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Poly Pipe Mainline question

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jermeyg2gmail.com

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Wednesday, October 17th 2012, 4:45pm

Poly Pipe Mainline question

Hello, I got myself a well installed recently and it tested to have a 60psi at 16gpm or 50psi at 20GPM. I followed the irrigation tutorial and design for 16gpm. I followed the irrigiation tutorial pretty much to a tee walking through the design process from start to finish however I am digressing from the mainline suggestion of using PEX. The area of the install is KS and the frostline is 18inches. From what I understand most installlers here use 1"poly for everything however, I would like to size my mainline to 1 1/4 and 1" laterals. When ordering the mainline I assumed that 100psi would be fine seeing that my design pressure is 60psi. However during some research I read on here and the lawnsite I am wondering if this is a bad idea. The 1 1/4" poly is made by SilverLine Plastics and its the Max-Flo utility grade poly. I believe it is not NSF rated as well. I understand that the mainline is not under constant pressure as it would be with a city hook up but I am thinking I should also design my system such that if my well drys up I could switch to city in the future.



So, would 1 1/4" 100PSI Poly mainline be acceptable? I noticed the difference in wall thickness to 125PSI is 0.60" increase.

Also, for my lateral lines I am using 80psi NSF rated lines which seems to be the common standard around here. Is that acceptable?



For what its worth I am going to attach my design incase someone sees anything that might jump out at you. Thank you for any advice or corrections!

Rotors I20

Sprayer PROS-04-CV

PGV101G

Wet_Boots

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Posts: 4,102

Location: Metro NYC

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Wednesday, October 17th 2012, 5:39pm

Unless you know your city water supply can match the well, with pressure to spare, don't worry about switching supplies.

You don't have utility-grade poly under 24/7 water pressure, so your system must be designed accordingly. I don't know from Silverline poly pipe, so no first-hand opinions from me.

jermeyg

New Member

Posts: 3

3

Wednesday, October 17th 2012, 8:13pm

Quoted from "Wet_Boots"

Unless you know your city water supply can match the well, with pressure to spare, don't worry about switching supplies.

You don't have utility-grade poly under 24/7 water pressure, so your system must be designed accordingly. I don't know from Silverline poly pipe, so no first-hand opinions from me.
Okay, I found out that the city water supply is roughly 50 psi at 15gpm although I know that it would be user specific so I won't worry too much about that as you suggested.

Concerning the mainline poly, are you suggesting that I switch to a NSF rated polyline? Do you have a suggestion on psi rating? Thank you for your help so far. I appreciate it!

Wet_Boots

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Location: Metro NYC

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Thursday, October 18th 2012, 9:31am

If the well install has a pressure tank and a pressure switch controlling pump operation, you are probably fine. If pump operation will be controlled by a relay, then it's a different story, since the pump can probably generate higher pressure than the pipe can withstand. You will then have an absolute need for a pressure relief valve at the wellhead. For relay control, you definitely upgrade the mainline pipe, since there is no protection afforded by a pressure switch and pressure tank, and you must always allow for a zone valve not opening when energized.

You aren't restricted to just poly and PEX tubing. There is also sch 40 PVC, which will have a much higher pressure rating, at a competitive price. (I'm assuming pipe will be laid in open trenches)

jermeyg

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Posts: 3

5

Thursday, October 18th 2012, 11:42am

Quoted from "Wet_Boots"

If the well install has a pressure tank and a pressure switch controlling pump operation, you are probably fine. If pump operation will be controlled by a relay, then it's a different story, since the pump can probably generate higher pressure than the pipe can withstand. You will then have an absolute need for a pressure relief valve at the wellhead. For relay control, you definitely upgrade the mainline pipe, since there is no protection afforded by a pressure switch and pressure tank, and you must always allow for a zone valve not opening when energized.

You aren't restricted to just poly and PEX tubing. There is also sch 40 PVC, which will have a much higher pressure rating, at a competitive price. (I'm assuming pipe will be laid in open trenches)

Wet, thank you for the response I really do appreciate the help. The well is for irrigation only and from what I understand has only a submersible pump in the casing. It will be operated by a relay and from talking to the well/pump installer the pump will pressurized against a closed valve until failure or the timer had changed valves. There is absolutely no smarts in the pump to relieve the pressure. This was not something I even considered so thank you for bringing this up.



