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My lawn sprinkler pressure vacuum breaker cracked over winter so I'm trying to replace it.

There are threaded part's of piping and what seems like welded parts.

All of the piping is metal and no matter how long I hold a torch to the fittings that seem welded they just won't come apart, or even budge.

I've never worked with piping before and my research shows people holding a torch to the welded areas and then being able to pull the piping apart (using quite a bit of force).

Is it possible it's not welded and I need to take a different approach? Do I need to just cut the lines and replace them?

EDIT: Here's a pic, the main fitting I'm working on is the bottom one headed into the house that has the adapter between pipe sizes.

enter image description here

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  • It would help if you provide some pictures of what the joint looks like. With a picture of the joint that is welded, we can better provide an answer – Programmer66 Apr 30 '20 at 0:24
  • pressure and vacuum are mutually exclusive ... the device is a vacuum breaker – jsotola Apr 30 '20 at 0:32
  • did you drain the water? – jsotola Apr 30 '20 at 0:45
  • Yes the water has been drained, although there does seem to have some trapped water because there are small drips coming through the crack in the shutoff valve on the bottom – tamato Apr 30 '20 at 1:06
  • The lower valve is in the "open" position; Is water shut off somewhere else ? – blacksmith37 Apr 30 '20 at 17:13
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I pull sweated joints all the time copper is flexible enough to repair. First I use MAPP gas it is hotter than propane propane will work for most residential sizes but mapp works well. The second is all the water needs to be drained a small amount of water will prevent the joint / solder from getting hot enough to become molten. I will start on one side and heat until the copper is red hot (in direct sun red hot can be at the melting point for copper) then I swing to the opposite side and hit it usually it will release in 2-3 seconds if not moving back and forth a couple of times may be needed watch out for your siding you don’t want to scorch that I will put a heat blanket there to prevent scorching or solder splatter.

When you reassemble super clean and flux parts as with some solder they will need to get hot to go back together, once back together lay a bead of non lead solder on the lap joint and move the torch from the joint inward and this draws the solder in I usually do this on each side then inspect for pin holes prior to turning the water back on. Rap the new vacuum breaker in a wet towel and make sure not to heat it up or the new one could be ruined.

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  • FYI : Even in the backwoods of E TX, Simple anti siphon valves like this one have not been permitted for 20 years. If you replace it , a more expensive ,complicated one is required. – blacksmith37 Apr 30 '20 at 19:10
  • There is some water still in the lines, even though it was attempted to be drained. If the torch is left on the pipes for long enough (about 5 minutes) some water comes out the crack. Seems I need a more reliable way to ensure all of the water is out. – tamato Apr 30 '20 at 19:27
  • If you still have water that is a problem, when I do repairs to a system that has water in the pipes I take white bread no crust and pack it in each end of the pipe to stop the water , solder then turn the water on and flush the bread out (remove any airators or the bread will plug them) but the bread comes out easily and no pin hole leaks. If your supply is slightly leaking there are 2 ways to proceed a dry ice or Co2 freeze to block the water flow or cut the pipe , re assembly may be tricky to get the water out of the pipe and sweat a new valve in so you can turn it off or work really fast – Ed Beal Apr 30 '20 at 22:25
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There appears to be only two sweat joints in your picture at noted in my picture of your piping. It would be difficult to sweat these joints and remove the pipes and valves as there is no leeway to put them apart.
From your edited question and comment, it seems that you are trying to replace the shutoff valve at the bottom and not the vacuum breaker at the top.
Since the bottom valve is the shutoff to the main, you would have to cut off the water to the house to replace this valve.
You can try shutting the water off and draining the water out of the pipes. Sweat the bottom sweat joint, when the solder is softened, pull hard on the fixture and it just might have enough give pull the elbow off the pipe coming out of the wall.

After the valve is replaced, I would add a union on the pipe that goes into the wall or on the down pipe going to the sprinkler.

In the worst case, since you are replacing the valve, just cut the valve in the middle and unscrew each end from the nipples.

enter image description here

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