How to increase psi in my gravity irrigation system?

[pmsmechanic]

Sounds like an interesting project.

 

[plowhog]

Can you either provide a fairly detailed sketch of your system, or at least whether the water box is SEALED or OPEN? Thanks... Steve

It is sealed only from the intrusion of debris. The water box is not under pressure, so you are correct that the "head" starts at this water box. Downstream (downpipe) from this box, the piping to the irrigation is a sealed system.

I was wondering if I connect the incoming 6" line to the 2 1/2" irrigation line if it would increase the PSI for my irrigation sprinklers. I think it will as the "head" would be up higher at the elevation of the 6" pipe.

But if I do that, I don't know how much psi gain I would get, as I don't know the amount of fall on the 6" line. It is very long, through a heavy forest of rolling terrain, and difficult to measure.

If I connect the 6" and 2 1/2" pipes I would have to somehow deal with a new overflow. There is no overflow at the initial source of the 45gpm going into the 6" pipe. Connecting those two pipes would cause me to "lose" the 3" overflow down to the pond.

Here is a diagram.

 

[BukitCase]

Weren't you gonna test your 6" line's pressure by a temporary cap and pressure gauge? That would tell you what that 6" line's static head is. If it's more than the 10 pounds you wanna gain, AND you have a way to support 24' of vertical 3" pipe, you could tee off the 6" line into a 3" VERTICAL stand pipe, then let the TOP of THAT drain back into the water box for overflow to pond - this would keep your sprinkler pressure constant (assuming you don't run out of water, or add more sprinkler heads)

Then, if you can find the parts, tie the 6" to the 2-1/2" in as STRAIGHT a line as possible, preferably thru a series of bell reducers for a more gradual transition. The "tall overflow" at 24' vertical will give you about 10-1/2 # more head than you have right now (actual head of water at sea level is 27.65" = 1 psi)

Kinda hokey, but physics-wise, it'd work... Steve

 

[plowhog]

you could tee off the 6" line into a 3" VERTICAL stand pipe, then let the TOP of THAT drain back into the water box for overflow to pond - this would keep your sprinkler pressure constant (assuming you don't run out of water, or add more sprinkler heads)

That is an interesting mostly fault-free pressure regulator (unless the pipe were to get plugged somehow.) Very interesting.

I am going to add a threaded 6" coupling on the end of the 6" pipe. Then I can work from that to test pressure then do further plumbing as needed. The threaded fitting (and a reducing bushing) were not in stock so I had to order those. When I get them I will test the pressure.

 

[BukitCase]

If you find you have enough head from the pressure test and decide to go ahead with the plan, I would NOT use bushings for the reduction - the bell reducers

429-532 - Spears 429-532 - 6" x 4" PVC Schedule 4 Reducer Coupling

429-421 - Spears 429-421 - 4" x 2-1/2" PVC Schedule 4 Reducer Coupling

have noticeably LESS ABRUPT changes, which will cause less turbulence - and turbulence increases flow resistance. Ideally, such a reduction would be done with a custom piece of pipe that TAPERS from 6" ID down to 2-1/2" ID over several FEET - it's been a long time since I studied this, but you might actually be able to FIND such a beast where alternate energy stuff is sold. If you're interested, try googling "pelton wheels and supplies", it may lead you to something... Steve

Oops, never mind - musta been thinking of something else; 45 years of dust on brain cells can do that I guess
Pelton wheel - Wikipedia

You'd still be better off NOT using bushings tho... Steve

 

[dnw64]

Weren't you gonna test your 6" line's pressure by a temporary cap and pressure gauge? That would tell you what that 6" line's static head is. If it's more than the 10 pounds you wanna gain, AND you have a way to support 24' of vertical 3" pipe, you could tee off the 6" line into a 3" VERTICAL stand pipe, then let the TOP of THAT drain back into the water box for overflow to pond - this would keep your sprinkler pressure constant (assuming you don't run out of water, or add more sprinkler heads)

Then, if you can find the parts, tie the 6" to the 2-1/2" in as STRAIGHT a line as possible, preferably thru a series of bell reducers for a more gradual transition. The "tall overflow" at 24' vertical will give you about 10-1/2 # more head than you have right now (actual head of water at sea level is 27.65" = 1 psi)

Kinda hokey, but physics-wise, it'd work... Steve

That is an interesting mostly fault-free pressure regulator (unless the pipe were to get plugged somehow.) Very interesting.

Yeah.

Agreed that finding the potential additional head is a first step. If there is, and since apparently there is a concern with extra flow spilling at the source(?). So I would consider this:

Connect the 6" to the 2.5". Rather than using a pressure regulator, add a T at that joint, pointing up, and add pipe vertically as needed to control the pressure. Excess can fall into the current water box. According to previous posts (I didn't figure it myself) 20' will give you the extra 10 PSI. This will only work if the source is more than 20' higher than the water box.

If you have less than the 20' of additional head, but close enough to make it worthwhile (maybe 10-15') put the T at the source, with a drain pipe (could be "firehose type", cheap plastic stuff) going to wherever it is that you can safely get rid of the extra, whether the current water box or whatever.

 

[BukitCase]

Crap, dnw64 - dunno how I missed your previous post or I would've pointed it out in mine; I don't like not being credited when I post useful stuff, and I try NEVER to do things to/for others that I wouldn't appreciate myself, so please accept my apology :ashamed:... Steve

 

[plowhog]

Crap, dnw64 - dunno how I missed your previous post ...

Same for me! I think due to the uncertainty of the psi I started thinking about that. Anyway, to both, great idea!!

 

[dnw64]

Crap, dnw64 - dunno how I missed your previous post or I would've pointed it out in mine; I don't like not being credited when I post useful stuff, and I try NEVER to do things to/for others that I wouldn't appreciate myself, so please accept my apology :ashamed:... Steve

Apology not needed, but thanks

 

[plowhog]

I used a self leveling laser and measured distance and drop.

The pipeline is 550 feet long in this section. There is 38 inches total drop from intake to exit. As I said, it is a very shallow grade.

When I was doing the survey I found two spots where tree roots, over time, lifted the pipe up. In those two spots, instead of having fall, the pipe ran uphill for a short section of about 30 feet. One section ran uphill to a point 2" higher than where it started, the other section was 2 1/2" higher. I excavated below those "high spots" and eliminated them. After I did that, flow increased to 50 gpm.

With only 38 inches of total fall it doesn't appear I have any worthwhile psi gain that is possible from gravity feed?