A problem with most anti-siphon plastic irrigation valve installations on PVC risers is that if the valve fails, one is usually forced to cut off pieces of the plastic pipes to cement new fittings on so that the new valve can be installed, or the valve body must be sawed in half to remove it from the pipe, destroying any hope of repairing the valve. If the original installation was neatly done with all valves at the same height, the repair job looks bad. Moreover, if the valve was originally installed close to ground level, it may end up below ground after the pipes have been shortened. Here's a way to keep your installations looking neat and easily repairable.
Originally, I considered using PVC union fittings, but they are quite expensive and bulky. I finally settled on an inexpensive solution using expendable parts that can be unscrewed from the valve body and risers.
The first photo in this series (above) shows the original backyard valve installation, with some earth dug away to expose the pipes. The valve on the left has been replaced at least once already, requiring the riser to be cut and material to be spliced on to bring the valve back up to its original height.
Instead of cementing the slip x male pipe thread (MPT) PVC fitting directly to the PVC riser, instead we construct short adapter sections consisting of a slip x female pipe thread (FPT) fitting, short piece of PVC pipe, and slip x MPT fitting. We need two of these adapter sets per anti-siphon valve. Cut the pieces of PVC pipe so that about 1/2 inch of pipe will be exposed between the two fittings once they've been cemented on. Since the slip part of PVC fittings varies between manufacturers, you'll need to measure the depth of the fittings with a small ruler or depth gauge; add the two measurements and add 1/2 inch to determine the length of the PVC pipe pieces. A miter box and miter handsaw or an electric miter saw are very useful for getting uniform, square cuts.
As you can see in the photo, I'm using a scrap piece of 1x2 lumber as a stop so that I get absolutely uniform lengths of PVC pipe. You can use the same trick with a miter box, using a C-clamp to hold the stop in place.
Here are the components of the two adapter sections prior to assembly. The slip x FPT fittings are on the left; the slip x MPT fittings are on the right. The pieces of pipe are Schedule 40 PVC.
Wrap the MPT fittings with 5-6 turns of plumber's Teflon® tape and screw them into the irrigation valve.
De-burr the ends of the PVC pipe pieces and clean all surfaces to be cemented with PVC primer or lacquer thinner.
Using PVC pipe cement (clear or "hot blue"), cement the short sections of pipe into the slip x FPT fittings according to the instructions on the can, making sure the pipes are fully inserted. While the cement is still wet, twist the pipe in the fitting at least a half turn to make sure there are no voids in the cement layer, so the fitting won't leak later.
The glue line doesn't show in this photo, because I happened to use clear PVC cement.
Glue a slip x MPT PVC fitting to the top of each riser.
The first photo shows a riser manifold under construction to handle up to five valves. The lower half of the adapter has been temporarily screwed onto one of the fittings for illustration purposes.
Note that the adapter will add about 3-1/2 to 4 inches to the riser height, so if vertical space is limited where you'll be installing your valves, you'll need to reduce the riser height accordingly before cementing the slip x MPT fitting onto the riser.
The second photo shows how two valves will be mounted side-by-side on the riser manifold. The adapters are dry-fitted only, not glued.
The third photo shows the manifold attached to the supply pipe and placed in the hole where the valve cluster will be installed.
Now you should have a slip x MPT fitting cemented on both the inlet and outlet riser for each valve position. The fittings should be at the same height, as determined with the aid of a carpenter's square, or the outlet pipe should be lying loosely in the trench so that you can freely adjust its height up and down a bit relative to the inlet riser.
Wrap the male threads on each riser with 5-6 turns of Teflon® plumber's tape and screw the lower half of your PVC adapters securely onto the risers.
Apply a generous amount of cement to the slip fittings previously screwed into the valve body and the pipe stubs of the adapters you just installed on the risers. Without delay, push the valve down onto the risers, making sure that the PVC pipe stubs are fully seated in the slip fittings. You won't be able to twist the fittings much, if at all, to distribute the cement in the joints, so having the joints thoroughly wetted by cement is essential for achieving leak-free joints.
Allow the cement to set for 30-60 minutes before pressurizing with water and testing for leaks.
Here's the finished result, a few years later. Only three of the five risers in the manifold are in use; the unused ones are capped and reserved for future use. Should it be necessary to replace one of the valves, one would cut through the PVC pipe in the adapter section in the areas indicated by the red arrows, then unscrew and discard the slip x FPT parts remaining on top of the risers. Also, unscrew and discard the slip x MPT parts remaining in the valve body.
To install a new or repaired valve, purchase two slip x FPT fittings, two slip x MPT fittings, and cut short pieces of Schedule 40 PVC pipe as before. At current prices the materials will cost less than $2. If done correctly, the PVC riser will never need to be cut and spliced and your valve installation will look good as long as you care to keep it and maintain it.
That's it! Thanks for viewing.