How do I calculate my garden hose PSI?

Question

I want to purchase a pond vacuum which requires about 40 PSI. I don't need an EXACT measurement, just something to go by. The garden hose is a standard type, half an inch diameter, about 50 feet long on a slight incline and I've measured the water flow to be about 10 to 12 gallons per minute.

Answer 1

Save yourself the trouble of guessing. There are too many variables involved, including the limiter that may exist at your meter. You can get a gauge to measure the PSI directly at a hardware store like Lowes (link below) for about $6.00. It'll screw right onto your outside tap or your hose.

http://www.lowes.com/lowes/lkn?action=productDetail&productId=73222-18701-0069770&lpage=none

If they're not giving you 40lbs, that'd be pretty lame, though.

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Answer 2

For a start contact your water utility and ask what pressure is in the main under the street at your house. You will get an answer of about 50 psi usually. That pressure comes from the elevation of the local water tanks and maybe from booster pimps installed if the utility finds you local pressure is too low for users and for firefighters. Now all of the restrictions in the supply plumbing and in the hose as well as that slight incline are acting to reduce that but probably not down below 40. One way to get more exact is to purchase a pressure gage that is attached to a garden hose fitting.

Answer 3

If you are really looking a 40 psig of positive pressure in a 1/2" -3/4" garden hose, I believe you will be well within the design working range. There is no way to calculate such a working pressure from the information at hand. In general smaller diameter pipe and tubing ace will handle much higher pressures than larger tubing of the same construction.

About the vacuum, you can only achieve about 15 psig of vacuum with any system (on Earth). Just as with positive pressure, small diameters are less likely to collapse under vacuum than larger. Even a 5/8 -3/4" hose would probably be fine for the maximum attainable vacuum of ( -) 15 psig.