Another Sprinkler System Question

[crokett]

I'm sure this will be one of many. The pipe that comes from my well is 1.25" OD black pipe. It T-s to the presssure tank then comes the pressure guage then comes a reducer to 3/4" copper which is the line to the house. The reducer is a threaded fitting into the fitting for the pressure guage. Is it worth my while to tie the sprinkler in before it reduces? I think it riskier to do it this way, if only because I know I can cut into the coppper. This being plumbing I have visions of much swearing, a wrecked fitting and no water when I try to unscrew the threaded piece.

[Uncle Cracker]

There will be some pressure loss at rated flow if you tie into the smaller pipe, rather than the larger, but the small diameter run is short, so you probably won't notice a difference. Just make sure you up-size the pipe you feed the sprinkler system with for the flow you need, rather than continuing the restriction using the smaller pipe size.

[crokett]

That may be the way to go and simplifies things a lot but...

here is the hookup. The pump comes in from the right. There are enough hose clamps that it would be fairly straight forward to disconnect stuff and add a T to use the larger pipe. The white PVC is to the pressure tank and the copper goes off to the left. If I hooked into the copper it would only be 2-3 feet of copper before I did the tie in and upsized the pipe.

Now there should be a check valve somewhere between the pump and the pressure tank, no? Else the water will just flow back down into the well. Is it possible it is down in the well? I don't see one anywhere, unless the T to the pressure tank is a check valve also. For me to hook this in pump side means I need to move the pressure tank closer to the pump and I need to find that check valve and make sure it stays between the pump and the pressure tank.

[Tom Slick]

I'd hook the irrigation into the copper pipe.
It looks like it is missing the back flow valve and pressure relief valve.
I'd install the check/back flow valve inline right after the pump. If that's not possible I'd install it where the tee for the tank is currently. either way it will keep the tank or main from draining.

I'd remove the bushing and gauge/pressure switch from the current tee and install another tee vertically with a pressure relief sticking up like your switch does now. out of the other part of the tee (horizontal) I'd install another tee horizontal to mount your switch/gauge. the remaining outlet of the tee would be plumbed into your tank.

[Tom Slick]

quick and dirty sketch

[crokett]

Tom,

Thanks for the picture. I agree with you that the backflow preventer should be there but this setup has been working AFIK for 20 years, at least that is what the records I have say. This begs the question, is the pump currently acting as a backflow preventer when it is not on? Or am I missing something else? I know the pressure tank is holding pressure.

[Uncle Cracker]

There is probably a foot valve on your pump, if it's a submersible type. This does the job of a separate check valve. There may also (instead of a foot valve) be a check valve built into the top of the pump. Beyond that, it really doesn't matter where you tie into the feed line, since they're all pressurized, and the pressure switch will react the same no matter what. As for the backflow preventer, from the health standpoint, it protects your drinking water from the possibility of contamination from your sprinkler system, so it's a good idea, if this setup feeds your drinking supply. However, those things, depending on type, can rob you of as much as 15-psi of pressure from your sprinkler main. This is enough to really screw up the proper operation and distribution of your heads. If you add one, use the lowest-pressure-loss type your codes will allow. From lowest to highest loss, the available types are: dual-check, double-check (there's a difference), pressure-type, and reduced-pressure. These are often abbreviated DC, DCV, PVB and RP. It is probable that not all of these are acceptable within your codes or municipality. The RP type is the worst robber of precious PSI's, and the most expensive, but also offer the best level of protection. Hope this helps.

[crokett]

Thanks for the info. I am going to tie into the copper, it just seems easier and already planned on both a ball valve for shutoff and a backflow preventer. Would it be worth it to also install a hose bib or similar after the bp to drain the system?

[Uncle Cracker]

Some sort of drain would be useful at a low point, but not at the BFP. You've got to let gravity do the draining. Also, most BFP's already have petcocks for testing, so it would be a redundancy at that location. You will crack your BFP if it freezes with water in it. It's also a good habit to minimize possible leak sources in a pressurized system, so there's less chance that a dribble can set up a pump cycling problem. A ball valve makes for a better drain valve than a hose bibb.

[crokett]

The BFP will be in the basement, so no chance of it freezing. I realize it will add extra feet of run on the piping but I can route it to get the 24" horizontal run that the BFP will need before it leaves the basement. The BFP would be the low point, or close to it.

[Uncle Cracker]

In order to function properly, most BFP's have to be installed at a level above the highest sprinkler outlet. Your basement aspirations will limit you to either the dual-check or double-check types, and these types are not approved in many jurisdictions, as they have relatively less reliability (from a potential hazard standpoint) than do the types with atmospheric venting. You need to check with your plumbing powers-that-be. It also makes no sense to install a BFP in a manner that renders it less effective. That's just throwing good $$ after bad...

[crokett]

In order to function properly, most BFP's have to be installed at a level above the highest sprinkler outlet.

Uumm... asking a stupid question. Unless it is under pressure water flows downhill. Installing a BFP above the highest sprinkler means it is uphill from the sprinkler system so water won't be flowing back to it. Eactly how is it preventing backflow?

[Uncle Cracker]

PVB and RP backflow preventers must be installed above the protected piping because they have atmospheric vents. These are necessary for the device to have a more positive level of protection (by breaking any possible siphonage potential). If installed below the downstream piping, then gravity would allow water in the piping to bleed out through these vents every time the system shut down. Your basement would then become less habitable.

DC and DCV devices do not have the vents, so they do not require elevation above downstream piping, but also provide a much reduced level of protection, and therefore are not acceptable by most jurisdictions.

[crokett]

PVB and RP backflow preventers must be installed above the protected piping because they have atmospheric vents. These are necessary for the device to have a more positive level of protection (by breaking any possible siphonage potential).

I understand that part, but to my simple brain, having them installed above the protected piping makes their 'more positive level of protection' just a simple law of physics, no? I mean I could install a straight run of pipe above the protected piping and it would do the same thing since water can't flow uphill, unless it is under pressure of course.

Not doubting you, just trying to have this all make sense so I understand it.

[Uncle Cracker]

A straight run of pipe can still allow water to flow back under siphonage conditions (what do you think happens when you siphon water out of an above-ground pool?). By introducing an air break, RP and PVB devices negate this possibility.