Effect of changing the size of a pipe




Last Updated March 05, 2016 01:09 AM

I've had a couple questions above the sizing of a pipe, but I'm still a little confused and can't find an easy answer.

I'll use this image to get a representation of what I'm looking to have answered.

Sizes shouldn't matter, but if they were; we'll assume the small pipes are both 1/2" and the big pipe is just 3/4". What effect does it have on the water flow to increase the pipe size (into the center larger pipe)? And then what effect does it have on the flow to decrease the size?

The shape doesn't have to be a U like this; I just figured it'd knock out two birds with one stone. It simply represents an increase and then a decrease. You can treat them separately in the answers or as a whole if it does matter.

My general thoughts, from what I have been able to read through online, is that the pressure might slightly increase when going into the larger pipe or decrease when going down....

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A larger pipe, and lower velocity, has less pressure loss. The fittings in a larger pipe also have less pressure loss. So, all things considered, if you want to lose less pressure through a series of pipes and fittings, you increase the size. The trade-off is that bigger pipes and fittings cost more, and, as noted in a comment here, bigger pipes would take longer to deliver hot water.

In the example you drew, the larger pipe, and the elbows on that larger pipe would mean that you would get more of the original pressure to the fitting, rather than losing it to friction in the pipe, compared to if you went with small pipe the whole way. The difference would depend on the flow rate, which is why many different sizes of pipe exist.

There is actually an additional pressure loss introduced just by changing the pipe size (and will depend on what kind of fitting you use to do that), because the water has to change directions (flowing out or in rather than straight down the...

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Matt - Thanks for coming up with the idea and posting! Love the concept.

I followed Matt's design and read the user input and made a couple adjustments of my own.

Sorry I don’t have picture of each step, yet I wasn’t
planning on making an instructables of my own since Matt did a great job.

Blue glowing tubes - I purchased some old vacuum tubes;
then drilled holes through the box lid and placed blue LEDs under them, which
are controlled via the switch on the far right.
The LEDs are powered using a DC power supply (12v 3A output), which
provides power to all of the LEDs.

The bubbler (air pump) - I decided to purchase my own pump, which was
much smaller and could fit into the base (box) and be powered via an AC to DC adapter
and buck converter (to step 12v DC down to 3.1v DC) vs. placing the pump in the
tube on top of the lamp and using batteries.

The bubbler, which is controlled by a potentiometer

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