Adding pipes for compressed air delivery

[yun]

Hi all! I have a problem here, anyone here knows what will be the effect on pressure and flow rate of compressed air by adding additional pipes leading out from my compressor? For eg. if i were to increase the number of delivery pipes from 1 to 2, will the flow be slpit evenly between the two pipes? And will pressure across each pipe drop too?

WOuld really appreciate any ideas, opinions i can get!

Thank you!

 

[mfb]

It depends on the whole setup. If it is symmetric with respect to the pipes, flow will be split evenly and pressure drop in the pipes will be reduced.

 

[Travis_King]

It also depends significantly on where those pipes are going (i.e. what equipment are they feeding? Is the demand continuous?)

 

[yun]

Hi travis, the pipes lead to a diffuser about 6m deep. It is for aeration purposes. Demand wise, sometimes demand is long and continuous (4hrs or longer), at other times it is short and intermittent (10mins on, 10mins off etc.).

 

[Travis_King]

There aren't really rules of thumb for how additional lines will affect your system beyond what's been said. If you want to understand how the system will be affected, you'll need to complete an analysis of the flows and pressures based on various operating conditions. (max, nominal, and min loads, different set points, whatever you want to see).

Air is like any other liquid. It flows from high pressure to low pressure and will take the the path of least resistance.

 

[yun]

Hi mfb, apologies, i didnt post my reply to you. Thanks for your reply anyway! Can i clarify please, am i right to say that from what you stated, assuming that the system is symmetrical, flow will be halved such that each pipe will have equal flow and pressure in each pipe will be higher than when there was only one pipe?

Thank you!

 

[mfb]

am i right to say that from what you stated, assuming that the system is symmetrical, flow will be halved such that each pipe will have equal flow

If the system is symmetric, flow cannot be asymmetric (unless the symmetry is an unstable state, but I would not expect this), right.

and pressure in each pipe will be higher than when there was only one pipe?

The pressure difference will be smaller.

 

[Travis_King]

To add to what mfb is saying:

If the piping characteristics, fittings, valves, and end loads of the system are the same, then a symmetrically designed piping system will see symmetric flow.

As mfb said, the pressure difference will be smaller. That is, if you keep the same flow into the entire system such that pipe 1's flow is halved and pipe 2's flow equals that of pipe 1, the air will experience less pressure losses due to the flow velocity (friction).

As I noted, though, if the system is otherwise asymmetric, then how the flow will divide will depend on the specific conditions of each leg of the system.

 

[yun]

mfb and travis, thanks for the clarification. indeed, it is not quite possible to make the system symmetric. However, assuming that it is, say that i have pipe a compressor initially delivering compressed air at 6 bar, with only one pipe, the pressure in the pipe may only be 5 bar due to pressure losses. However, if i add an additional pipe, each pipe may have 5.5 bar due to less flow velocity?

 

[mfb]

The pressure at the end will increase, if the pressure at the source (and the total flow) stays the same. It might be 5.5 bar, but it could be something else, too.

 

[yun]

dear mfb and travis, thanks for your replies! If possible, do yall mind elaborating more on why the above is so? Otherwise, you have already been very helpful :)

 

[mfb]

A higher velocity of the air leads to more friction, which requires a higher pressure drop per length.