Okay now I need to research relief valves. When I spoke to the well installer about this they said you can do this but typically you end up with a mess on your hands when the valve doesn't open, however I am thinking that a mess is cheaper than a overheated pump. Do you have any advice on relief valves?



You are correct that all pipe will be laid in trenches. Stupidly I already built my manifolds with 1 1/4 barb fittings/slip fitting since at the wellhead and each manifold I am using PVC. So I would need to return all fittings and rebuild for PVC. I can understand your suggestion for SCH40 as the trenches are open and the fittings would be pretty easy to work with.



My trenches are 18" deep (frostline) and there are minor curves so SCH40 isn't out of the picture. However, if I were to stick with Poly what PSI rating would you recommend given all the complications?



Thank you for your help.

Wet_Boots

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Location: Metro NYC

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Thursday, October 18th 2012, 3:36pm

You might consider skipping the relay in favor of a pressure switch and a small pressure tank, and to use a master valve to feed the system, so that the mainline is not under pressure 24/7 ~ the advantage of such an approach is that you aren't subjecting the mainline to excessive pressure

I looked at the design, and I don't see that you are matching zone flows to the pump performance. The pump doesn't just set a ceiling for zone flows. It also sets a floor. You need a certain minimum flow in order for the pump to not be short-cycling. I know this is where people think that relay control is better than pressure switch control, as it forces continuous operation, but what will be the mainline pressure if a zone is only using a fraction of the pump output? The answer to that question is that the pressure will be higher than you'd like. How much higher is an answer that will tell you what pipe your mainline must be.

By the way, your zone valves need to have flow controls if the supply pressure may be excessive.

One means to get a handle on pump operation and system pressures is to employ something like a Cycle Stop Valve upstream of a tank and pressure switch. That would let you employ a master valve and a mainline of the ordinary 100 psi poly.

jermeyg

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Posts: 3

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Friday, October 19th 2012, 11:21am

Quoted from "Wet_Boots"

You might consider skipping the relay in favor of a pressure switch and a small pressure tank, and to use a master valve to feed the system, so that the mainline is not under pressure 24/7 ~ the advantage of such an approach is that you aren't subjecting the mainline to excessive pressure

I looked at the design, and I don't see that you are matching zone flows to the pump performance. The pump doesn't just set a ceiling for zone flows. It also sets a floor. You need a certain minimum flow in order for the pump to not be short-cycling. I know this is where people think that relay control is better than pressure switch control, as it forces continuous operation, but what will be the mainline pressure if a zone is only using a fraction of the pump output? The answer to that question is that the pressure will be higher than you'd like. How much higher is an answer that will tell you what pipe your mainline must be.

By the way, your zone valves need to have flow controls if the supply pressure may be excessive.

One means to get a handle on pump operation and system pressures is to employ something like a Cycle Stop Valve upstream of a tank and pressure switch. That would let you employ a master valve and a mainline of the ordinary 100 psi poly.
Wet_Boots, you gave me lots of good information to consider and what you are talking about makes perfect sense in my mind and operation. I check out the website and understand what is going on. From what I gather the cycle stop valve does keep the mainline under a pressure however you get to set that pressure which makes sense. Instead of the pump pushing against a deadhead or close valve it pressurizes a tank till it reaches the cutoff value of the pressure switch. A pressure tank out in the yard would be an eye sore but certainly seems like the right way to irrigate from a well.

I had not thought about the fact that my flow would be variable depending on the zone running and yes you are correct that I only set my zones to be less than the ceiling and not understanding the pressure differential for a zone utilizing less GPM.

I think a pressure relief would be a good idea so that if a valve is stuck I am not overpressuring the lines. Also I think upgrade my polyline to 125psi which is what is in the well might be a good idea. Perhaps a pressure reducing valve would be a good option to use since the cycle stop valve without a tank or pressure switch is essentially the same system?

Wet_Boots

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Location: Metro NYC

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Friday, October 19th 2012, 9:02pm

Just to be clear, a device like a Cycle Stop Valve, actually is a pressure regulator, with a tiny bypass in it to allow the pressure switch to operate. The pressure tank can be a very small one. Also, the plastic CSVs have a fixed outlet pressure, and you want that version, because it has a much lower pressure loss than the adjustable-pressure versions.

So, with a 60 psi CSV and a pressure switch set to shut the pump off at 70 psi, and a master valve feeding the mainline, you have enough margin of error to get away with 100 psi poly, and to have a pressure relief valve to open at about 80 psi.

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