What Pressure Can a PVC Pipe Withstand?
The pressure rating of a PVC pipe is directly proportional to its wall thickness (schedule) and inversely proportional its nominal size. Small-diameter PVC pipes can withstand more pressure than big-diameter pipes, while schedule 80 pipes can handle more pressure than schedule 40 pipes.
In short, the pressure rating of PVC pipes decreases with increase in nominal size while it increases with increase in wall thickness (schedule). The pressure rating also decreases with increase in temperature.
Unlike metal pipes, PVC pipes cannot withstand very high pressure but small-diameter PVC pipes handle pressure better than large pipes. For example, ¼-inch schedule 80 PVC pipe can handle 1130 psi while a 6-inch pipe will only handle 280 psi.
Schedule 80 PVC pipes are stronger than schedule 40 pipes due to their thick walls. As a result, schedule 80 pipes will handle more pressure compared to schedule 40. For example a 2-inch schedule 80 pipe will handle 400 psi of pressure while a similar size schedule 40 pipe will handle 280 psi.
The pressure rating for schedule 40 PVC pipes just like schedule 80 PVC pipes decreases with increase in nominal pipe size. For example, a 1-inch pipe has a pressure rating of 450 psi while a 6-inch pipe has a pressure rating of 180 psi.
Schedule 40 and 80 PVC Pipes Pressure Rating Vs Nominal Size Chart
|Nominal Pipe Size (Inches)||Schedule 80 Max W.P (PSI)||Schedule 40 Max W.P (PSI)|
PVC pipes and especially schedule 40 pipes are not very good under pressure especially with compressed air or natural gas. The only type of PVC pipe allowed to be used for high pressure applications like transportation of natural gas is modified PVC pipes (PVC-HI).
Schedule 40 PVC pipe is the best pipe for plumbing. In United States, flexible PVC pipes (plasticized) are preferred for their flexibility while in Europe rigid PVC (UPVC) is the pipe of choice. Chlorinated PVC pipes (CPVC) are best used for portable water, both cold and very hot.
Note that PVC pipes have a maximum operating pressure and a burst pressure. The minimum operating pressure is the pressure which shouldn’t be exceeded when using the pipe while the burst pressure is the pressure at which the pipe will burst open.
There is a healthy margin between the maximum operating pressure and the burst pressure for safety reasons. For example, the maximum operating pressure of a 2-inch schedule 40 PVC pipe is 280 psi while its burst pressure is 890 psi.
Schedule 40 vs 80 PVC Pipes
When we talk about the size of PVC pipes, we could be talking about the nominal pipe size (NPS) or the wall thickness. PVC pipes do not have the same size of wall thickness.
To start with, wall thickness in pipes is known as schedule. We have two main types of schedules; schedule 40 and schedule 80 PVC pipes.
The schedule of pipe simply indicates how thick a pipe’s walls are. Schedule 80 PVC pipes have thicker walls than schedule 40 PVC pipes.
Apart from that, the wall thickness of PVC pipes increases with increase in nominal size. For example, the wall thickness of a 2-inch schedule 40 PVC pipe is 0.154 inches, while that of a similar size of a schedule 80 pipe is 0.218 inches.
As I have mentioned, the wall thickness increases with increase in the nominal size of the pipe. For example, the wall thickness of a 6-inch schedule 40 PVC pipe is 0.280 inches, while that of a similar size schedule 80 pipe is 0.432 inches.
The extra wall thickness of schedule 80 PVC pipes over schedule 40 pipes allows them to withstand more pressure. For example, a 1/2-inch schedule 40 pipe will handle 600 psi while a similar size of schedule 80 pipe will handle 850 psi of pressure.
Schedule 40 PVC pipes are mostly used in residential and commercial plumbing especially in the installation of drain lines. As you may already know, drain lines are usually not pressurized which makes schedule 40 PVC pipes a good choice.
Schedule 40 PVC pipes can also be used outdoors in irrigation systems or sprinkler systems. The pressure of water flowing to your house is usually between 40 and 60 psi and schedule 40 PVC pipes will comfortably handle that pressure.
Schedule 80 PVC pipes are mostly used in manufacturing and chemical industries where fluids are transported at high pressures. Having said that, nothing should stop you from using schedule 80 PVC pipes for your DIY activities if you so wishes.
It is important to remember that schedule 40 and 80 PVC pipes of the same nominal size have different inside diameters but similar outside diameter. As such, you can connect the 2 pipes together as long as the pressure rating of the schedule 40 pipe or fitting is higher than the pressure of the fluid being transported.
PVC Pipes Pressure Rating vs Temperature
|Temperature (Degrees Fahrenheit)||PVC De-rating Factor||CPVC De-rating Factor|
As I had mentioned earlier, the pressure rating of PVC pipes decreases as temperature increases. This is because the pipes are stiff at low temperatures and flexible/softer at high temperatures.
At 73 degrees Fahrenheit, PVC pipes have a de-rating factor of 1. However, as the temperature increases, the de-rating factor decreases. For example, the de-rating factor of PVC pipes at 120 degrees Fahrenheit is 0.40.
If for instance you want to calculate the maximum operating pressure of a 6-inch schedule 40 PVC pipe at 120 degrees Fahrenheit, you simply multiply 180 psi by 0.4 to get 72 psi.
The limitation of ordinary PVC pipes under high temperature is the reason why there is a special PVC pipe known as CPVC, which is basically PVC which has undergone a chlorination process to increases its chlorine content.
The result of the chlorination process is that CPVC pipes can withstand a higher temperature before softening compared to ordinary PVC pipes.
To be precise, ordinary PVC pipes will start softening at temperatures above 140 degrees Fahrenheit while CPVC pipes can handle temperature as high as 200 degrees Fahrenheit before softening.
At 73 degrees Fahrenheit, both PVC and CPVC will have a de-rating factor of 1. However, as temperature increases, CPVC maintains its pressure way better than PVC.
As example, let us look at what the working pressure of both PVC and PVC will be for a 10-inch schedule 80 pipe at 130 degrees Fahrenheit.
- At 1300 F, PVC has a de-rating factor of 0.31 and hence (230 psi x 0.31) = 71.3 psi.
- At 1300 F, CPVC has a de-rating factor of 0.57 and hence (230 psi x 0.57) = 133.1 psi.
From the above explanation, it is clear that if you need a pipe that can handle hot fluids at high temperatures then CPCV pipe is the pipe to consider, especially CPVC schedule 80 pipe.
Apart from being excellent for transporting hot and cold water under pressure, CPVC pipes are also available in both nominal pipe size and copper tubing size (CTS).
And basically that is the relationship between PVC pipe sizes and their pressure rating. I hope that this guide was of benefit to you.