Qod 12-2-08

[Brian E. Kelly]

Originally Posted by mlarson

I'm not buying it Jae. That's like saying I need 150 VAC on the incoming line to supply all the houses in my neigborhood with 120 VAC.

Ahh the old plumbing, electrical analogy. So far the QOD has provided for an interesting discussion.

[Michael Larson]

I used to live in a River town that had it's primary water storage built into a large bluff that overlooked the city.

Water pressure was over 100 P.S.I. due to the high head of the bluff tanks.

My Dad was a plumber and type L copper was what he used as PRVs where not commonly in use.

[Jae Williams]

Originally Posted by mlarson

I'm not buying it Jae. That's like saying I need 150 VAC on the incoming line to supply all the houses in my neigborhood with 120 VAC.

Michael, the water-electric analogy is not exact science and only applies in a limited respect.

And you'll notice I said "at least" 100PSI--that's because the highest pressure given for the poll was 100PSI...most lines around here are about 120PSI.

[Jae Williams]

Actually, from the "inside the house" standpoint, both 40PSI low and 80PSI high would be the more acceptable--either is more correct thatn any other of the given possibilities.

[Michael Larson]

Jae, the analogy is quite valid.

If the city maintains 120 P.S.I in the line then that is what will appear at the residence.

[Jae Williams]

Originally Posted by mlarson

Jae, the analogy is quite valid.

If the city maintains 120 P.S.I in the line then that is what will appear at the residence.

Which is why regulators are required inside. However, quite frequently
water pressure will drop dramatically as a result of mass usage. Especially in cold weather when water mains break.

The water pressure in my house is about 60PSI and when I use a "sprinkler hose" the water pressure is equal all along the line. Then the end of the hose comes off and the pressure within the hose drops at the "sprinklers" but not at the end where it shoots out.

This is not the case with electricity. Wires connected to a main feed produce a certain amount of current (through amperage) to each terminal. If the end of the wire is cut, the current maintains its "pressure", or amperage, to each terminal--the electricity does not flow aimlessly out of the end of the wire as it does with a hose.

[Jae Williams]

The water-electrical analogy is high-school physics used to visually demonstrate the concept of amperage as a "pressure", so to speak. It really doesn't go much further than that. It does make it easier to understand that which can't be seen.

[Michael Larson]

Originally Posted by jwilliams4

The water-electrical analogy is high-school physics used to visually demonstrate the concept of amperage as a "pressure", so to speak. It really doesn't go much further than that. It does make it easier to understand that which can't be seen.

And that is the whole point of any analogy.

Most break down at some level.

[Michael Larson]

amperage is analogous to flow rate.

[Jae Williams]

Originally Posted by mlarson

amperage is analogous to flow rate.

But only as a very basic generalization.

[Michael Larson]

Originally Posted by jwilliams4

But only as a very basic generalization.

Agreed but enough for our purposes here.

[Brian E. Kelly]

Originally Posted by jwilliams4

Actually, from the "inside the house" standpoint, both 40PSI low and 80PSI high would be the more acceptable--either is more correct thatn any other of the given possibilities.

Yes Jae, but one is more correct than the other.

[Christopher Currins]

Originally Posted by bkelly2

Yes Jae, but one is more correct than the other.

I'm voting for no. 2.

[Brian E. Kelly]

At least 40 psi

[James F. McKee]

Originally Posted by bkelly2

At least 40 psi

You mean i actually got one right....yahoo...