How well will PEX withstand the increased back pressure from a CSV1A?

[Tubby]

The submersible pump connects to PEX (5106 160psi @73), which connects to the main PVC line (all inside the spring house). I am not concerned about the PVC, just the PEX. The switch is set to 40/60. See fittings in photos.

With a CSV installed, how well will the PEX and its fittings be able to withstand the increased back pressure during and after the slow 1gpm filling of the pressure tank?

The pump is:
SHUR-DRI
SD-A202-02
3/4HP, 10GPM 2 WIRE
230V 60Hz 1PH
Code: 001J09H

I have not been able to find a pump chart for this pump, but I did find one (https://assets.unilogcorp.com/187/ITEM/DOC/STAR_WATER_SYSTEMS_100304387_Catalog.pdf) that rates a similar pump at 162psi max pressure. Again, the PEX is rated at 160psi.

I am not sure how to estimate the "static water level." The pump sits in <2 feet of water, and the water line rises upward about 24 feet before leveling off.

Sorry if I asked about this before, but I did not have as much data.

 

[Reach4]

A 1/2 HP 10 gpm pump would probably have been a better choice.
A 10 gpm 3/4 pump with zero gpm will produce about 160 psi pressure, and at 1 gpm, the pressure will be just a little lower.

That 160 psi for pex is an operating pressure. The burst pressure is much higher.

So you would be operating just below the max at the pump, which is where the highest pressure is.

One more thing, you should have your pump in a flow inducer. You can search for that using the search box above.

 

[Sponsor]

 

[Tubby]

Thank you. That does not seem like much of a safety margin. I do not know whether PEX psi ratings are conservative or strict, and whether the fittings would be stronger or weaker than the tubing.

I also wonder how long the high back pressure will persist. After the pump shuts off, what happens to that back pressure? Does some of it bleed through the CSV and into the pressure tank? I have not been able to find info about this on the CSV site.

I was hoping not to have to make changes inside the spring house until it's time to get a new pump. Then I will have the installer use only PVC. This would also be the time to add a flow inducer; but note that the pump has been going for over 16 years without one.

 

[Reach4]

When the pump is off, the pressure at the output of the pump is the same as the cutoff pressure, plus the "head" between the pressure switch and the surface of the water. For easy computing, each foot of vertical head is 1/2 psi, or for more precise computing, 0.43 psi per foot.

So with 20 ft altitude difference between the 40/60 pressure switch and the surface of the water, then less than 70 psi.

 

[Rim Country Plumbing Co.]

As Reach4 noted, the 160psi on PEX is a continuous operating rating with a big safety factor built in - burst pressures are several times higher, so brief deadhead spikes won't hurt it. Once the pump shuts off, pressure at the pump drops back toward the switch cutoff plus the static head, so the peak only exists while the pump is running against the CSV. If the tight margin still bothers you, a pressure relief valve at the well head is cheap insurance.

 

[KlamathFallsPlumbing]

The 160 psi rating on your PEX is its continuous operating pressure at 73 degrees, while the burst rating is several times higher, so short excursions near the top of the pump curve are well within what the pipe can handle. The CSV1A also has a built-in pressure relief that opens around 175 psi, which caps how high the back pressure can climb in the first place. Where people get in trouble is sustained pressure well above the rating combined with hot water, since PEX ratings drop as temperature rises, but that is not your situation here. Keep an eye on the pressure gauge when the pump runs against a nearly closed valve and you will see it stays comfortably under the relief point.

 

[Fitter30]

Any pipe has at least two ratings working and burst. Under working pex 180 lbs @ 73°. Hot 100 lbs @ 180° also pex has a rating for chlorine resistance. Burst could be up to 700-800 lbs. Look up your brand and size. If ou can't fins te info can the company.

 

[Tubby]

As Reach4 noted, the 160psi on PEX is a continuous operating rating with a big safety factor built in - burst pressures are several times higher, so brief deadhead spikes won't hurt it. Once the pump shuts off, pressure at the pump drops back toward the switch cutoff plus the static head, so the peak only exists while the pump is running against the CSV. If the tight margin still bothers you, a pressure relief valve at the well head is cheap insurance.

The "big safety factor" is good to hear.

I also have the benefit of being able to crawl into the spring house and watch the action.