Tag Archives: PVC pipe installation

Jun 28 2012

Pipe Dreams? Or PVC Pipe dreams? There is a difference.


If you don’t know the difference we can’t help you here. This is not that kind of a blog. If you have nightmares about figuring out which pipe to use for your irrigation then we can help.

PVC stands for polyvinyl chloride. PVC is easier to say. PVC pipe accounts for about two thirds of the water distribution market, including drinking, irrigation and waste. So far the material has been found to be inert, meaning it doesn’t absorb or release harmful chemicals. Unless you burn it. Don’t sniff burning PVC.  It’s no fun, painful and the smoke can be hazardous.

The most common question we get is a two-parter: what size pipe should I use and what kind: Schedule 40 or Class 200? Knowing the differences can help you create an efficient system.

Remember the old “a picture is worth a thousand words” quote? I’ll give you a picture now and you can decide if you want to skip the other 476 words.

Let’s talk about Schedule 40 pipe first. It is the simplest. Schedule XX designates the wall thickness at a certain size. For example, a 1” pipe in schedule 40 has a wall thickness of .133”; schedule 80 has a wall thickness of .179”. Higher schedule = thicker wall.

You will care about this later. It does get more interesting, hopefully.

“Class” pipe is different and the original definitions go back to steam boilers. We’ll skip ahead. Class 200 pipe, the most common class pipe used in irrigation, is rated for 200 pounds per square inch pressure (psi) and has a wall thickness of .063” for a 1” pipe. Notice that is a lot thinner than schedule 40. This is about to become very important. Schedule 40, in comparison, is rated for 450 psi. This is not as important.

The average irrigation system is designed for about 30 to 50 psi. Plenty of safety factor built in. It is not, however, as much as you think. A poorly designed system can experience water hammer and a 60psi line can experience frequent surges of pressure up to about 170 psi. Still within safety range.

Now we can get into the “why do we care” part.  Everything in irrigation ties into gallons per minute. Your spray head puts out a certain number of gallons per minute (gpm). Your design revolves around it. If you have 13 gpm you can put six 2 gpm heads on that zone. Or four 2gpm and four 1 gpm. (Never design to the absolute max gpm.)

Look at the cross section of ¾” and 1” pipe both in schedule 40 and class 200. Check the comparative flows in the picture above. This difference in flow can make a big difference in how you design your zones. There are friction loss/flow charts available to help you.

So what do you choose? The rule of thumb is to use schedule 40 for the main line. Run it from the water meter, through the backflow and to the valves. Then use class 200 for the laterals, or after the valves.

Why schedule 40 when it allows fewer gallons per minute? Because the thick wall makes it tougher, harder to break. Your main is under constant pressure; the laterals are under pressure only when they are active and it is an open-end system. Before real pressure can build in your laterals the water is shooting out the sprays, keeping pressure down. Schedule 40 is more resistant to shovels (its sworn enemy), tent stakes, car tires, kids, dogs and other puncture/crack pressures.

There are exceptions to everything. There are situations where an entire system should be done in class 200 pipes. Same for schedule 40.  Now that you know the difference you can make a more informed decision and start dreaming about better things, like a 1973 Norton Commando.

Mar 16 2012

The Right Way to Assemble and Glue PVC Pipe


There are many ways to glue PVC pipe and a number of solvents.  The bright side is most of them will work. The down side is many of them won’t, wasting time and money, or only appear to work until the pipe is long buried. Then it becomes expensive.

We are going to discuss measuring, fitting and gluing pipe. The premise is that if you do it correctly you only do it once. Not to mention limiting trips to the hardware store and controlling blood pressure.

Before we do anything else, there are two warnings. One on safety, one on product performance.

  • Folks, these are harsh chemicals. Don’t get them on your skin. Definitely don’t get them in your eyes. No breathing fumes. Make sure you have plenty of ventilation, as in ‘do it outside’. Wear gloves. Wear eye protection. Care to guess what the cement does to plastic contacts or your expensive glasses?
  • There is such a thing as too much glue. This is not Elmer’s Paste. If you put too much cement on and it has a chance to puddle it can and will eat through the pipe or fitting. Now you have a hole in the fitting. Also, too much glue when attaching valves can drip into the valve body and cause failure.

First, get these things together:

  • Rags
  • Primer and cement
  • Something to put the pipe on while you cut (sawhorse, cinder block, table, etc.)
  • Gloves
  • Hacksaw
  • Marker or crayon
  • Rough file or course sandpaper

Optional but you should have

  • Miter box
  • Pipe cutter, preferably ratcheting type though standard will work fine.
  • Hammer/Channel Lock pliers

Measuring is the shortest part of this paper. Remember that you have to include the length of pipe that goes into the fitting and the length of the fitting. Say you have a 10’ section from corner to corner.  The fittings add length. You need to figure out how short to cut the pipe so you can add the fittings and still get 10’.  How far does the pipe go into the fitting?  Depends. Depends on the cut, the pipe, your strength.  There is a stop designed into the fitting. How far in is it? To find out, take the pipe and fitting, get them wet with water only, and push the pipe into the fitting with firm but not killer force. The water makes it easier to slide them together. Now take a pencil and mark the pipe at the edge of the fitting. Twist the pipe back out. The distance from that mark to the end of your pipe is your glue area. This can vary depending on fittings and pipe size.  Measure everything twice. Write it down.

