PDA

View Full Version : GPM Question


grassassassin
03-21-2006, 06:33 PM
I went to a house today to take in all info. Pressure is 54. Gpm is 4.28. Am I doing something wrong? Surely it has more than 4 gpm. Method to determine gpm was a 5 gallon bucket. It took 70 seconds to fill up from the outside spicket. 300/70 = 4.28. Any help would be appreciated. Thanks in advance. By the way, if this is correct how do I go about designing a system that is on over 1.5 acres?

BSME
03-21-2006, 06:42 PM
I went to a house today to take in all info. Pressure is 54. Gpm is 4.28. Am I doing something wrong? Surely it has more than 4 gpm. Method to determine gpm was a 5 gallon bucket. It took 70 seconds to fill up from the outside spicket. 300/70 = 4.28. Any help would be appreciated. Thanks in advance. By the way, if this is correct how do I go about designing a system that is on over 1.5 acres?


was that the pressure while you were filling up the bucket or was it static?

since the spigot is probably a 1/2'' line you would get more gpm out of a 1'' line when you actually made the plumbing tap

grassassassin
03-21-2006, 06:56 PM
the 54 psi was static psi. So a dumb question, how do I get a accurate gpm? I know that a 1 inch line will supply more gpm with less psi loss. So yes it is a great idea to come out with a 1 inch pipe, but how do I know what my gpm will be and my psi so that I can design the system? Remind me why I am getting this info from the spigot? Thanks for your replies.

SprinklerGuy
03-21-2006, 07:00 PM
I usually check it at the spigot like you did...if it is between 4-6 gpm....and the pressure is decent while doing so....operating pressure is different than static....then you can pretty much figure that you will get what you should with a larger sized pipe.

However......check the meter to see what size it is....you will be limited by the meter.

grassassassin
03-21-2006, 07:05 PM
That's the other problem. I checked the meter and it says 5/8 and 3/4. Don't really understand that one.

Flow Control
03-21-2006, 07:06 PM
also check for a regulator, almost standard anymore.

Ground Master
03-21-2006, 07:28 PM
what size is the service line to the meter?
are you measuring the pressure after the pressure regulator?

Critical Care
03-21-2006, 08:30 PM
Heh heh, you may also want to double check (no pun intended) to see if you have a double check valve assembly in line, or a PVB with a valve not fully open. Never know…

bicmudpuppy
03-21-2006, 08:55 PM
Is there more than one hose bib? Attach your pressure gauge and then open the other bib and check your pressure. If your getting 4+gpm from a 1/2" hose bib and maintaining a decent operating pressure, then I would say you have the ability to put in a system. Your not going to be real productive watering 1.5A w/ a 5/8" meter, but you could design a system that would provide enough water to keep things "alive" during droughts and supplement normal rain in the spring and fall for a nice turf.

Dirty Water
03-21-2006, 09:38 PM
We've done a handfull of systems that only had 4-5 gpm to play with. Most were on real low output wells.

The trick is small nozzles, lots of zones, and long watering times.

We have one system that is rather large and runs from midnight to 8 am.

grassassassin
03-21-2006, 11:14 PM
I wanted to thank all of you for your time and input to my questions. I'll post again as soon as I have some more info from the house and the meter at the house.

Currier
03-21-2006, 11:43 PM
MP rotator time.

Dirt Boy
03-21-2006, 11:58 PM
I can't say I'm an expert, but, you may wish to click over to: http://www.irrigationtutorials.com and read Jeff's tutorial.
#1 You shouldn't use the "faucet & bucket" method to determine flow.
#2 Watering that much area with that small of supply, is not going to work very well.
But, like I said, I'm not an expert, and what I said is just what I read.

Regards

Wet_Boots
03-22-2006, 09:26 AM
If you have over an acre-and-a-half to water from a 5/8 meter set on a 3/4 supply line, with 54 psi static pressure, there probably will not be enough hours in a day to properly water the entire property. Explore upgrades or alternatives to the existing water supply.

PurpHaze
03-22-2006, 09:27 AM
Personally, I also feel it's going to be a little dicey watering 1.5 acres with what you're telling us you have. Not that it can't be done but your choice of sprinklers/nozzles will need to be watched very carefully.

RE: the meter... if it says 5/8 x 3/4 then it means the meter size is 5/8" and the inlet/outlet sides are 3/4". You'd use the specs on both to determine if your meter is adequate.

