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Psi difference when water under same pressure exits an outlet of different diameter?
1000 gallon tank 25 feet up. The line coming down to the valve is 4 inch. One outlet is 4 inch as well, the other is only 2 inches. Will there be a difference in Psi at the outlet? If so, will the psi at the 2 inch outlet be twice as much as at the 4 inch outlet?
Don't even know why I wondered this today. Thank you for the thoughtful/informed replies.
2 Answers
- Peter HLv 79 years agoFavorite Answer
The pressures at the outlets will be the same (assuming they both open to the atmosphere). The flows will be different, because of the different sizes of tube. As the cross-sectional area of the 2 inch tube is 1/4 of the area of the 4 inch tube, as a first approximation the flow will also be 1/4 of the flow in the bigger tube (assuming both tubes are of the same length.
- JamesLv 79 years ago
It depends.
With very low flow rate, no, there will be no difference. The pressure depends only on the height of the fluid column.
However, when the flow reaches a significant volume, friction starts eating up some of the available energy in the fluid. The effort of squeezing the water through the pipe takes away some of the pressure.
The same is true when pumping water uphill, where the resulting energy loss is called "head loss" and refers to the difference between the pressure at the pump and the actual height that it can be pumped.