Cutting the pipe is more important that people realize. The cut should be square and smooth.   If you don’t cut it square the short end will not make complete contact with the inside of the fitting and will not bond as it should. It helps to use a miter box, if you can, or good ratcheting cutters. Take your time. It will help avoid problems later.

Ideally the end of the pipe should be smooth with tapered edges. Now I know you don’t hear many people talking about tapering a PVC pipe edge. You’ve probably never seen it and I know many professionals that have never even heard of it. However, we’re discussing the correct way to do this. You can bring in the shortcuts when I’m not looking. If you have a simple square cut pipe it has a tendency to push the cement ahead of it, as in the drawing. A smooth pipe with an edge taper lets the cement flow between the two. So take your file, file off the burrs that are left from the cutting, if any, and add a quick taper to the end. At the very least use sand paper to smooth the edges and take off any burrs.

On to fittings.  Once you have your pipe cut do a practice assembly. We do this to make sure we don’t glue the elbow on facing the wrong direction. Lay the pipe out along the trenches. Put the elbows, Tee’s and 45’s on just as if you were putting it in the trench. Once you are sure it is correct draw a line on the fitting and pipe with a marker or crayon. This will help line it up for you when the cement is on and drying fast.

Ok. Pipes are cut, fittings are ready. Now time for primer and glue. First I’d like to clarify one thing. It’s not really glue or cement. It’s a solvent. The solvent basically melts the PVC. When two pieces of PVC are joined using PVC cement the plastic melts, molecules blend, and it re-solidifies to a single unit.  That’s a gross simplification of what happens but its close enough.  When the cement is through and the PVC has re-solidified it is now the strongest piece. If you do it right the fitting or pipe will break long before the joint.

The first thing you do is make sure the pipes and fittings are dry. There are some cements that don’t need primer and will work with a wet pipe but we tend to avoid them. First, using primer gives us a last chance to check the pipe. You’d be surprised how often a small crack will hide until the primer hits it. . The other reason is that special cement tends to set FAST. Real fast.  No room for error or hesitation. Why ask for trouble?

Now prime both the pipe and the fitting. Use just enough to do the job. Too much doesn’t gain you anything. Using the included dauber wipe the glue area of the pipe and the glue area of the fitting with primer. Since it’s purple it’s easy to keep track. By the way, it stains everything so be careful. Primer removes dirt and grease and preps the PVC. When PVC is formed it has a hard, clear coating on it. This is resistant to the cement. Primer removes the coating, exposing the PVC.

Now apply the cement to both pieces. Do the fitting first. Since the cement is inside you can lay it down for a moment while you coat the pipe. Once both are done push the pipe into the fitting, turning about ¼ to ½ turn as you go. This makes sure the cement spreads evenly. Hold it together for about 15 to 30 seconds. Because of the chemical reaction and the way the fittings are formed there is a tendency for push back. The pipe will want to come out so hold until is sets.  If you’ve done everything correctly you can look around the edge of the fitting and see a little glue bead that has been push out by the fitting. It should be continuous. A gap might mean a pinhole leak later. Wipe off any excess cement.

I know. I didn’t say what you did with the pliers or hammer. That’s ok. They are always good to have.

That’s it. Doing takes far less time than reading about it. Doing it correctly doesn’t add any time and sure can save you a headache in the future.

Mar 5 2012

Teflon Tape and How To Use It


Teflon Pipe TapeTeflon® tape (polytetrafluoroethylene, or PTFE), AKA plumber’s tape, is a thin film used to seal pipe threads. The tape is durable, flexible, and fills in the minor imperfections in the threads to seal leaks.

To use, hold one end of the tape against at the start of the pipe threads/end of pipe and start wrapping opposite of the direction of the threads, keeping the tape flat. Pull the tape Wrapping Pipe with Teflon Tapetightly into the threads but not so tightly that the threads cut through. Keep going in a flat uniform manner until you come to the ends of the threads/pipe. Now thread the pipe in carefully and you’ll have a good seal.

You want more than one layer but generally not more than three or four. If you are using drastically different materials, such as copper or brass to PVC, you may need extra but that is unlikely. Too much tape is as bad as too little. It will prevent a good seal. With the proper amount the pipe should thread together smoothly, sealing all gaps in the thread.

When do you not use plumber’s tape?

This tape is only effective on tapered threads as it uses compression to form the seal. Fortunately, the vast majority of the connections you make in irrigation will be with National Pipe Thread Tapered Thread, or NPT, and this tape will work well.

Many will tell you that brass to brass fittings are self sealing. In one manner they are but it takes an experienced professional to know which ones will work. You risk a leak if you are not sure you have the correct condition. Tape is cheap insurance. Brass fitting threads also tend to be extra sharp, especially on the smaller pieces, and may cut through the tape and ruin the seal. In this extra care is needed. In extreme cases you might need pipe dope but that is rare. The general connection involving brass in an irrigation system is with the backflow. Plumbers tape should work just fine there.