How to increase psi in my gravity irrigation system?

[jaxs]

Why do you doubt 6” pipe is flowing 45 GPM? It is capable of way more which would explain it being only 1/4 full. Even if the 6” pipe is 4” pipe it’s still easily doable. A good water hose can probably push 1/3 that much.

I don't doubt that it is flowing 45GPM,but under present conditions, I doubt it can be made to flow 45GPM at 45PSI. The 45 GPM is presently near 0 PSI. It isn't necessary for you to understand what I say,just tell the man how to accomplish what he want's and stop asking pointless questions.

 

[4570Man]

I don't doubt that it is flowing 45GPM,but under present conditions, I doubt it can be made to flow 45GPM at 45PSI. The 45 GPM is presently near 0 PSI. It isn't necessary for you to understand what I say,just tell the man how to accomplish what he want's and stop asking pointless questions.

I’ve already told him that. Raise the head height is the only way. And agree that it’s not 45 psi flowing. It’s almost certainly measured static pressure like I said in the first few post.

 

[RedNeckRacin]

If the 6" pipe has a nice smooth bore it could easily be flowing 45gpm. The inlet is in a tailwater controlled condition. It isn't really relevant unless we aren't getting 45gpm then we could look at a head wall or something to reduce the inlet flow restriction from I assume a sharp orifice opening. Thanks for posting the pressure loss stuff some other members may not have much familiarity with that.

I think we need to look at a static pressure test on this 6" pipe before we get to many wild ideas going. Also, A quick rough estimate of the elevations would be a topo map or Google Earth you can just hover over the Google Earth map and it should get you within 5 feet or so. It's not real precise but it's still better than nothing. Might rule out gravity all together or it might have plenty of fall and we would just need to figure out what to do with the excess water coming down the line.

 

[dnw64]

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.

 

[plowhog]

I think we need to look at a static pressure test on this 6" pipe before we get to many wild ideas going. Also, A quick rough estimate of the elevations would be a topo map or Google Earth you can just hover over the Google Earth map and it should get you within 5 feet or so.

The two ends of the 6" pipe are both in heavily forested areas with full canopy overhead. I have a GPS and will try for a signal, but I'm not too sure I can get reception. Google Earth only shows forest canopy-- I can't find any landmarks.

Could I approximate the elevation drop using PSI measured in the 6" pipe? I could cap the "outflow" end of the 6" pipe and put a PSI gauge on the cap. Then let the pipe fill and read PSI?

I presume if I see 20 psi at the capped off 6" pipe then I have about 46 feet of elevation drop (20 / .43)?

The wild card would be air stuck in the pipe that could not get out. Due to the very shallow gradient on the 6" pipe I presume there would be some trapped air even if the pipe was filled?

 

[jaxs]

The two ends of the 6" pipe are both in heavily forested areas with full canopy overhead. I have a GPS and will try for a signal, but I'm not too sure I can get reception. Google Earth only shows forest canopy-- I can't find any landmarks.

Could I approximate the elevation drop using PSI measured in the 6" pipe? I could cap the "outflow" end of the 6" pipe and put a PSI gauge on the cap. Then let the pipe fill and read PSI?

I presume if I see 20 psi at the capped off 6" pipe then I have about 46 feet of elevation drop (20 / .43)?

The wild card would be air stuck in the pipe that could not get out. Due to the very shallow gradient on the 6" pipe I presume there would be some trapped air even if the pipe was filled?

I believe that is an excellent idea and should yield an accurate estimate. Trapped air wouldn't alter psi reading.
Will you clearify a few things? Is the 35psi at outlet of 2.5 pipe WHILE IT IS FLOWING 45GPM or was pipe caped when pressure was being read? Pressure regulator has been mentioned more than once and you said you found them overly expensive. How might a pressure regulator help overcome the problem. I would think if you were lucky enough to boost pressure above what's required for the sprinklers,a ball valve on 2.5 pipe could regulate sprinkler pressure. What is the estimated storage capacity of water box. Stated differently,if flow from 6" suddenly stopped,how long could water box sustain 45GPM?

 

[plowhog]

Is the 35psi at outlet of 2.5 pipe WHILE IT IS FLOWING 45GPM or was pipe caped when pressure was being read?

If flow from 6" suddenly stopped,how long could water box sustain 45GPM?

35 psi with everything off, Static pressure. I maintain 35 psi, or close, while doing irrigation as long as incoming available water exceeds water demand from sprinklers. Which seems to make sense as the pipe should stay completely full as long as usage doesn't outstrip supply.

The water box is maybe 5 feet by 5 feet by 2 feet high. Just large enough for the 6 inch line to dump water in it from above, room for a few mesh screens to remove debris, and room for pipes going out.

The 2 1/2 inch line (irrigation water) penetrates into the wall of the box about 3 inches from the bottom. An additional pipe, 3 inch diameter, penetrates higher up on the wall above the level of the 2 1/2 inch line. That is an overflow, which is piped directly to my pond.

Since the 2 1/2 inch pipe is the lowest, it has priority. If I use or exceed 45 gpm, all incoming water will go out the 2 1/2 inch line and the water level will not rise up to the overflow. But if I use less water for irrigation, or turn the entire irrigation system off, the water level in the box rises and then goes out the 3 inch line which acts as an overflow.

 

[RedNeckRacin]

The two ends of the 6" pipe are both in heavily forested areas with full canopy overhead. I have a GPS and will try for a signal, but I'm not too sure I can get reception. Google Earth only shows forest canopy-- I can't find any landmarks.

Could I approximate the elevation drop using PSI measured in the 6" pipe? I could cap the "outflow" end of the 6" pipe and put a PSI gauge on the cap. Then let the pipe fill and read PSI?

I presume if I see 20 psi at the capped off 6" pipe then I have about 46 feet of elevation drop (20 / .43)?

The wild card would be air stuck in the pipe that could not get out. Due to the very shallow gradient on the 6" pipe I presume there would be some trapped air even if the pipe was filled?

You are correct. We can get a rough estimate of the elevations with a pressure check. The Google Earth idea was also a rough idea for elevations but the direct measurement would be best!

 

[BukitCase]

I just re-read the entire thread, and nowhere is it mentioned whether the "water box" is SEALED, or open to atmosphere - if the box is open to atmosphere, then the head from there DOWN is the only pressure your sprinklers will see.

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

 

[jmc]

I just re-read the entire thread, and nowhere is it mentioned whether the "water box" is SEALED, or open to atmosphere - if the box is open to atmosphere, then the head from there DOWN is the only pressure your sprinklers will see.

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 has a vent for overflow- so 'open'.