I see a short list of code violations but before we go any further, what is the diameter of the copper pipe from the PVC tee to the main shutoff valve (valve with red handle)??

It's 3/4" copper.

The PVC pipe from the meter to the house location is not a problem other than it is probably undersized, but we cannot determine the correct size without having a list of all plumbing fixtures in the house and the number of irrigation heads and the GPM rate for each head.

Schedule 40 PVC pipe is rated for a maximum working temperature of 73degF and a maximum pressure of 450psi. Schedule 80 has a max temp of 73 and a max pressure of 630psi so the line pressure from the municipal main down to the house is okay.

The house is 25' lower than the meter box at the street so there is a 10.85psi increase in pressure at the house from VSH (vertical static head).

The TEE to the irrigation system is also ok, but irrigation systems are not governed by code and the code requires that there MUST BE a backflow preventer immediately after the TEE to isolate the irrigation system from the house potable water supply.

The irrigation "main water shutoff" valve may be placed at any convenient point between the backflow preventer and the air gap.

The supply line to the irrigation system must also rise vertically until it reaches an elevation no less than 6" higher than the elevation of the highest irrigation head (when the head is extended to operating position) and there MUST BE an "Air Gap" on the top of the riser.

Female threaded PVC fittings may be used on the irrigation system however both the IRC (International Residential Code) & the UPC (Uniform Plumbing Code) prohibit any female threaded PVC fittings. For the house water supply when using IPS male & female threads to transition from PVC to another type of pipe you must use Male PVC adapters.

The red handled valve below the pressure regulator is a "Gate valve". That is the house "Main Water shutoff valve". Code requires that to be a "Full Bore Valve" so a gate valve or ball valve would be the correct valve.

The PRV (pressure reducing valve)is intended to protect the pipe & fixtures in your house. With your vertical drop from the meter and the irrigation system on the same line that is the correct location for your PRV however I don't think your valve is installed correctly. They do make some prv's for vertical mount and there are even some that are made for "All Position" but the PRV shown there appears to be one that is intended for a horizontal mount. Also note the two round discs on the right hand side of your PRV. Those are caps that cover internal sediment screens. When a PRV is mounted horizontally it must be mounted high enough to allow removing those caps to clean the screens.

The large nut on the bottom end of your PRV body is a compression nut, and there is a flange connection under that nut. The purpose of that nut is to serve as a union to permit removing the valve for service.

Note the yellow handle on the hose bibb. That should not be yellow. You may use any other color, but the plumbing codes specifically say that yellow indicates "Non-Potable water".

Now in regards to your concerns about soldering.

1. Begin by soldering all copper pipes & fittings, then after they have cooled to touch you can make the final connections with the PVC.

2.Your hose bibb is probably mounted on the low end of your water system. Close the main water shutoff valve (red handled gate valve)and open the hose bibb. That will allow the water in the house to drain out. You should also open the cold water faucetts in the kitchen and bathrooms to vent air into the lines to insure they drain correctly.

I would then disconnect the nut on the bottom end of your PRV and cut the pipe between the top of the PRV and the hose bibb so you can remove the PRV for now.

Make sure the hose bibb is open and heat the TEE where it connects to the stub from the house. While heating the tee grip the hose bibb with a pair of channel locks and you should be able to pull it off the stub from the house.

Once you have the tee removed, heat the end of the stub and both quickly & carefully wipe the end of the stub to remove as much excess solder as you can. What your looking for is a light film of solder on the copper as if it is copper plated, but no beads of solder that will make attaching your new fitting difficult. (The light film of solder plating on the pipe will actually make soldering easier later).

I looked at the second photo you have on your photobucket and it appears that your existing hose bibb is soldered on. When you re-assemble this I would suggest you put a copper female thread adapter on the tee. You could then easily screw in a new hose bibb, and in future if you have need to change it, it would again be easy to screw one off and screw another on.

Now regarding your reluctance to solder pipes that might have water in them.

The reason most ppl have problems soldering pipe with water in it is because they simply do not understand the physical characteristis of water.

When water flashes to steam it expands to 12 to the third power or in simple terms, one cubic inch of water will expand to one cubic foot of steam and both water & steam are not compressible, so when the water flashes to steam it fills the pipe and the excess steam pushes out through the solder joint preventing the solder from entering.

Don't underestimate even a few drops of water in the pipe. When it flashes to steam one teaspoon of water produces 2.5gallons of steam and 1 gallon will of steam would fill 98' of 1/2" pipe or 43' of 3/4". As you can see, it would only take a few drops to flash to steam and make soldering impossible. The secret it so first drain the line as much as possible, then vent the line from both ends if possible by opening faucetts or valves. In this case the line will be open to the male thread adapter so soldering should not be a problem.

See annotated copy of your photo below:

Thank you so much lazypup. That was anything but a lazy reply...

I understood most of what you suggested except for the (1)backflow preventer (2)vacuum breaker (3)air gap. I understand that backflow preventer is a device you can buy that lets water flow only one way (is that the same as an anti-syphon valve?) But what is the air gap? And is the vacuum breaker yet a third device/contraption?

I’m not sure about the size of the PVC pipe coming from the street (I mentioned this was a new house but we have not moved in yet and it is some distance from where we live -- so I cannot easily go and take a look). However looking at the picture, it may be a 1” PVC coming from the street and a 1" going out to the irrigation.

In any case, what if I replaced everything with the following setup?

{{gwi:2024790}}

Xmm... the flow in the vacuum breaker is reversed. It needs to go the other way.

So is the pressure reducer shown here installed incorrectly (the valve is horizontal and the valve seems to have cleaning ports).

http://www.diynetwork.com/how-to/how-to-install-a-pressure-reducing-valve/index.html#step1

There seems to be almost infinite advice on the web on how to install a sprinkler system and the trivia of circuits and GPM calculations but few explanations of the seemingly more mysterious part: backflow prevention devices.

This typical Watts pressure reducing valve below looks very similar to mine and the installation instructions claim it can be mounted either horizontally or vertically, or even inverted! which raises the legitimate question: How does the debris stay in the strainer for cleaning?

http://media2.wattswater.com/1910200.pdf

I'm trying to sort this out because seems to me vertical installation would be simpler in my outdoor setup (less pipe exposed to freezing, sure this is in N California but I still need to plan for the occasional 26F night every few years or so).

Hi You may want to give some thought to installing a hose bib between the main shut off and the regulator. Use for high pressure wash downs. As far as coolder weather maybe wrapping the pipe with insulation and when done with the install, box the system in, sort of like a cabinet with doors for access.
Good Luck Woodbutcher