Hydraulics of different diameters

[Sandarsky]

I have a hydraulics question.

1” orifice valve >>>>>>>>>> 1” pipe >>>>>>>>>> 1” orifice > atmosphere

1” orifice valve >>>>>>>>>> 2” pipe >>>>>>>>>> 1” orifice > atmosphere

1” orifice valve >>>>>>>>>> 12” pipe >>>>>>>>>> 1” orifice > atmosphere

What will happen to the pressure of each? I'm assuming the larger the pipe the higher the pressure.

What will happen to the flow of each? I'm assuming the larger the pipe the higher the flow.

Thanks

 

[jblizzle]

I am not sure I understand what you are asking.
As the pipe gets larger, there is less resistance to the flow so the pressure in the pipe would be lower and the flow rate would go up (assuming fixed RPM pump).

 

[Sandarsky]

The key point I'm interesting in is what will the 1" orifices do to the system.

Will larger pipe be useless because of the smaller orifices?

 

[jblizzle]

Well the 1" orifices are certainly going to cause restriction and head loss. But the system as a whole would have lower head loss with the larger pipes.

A more realistic example would be using 2" pipe and fittings on the equipment pad will lower head loss and increase flow rate even if the suction and return lines to the pool are 1.5"

 

[mas985]

The head loss of a circular orifice is dependent on flow rate and size of the orifice. Not what is connected on the each end. However, the flow rate of the entire system is dependent on the total head loss of the plumbing and the pump connected to it.

So with the larger pipe, total head loss would go down, flow rate would go up so the head loss (pressure drop) in each orifice would go up. But absolute pressure in the pipe and orifices goes down because total head loss is lower even though the head loss in each orifice is now higher.

If you want to get into the weeds, you can read this: http://www.engineeringtoolbox.com/orifice-nozzle-venturi-d_590.html

But one thing to keep in mind is that when higher flow rates go through small orifices, it makes more noise. So while the smaller pipe might be very quiet because head loss is high and flow rates are low, the opposite is true for the larger pipe.