Flow Control
03-22-2006, 09:48 AM
never got the whole 5/8 meter thing until it was explained to me on this board or through the water department.

Critical Care
03-22-2006, 02:04 PM
If the minimum static water pressure of the supply going to the meter is 120 psi, then a system based upon the 5/8” meter could be designed at 15 gpm. It would be 18 gpm except that you’re limited to 75% of the meters safe flow. But because of the service line size, you would have to limit the design to probably no more than 10 gpm max. You just have to go with the weakest link type of thing. Umm, and of course, you probably won’t have 54 psi pressure once you figure in the losses through all the devices and pipe. If that service line is 200’ of ¾” schedule 40, then you’ve probably already lost more than 10 psi.

If for some reason 5 gpm is all that is available, then anyone taking a shower in the house would more than likely notice a problem whenever a toilet was flushed. With 1.5 acres needing to be irrigated you tend to get the idea that at 5 gpm you’d be stuck watering a lot of zones at long hours. This would surely be a problem during the hours whenever people are up and about taking showers, washing clothes, or whatever.

Mdirrigation
03-22-2006, 05:34 PM
Since this is city waterand you took the readings in March they are probably on the high side . When summer hits and more people are using water the presure and the flow will probably drop .

Check 2 neighbors houses , I have found that on occasion the customers house may have a blockage in the house supply (stones usually ) or the supply line is kinked . If the neighbors have more flow and pressure than your customer has a problem .

Flow Control
03-22-2006, 06:06 PM
never got the whole 5/8 meter thing until it was explained to me on this board or through the water department.
Back in the day all homes were plumbed in 5/8 pipe. That is why the meters are still 5/8. Around here you either have a choice of 5/8 or 1" for homes.

tomcl
03-22-2006, 06:59 PM
Are you sure that your bucket is exactly 5 gallons--Alot of buckets that look like 5 gallons are really bigger than that--Pour in 5 gallon jugs of water-mark the line and then remeasure--Or you could buy a flow meter, psi setup--Looks way more professional

hope I could help--

AssuredServicesCo
03-23-2006, 01:25 AM
To determine the water supply you can use for irrigation at a specific site consider the following 3 rules:

1. Pressure loss through the water meter should not exceed 10% of the minimum static water pressure available.

2. The maximim water flow through the meter should not exceed 75% of the safe flow of the meter.

3. The velocity of the water flow should not exceed 9 feet per second (copper) or 5 feet per second (pvc).

Each of these three rules give you a gallons per minute answer. Then choose the average or the low end if you want to be conservative.

If a pump is being utilized , be sure to note the model, orsepower and any other visible charachteristics that may aid in getting accurate pump statistics from the manufacturer in order to design properly.

Clear as mud?

bicmudpuppy
03-23-2006, 01:48 AM
I will admit that I rarely do an accurate flow test. Unless I am in serious doubt, I just don't put that much work into it. Pressure guage on hose bib y and open hose bib x. If Y pressure doesn't drop significantly and I have an adequate static pressure, then I design a 5/8 meter system to stay under 15gpm and I don't have problems. If I cannot maintain a decent pressure at y with free flow at x, then I either use a handy dandy flow meter or I clock the meter running for 30 seconds and find flow that way. Usually, I will first close hose bib x to a point that the pressure at y is acceptable. Target of 40 psi. The flow I have at a sustained 40psi is my max design flow. These are the situations that make guys love the MP rotators or a head like the CR500 that will operate reliably at 30psi.

Critical Care
03-23-2006, 02:07 PM
Mike, those were the rules that I used in my last post to surmise what his situation might be. And in this case he’ll probably be limited by rule #3 if that’s only a ¾” service line, copper or pvc.

Say what Bryan? Well yeah, I’d be interested in knowing what happens to the pressure at point X when someone flushes toilet Y.

jerryrwm
03-23-2006, 04:45 PM
...Say what Bryan? Well yeah, I’d be interested in knowing what happens to the pressure at point X when someone flushes toilet Y.

If I had to guess, I'd say it went right down the crapper.

bicmudpuppy
03-27-2006, 04:41 PM
If I had to guess, I'd say it went right down the crapper.
ROFLMAO, I sure hope that is where anything that got "flushed" went or somebody had a mess to clean up.

PurpHaze
03-27-2006, 10:38 PM
Anything like, "Hey! What's that floating in my main line?" :laugh: