pressure adjust to whatever the systems demands at a flow with those pumps. Their pump curve is a vertical line at a fixed speed.

 

[BvU]

The pump has an outlet size of 4 inch
1) In case 1, 4 inch pipe is connected at length of 20 m
2) In case 2, 2 inch pipe is connected using reducer
In both cases the pump outlet conditions are same( having same flow rate at a given pressure)
What happens to pressure at the end of the pipe in case 2?

Isn't it one out of two: either the flow rate is the same OR the pressure is the same ?

And: doesn't it matter what's at the end of the pipe ? Atmospheric pressure, something else ?

$\$

 

[Nitheeswar]

Is this pressure difference only due to contraction and head loss in 2 inch (compared to 3 inch)?

 

[erobz]

This is a duplicated thread.

 

[Nitheeswar]

By mistake, it is uploaded 2 times.please delete it

 

[Nitheeswar]

Is this pressure difference only due to contraction and head loss in 2 inch (compared to 4 inch)?

 

[erobz]

Is this pressure difference only due to contraction and head loss in 2 inch (compared to 4 inch)?

Each piping system has its own pressure vs discharge relationship. They are not independently adjustable. It would also have to do with kinetic head consideration, not just head loss.