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How to Build an Irrigation Valve Manifold Using PVC pipe Fittings

To ease both installation and maintenance many people install their valves in valve manifolds. A Manifold is simply an assembly that lets you attach all your valves in a one area on a common pipe. This gives them easy access for maintenance, prevents them from being lost due to construction or being overgrown. It can cut also down drastically on the cost of wiring.

You can buy a pre-made manifold if you wish. The advantages are: 1. They are made of schedule 80 PVC, heavier than you can normally purchase 2. They are pressure rated so you know what they will handle 3. Really cuts down on the labor. 4. Simple to use. This shows one with the valves already installed.  They are available with valves complete or as do it yourself assemblies.

There are disadvantages to the pre-made manifolds. The primary one is that the dimensions and connections they offer may not fit what you need. The second, though not common, is a situation where you will have non-standard shapes.

Designing and building your own manifold is fairly simple. One consideration before we do anything is: where will it be installed? If it is underground in a valve box, how big a valve box do we have? For example, the standard size is roughly 13” x 20”. If we are using one of these we need to design to fit. If you are not installing in a valve box then we are free to design as we wish. We’ll assume we are using a valve box.

Questions you should know before we start:

  1. How many valves?
  2. Do we want to design for future expansion?
  3. What size pipe?
  4. How big is our valve?

The “how big is our valve” question relates to more than “it fits a 1” pipe.” It also relates to the physical size of the valve. Looking at just one major brand, the width on 1” valves ranges from 3 1/8” to 4”. If you add another brand the smallest size drops to 2 7/8”. What does this mean to you? We need to know beforehand what valve you will use. This gives us our minimum spacing.

Now look at valve types. All valves are designed to have the tops removed. This lets you repair them without removing and replacing the entire valve, which can involve good deal of digging, cutting, gluing, and usually a little cussing.

Some are disassembled using screws. This is pretty straight forward. Some, however, are known as “jar top” valves and have a screw-on top, as its name implies. If you have a jar-top type you need to allow room for fingers to get on each side of the top to grip and remove.

Assume we are using jar top valves and need 4 of them. Each jar top is 3 1/8” wide. So touching edge to edge would give us 12 1/2”. Now we allow 1” between each of them AND 1” on the outside of the two outside valves. This gives us 17 1/2”. Working on the edge of a valve box is difficult enough. We’ll need the full inch. Even if you use the small valves with Phillips head screws allow some working space between them.

Now we know that 4 valves will fit easily into the standard valve box mentioned above. All we need now is rough design and a list of parts. Sketch out your design, paying attention to fittings. Doing so will automatically build the part list.

This tells you that you need 4 Tee’s, 4 couplers, 1 end cap and your main pipe. You run the pipe past the last valve and cap it off to allow for future expansion. Or, if you only need three valves, go ahead and build for four and cap the fourth one. The pipe should be Schedule 40. It will provide the strength needed to handle not only the water pressure but the stress the assembly goes through while being assembled and placed. The connections at the valve depend entirely on the type of valve you purchased. So that sketch translates to:

While most manifolds tend to be of a similar design there are no set restrictions other than system performance. If you need it multi-level, in a square, a cross or whatever, the parts are available. Just build to fit.

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