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Saturday, December 31st 2011, 4:42pm

Super High PSI ... moderetly low GPM?

PSI = 175
GPM = 17 (bucket test) / 18 chart
Total Grass Sq/feet = 3500

Meter is at the street and runs 1" copper to the home, comes up, then goes down to 3/4 copper after a shut off valve. Then splits off, 1 to the unregulated sprinklers/hose system; 1 to a Wilkins 600 pressure regulator to the home. Current system is all galvanized up to the valves and after is mostly schedule 40 PVC.

Since the 3/4" pipe where I would splice the sprinkler into would be less than 5 feet in length, I plan on calculating the size at 1" (correct?)

After doing some searching and reading it's apparent that 175PSI is just to high for ... we'll pretty much everything. However, what I couldn't really find information on is how reducing the PSI is going to effect the GPM. Assuming I put in another pressure regulator on, how will that effect the flow rate (GPM)? (The reading I've done so far seems to imply the PSI is totally irrelevant ... but I cannot get a definitive answer.

Can anyone suggest a good regulator for my purposes?




Posts: 2,395

Location: USA


Saturday, December 31st 2011, 8:28pm

175 sounds really high to me. Make sure there's no air in the pressure tester and test again. What I do is I don't tighten the tester all the way. Then I turn the hose bib on so the air can get out. It will be leaking water. Then I tighten while the bib is still on. You'll get a more accurate reading that way. With air in the tester you can get crazy readings like 175.

Also make sure you don't connect copper pipe directly to galvanized. Electrolisis will erode the connection.


Supreme Member

Posts: 482

Location: Houston, Texas


Sunday, January 1st 2012, 12:29am

I think I understand.

First thing, 17 G.P.M. is not low.

If you need to use more valves use more valves.

Your question is how will pressure affect G.P.M.
Can you get the regulator and let us know how it changed? I am curious because in Houston we generally have 55 to 60 PSI static pressure and water meters usually give us 10 to 12 G.P.M. on a residential 5/8 meter. With Galvenized Pipe it is like a box of chocolate's and how old it is. My humble Opinion, I would find a different material than galvenized if at all possible. I recently replace my house line from the 1940's that was galvenized and I could hardly see through my 12" piece of pipe with all the crud in the line. I replaced 140 ft and noticed a huge improvement.
I guess you can see why I cannot comment on a regulator for you as I have little experience with them.
Happy New Year :thumbsup:
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LI0006121, BPAT0011021, CI0009500


Sunday, January 1st 2012, 12:59am

I figured 17 GPM was good ... but since the PSI was so high I thought maybe it would drop with a regulator.

I should have mentioned that although the current system is primarily galvanized, I'm redoing the whole system. So it' will be copper to the house and PVC for everything else. Still working on the plan.

As far as the PSI goes, I've used 2 different gauges run on every unregulated faucet. The static PSI is 175 for sure, even when I open up another faucet all the way on the same line it only drops to 160 PSI.

In all these "planning" packages, or items I'm reading about. It never really accounts for such high pressure. I suppose I'll have to get a regulator and see ...


Supreme Member

Posts: 309

Location: Northern New Jersey


Sunday, January 1st 2012, 7:52am

Call the town's water dept and see what they say. If they say 175 is what they supply, done.

As far as pressure regulators, Febco makes popular PVBs. I would look into a Febco regulator.

As far as 17 gpm, good for you. I have half that.


Supreme Member

Posts: 5,331

Location: Metro NYC


Sunday, January 1st 2012, 11:13am

If you are in an area that has a Wilkins distributor, then stay with that brand, only look to the newer model BR4, which gives you higher pressures that sprinkler systems can require.There is a significant loss in a PRV, but starting with 175 psi gives you pressure to burn.


Supreme Member

Posts: 493

Location: Seattle


Tuesday, January 3rd 2012, 2:06am

We have a few area's with 175 psi .. It's pretty insane
From experience and if you follow a flow chart 17 GPM on a 3/4 line with 175 psi is actually pretty low gpm. If you had the 3/4 copper line cut fully it would probably be 30 gpm+. Depending on several factors

However the higher the psi the more pressure loss happens and water hammer. Ontop of the galvi corrosion /hose bib is probably how you got your gpm.

I Highly Highly Highly Highly recommend to install a a pressure reducing valve AT your water meter ( Just after) You can request your water district to install one prior- they may or may not do this though.. The reason I recommend this is because of possible future leaks in your service line leading to your house. I deal with leak detection on service lines a lot and the pressure plays a huge role in the leak. I've seen many leaks just stop with reduced pressure... This pipe is your responsibility not the cities.

To code an irrigation system is rated for 5 FPS (Feet per second)

If you follow this flow chart

This is just an example.

But lets say you want 70 PSI leading up to the irrigation system and to the PRV at the house.

To set the PRV correctly at the meter Calculate your length from the meter to your house and the elevation difference .

For example if your house is 100' from your meter with a 20' elevation gain. Pressure loss from the elevation gain is .45 ( rounded up from .433) per foot. so 20x .45 = 9PSI . Factor in to reach the goal of 12 GPM on a 1" copper line ( 5 FPS) of 100' your water pressure loss is an aditional 5 fps. Altogether rounding up to a total of 15 psi

So to reach 70 psi at your house in this situation you must set the PRV at the meter to 85 PSI. It may be confusing but I recommend to do this.


Tuesday, January 3rd 2012, 12:24pm

Thanks for everyone's responses. I'll contact the water district (Los Angeles Department of Water and Power) and see what they have to say ... hopefully I'll be able to speak to a human.

By the way, the elevation grade on my home would be something very minimal... is there an easy way to measure this or is "eye-balling" good enough?


Monday, January 9th 2012, 12:17pm


1" Meter
MAX - 189 PSI
MIN - 122 PSI

... so I guess I'm not crazy after-all... time to get a pressure reducer ...


Advanced Member

Posts: 67

Location: South Jersey


Monday, January 9th 2012, 1:23pm

That's incredible. I would have been happy with less than half that.

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