How do you know what pipe is right for your irrigation application? With so many different options out there, it is easy to be pulled in the wrong direction or take some bad advice that can cost you in the long run. Here is a brief description of the difference between Class and Schedule PVC pipe, what it is used for and it’s best application. First let’s get started with a brief description of PVC pipe so we can cover the basics.
PVC is an abbreviation for Polyvinyl Chloride, the most common plastic in the world. This is a solid pipe that comes in many different sizes and colors. You commonly see it as a white color and readily available at any supply store. This is the most commonly used type of pipe in the industry and is a common household name. What you don’t know is that PVC pipe comes in many different colors and each color serves a very specific function. For this phase of the conversation, we are going to ignore the colors and just concentrate on the different classifications:
- Class PVC – Look at the writing on the side of the pipe and it will either say ‘CL’ or ‘SCH’. ‘CL’ or Class is a form of pipe that is rated for the pressure that it can withstand. Class 200 means that the pipe can withstand 200 PSI (Pounds per square inch). This pipe is very thin, brittle and is not flexible at all. There are 2 main applications that it is applied: (1) In large diameter (Over 1”) and high rating (300+ PSI) for Mainline (pipe that is under constant pressure and is a water source for your irrigation valves). This is the best application for this type of pipe because the high PSI rating and the large diameter make the material less brittle. (2) In small diameter (Under 1”) and low rated (200 PSI) for Lateral line (Pipe that is not under constant pressure and is on the other side of the valve as the mainline. Lateral’s are best described as the pipe that is directly connected to your sprinkler heads). This is the worst application because working with it is difficult and is subject to breaking and sheering. It is use for this application because it is the least expensive pipe to use.
- Schedule PVC - Once again look at the writing on the side of the pipe and it will say ‘SCH’. Schedule PVC is rated by thickness of the wall of the pipe. If you put a class pipe and a schedule pipe next to each other, you will see that the schedule pipe is much thicker than class. This pipe is used in all different diameters for all different applications. The pipe is flexible and does not break easily. The pipe can also be heated up and bent if necessary. This pipe is also more expensive due to the amount of material needed to produce a thicker-walled pipe.
As a consumer, selecting schedule pipe is always a wise decision because it truly is an easier product to work with. If you are looking to save some money on material, you can use class pipe but you will spend your savings on labor trying to work with the material. If you want to learn more about the different colors of PVC, please take the time to read my blog on Color pipe.
Since Class 200 is cheaper I have seen it used to cut corners on mainlines. When combined with under sized pipes to save money and excessive velocity (FPS) Class 200 pipe will suffer from “pipe erosion” which leads to mainline breaks. When one break is repaired another break will quickly appear as the pressurized water finds the next weakest spot. The pipe is soon a patchwork of repairs until entire sections of mainline have to be replaced. Sometimes cheaper is just plain cheap. I highly recommend using Schedule pipe for the mainline and Class pipe for the laterals.
I agree that class 200 has no place in a mainline system. I have seen Class 315 used frequently in Mainline systems and ironically, the wall thickness is comparible to schedule 40 pipe once you get to that rating. Truthfully, if you can use SCH pipe for the entire installation, you will always be better off. Now the industry standard is to use class pipe for laterals because it is not under constant pressure and is substantially less expensive that schedule pipe. What i have discovered is that class pipe is very brittle, can barely be bent and is more vulnerable to sun exposure. All this equates to is that you have to run your trenches straight as an arrow, your skill level has to be such that you understand the limitations and you can’t keep the pipe on the racks for too long. Having worked both in desert areas and in residential where it is mostly tight spaces, I have lost major production when class pipe is on the plans.
I disagree with some of the information in the article. Class pipe is not made from a different PVC material, it is the same material as in Schedule pipe. The difference is in how the wall thickness varies with pipe size. Schedule pipe has a much thicker wall at smaller sizes, but as the pipe diameter increases, the wall thickness of Class pipe actually becomes greater than that of Schedule pipe. This is why designers often switch from Schedule 40 to Class 315 pipe at 2″ size. Sch. 40 pipe at 2″ has a wall thickness of 0.154″ while Cl. 315 pipe at 2″ has a wall thickness of 0.176″. Class 200 PVC pipe actually has a thicker wall than Sch. 40 at sizes above 4″.
The article seems to state that Class 200 pipe is used at high ratings (300+ PSI). Why would you use a pipe with a 200 PSI rating at high pressure? It does not make sense. You would always want to use a pipe that has a higher pressure rating than what you expect to experience in the system. Class 200 PVC pipe is often used for irrigation mainlines in systems where the pipe size is over 3″. This is usually bell & gasket pipe and the fittings are often ductile iron. Schedule 40 PVC pipe is not available in this type and neither is Cl. 315 normally available.
The brittleness of the pipe is not based on it being Class or Schedule type. Thicker walled pipe will be stringer and seem less brittle, but as a whole all PVC pipe is brittle. If you want pipe that is not brittle, look into HDPE. I think that we will see huge growth in the use of HDPE pipe for mainlines in the next few years.
Finally, NEVER heat and bend PVC pipe! I have seen pool installers do this and it is not at all acceptable in an irrigation situation. Heating and bending pipe redistributes the material in the wall of the pipe and leads to thinner and thicker areas. It also cause the pipe to become out of round and therefore unable to be properly installed into a fitting. I do not know of any pipe manufacturer that would condone this practice.
Thank you for your reply. I have received alot of negative feedback from this article mainly because I generalized alot of the criteria i set in place.
I am aware that Class and SCH pipe are the same material and that at 4″, Class 200 becomes thicker than SCH 40. Because of this factor, I revise my statement on the brittle nature of class pipe. I will say that Class 200 pipe that is 1″ or smaller has very thin walls and is more vulnerable to UV breakdown making it less desireable if you order an entire project and then have it sit in the sun for an extended period of time. Also, there is a tendency for the installer to be using pipe sheers that are dull, which cause pipe to shatter.
These are realities of the industry that are easily overlooked by the technical data. I was trying to take a more realistic approach to material, specifically related to personal experience. Unfortunately on paper, the use of Class 200 sounds like the most affordable option but when you put in the nature of the material and the labor it takes to install, Sch 40 really pencils out better.
Class 315 was the recommendation for mainline, Class 200 is not appropriate.
Regading the use of HDPE, I couldn’t agree more. I have shifted my focus on pipe to sleeving so I would hang tight and see how the compression strength of these pipes measures up.