PVC Pipe Sizing: A Quick Guide for Effective Project Planning

Knowing the materials you’re using makes planning and executing a project more manageable. This also applies to polyvinyl chloride (PVC) pipes.

According to a research review on the primary causes of water pipe failure, the pipes themselves are crucial in ensuring sustainability in water distribution. Moreover, a study from the International Journal of Engineering and Research Technology (IJERT) considers pipes as one of two main factors that cause piping-related problems.

All this points to one thing: proper pipe selection.

Drawing on our experience in the field, we consider pipe sizes and dimensions critical for construction, sewage, or plumbing projects. The wrong choice of pipe size can lead to issues and malfunctions that may deter the smooth progress of your project.

This guide explains PVC pipe sizing based on trade measurements, applications, and other project considerations.

Understanding PVC Pipe Sizes

Selecting the best one from various PVC pipe sizes and specifications is more complex than you think. You can’t simply lay a pipe with one end facing toward you and use your tape measure to determine its size. Doing this will only give you the OD or outer diameter of the pipe, which does not equal the pipe size.

You see, PVC pipes are sized based on a nominal system. This means the measurements (nominal pipe size or NPS) are based on structure rather than the numbers on a tape measure.

You also need to consider the thickness of the pipe’s wall. This is indicated by the pipe schedules (e.g., Schedule 40, Schedule 80, etc.). The higher the pipe schedule, the thicker the wall is.

Selecting the Right Pipe Size

Choosing the correct pipe size depends on several factors, including flow rate, pressure, and intended use. You need to consider all these to determine the best pipe to use for every situation.

Plumbing

Drain lines, water supply lines, and vent stacks require different pipe sizes. This will depend on the public water system fixtures and the local building codes. However, commercial buildings generally require bigger pipes compared to residential structures.

If you’re connecting a residential water supply from your city’s main pipeline, the size of pipes you need to use should be between 3/4 to 1 inch. Opt for ¾-inch supply pipes and 1/2-inch ones for the individual plumbing components.

If you’re working on a building with more than one story, you will need to account for the drop in water pressure as you go higher up. This is around half a pound per square inch (psi) for every foot of height your pipe goes above the main water supply.

In other words, you’ll need to use bigger pipes when running new lines to the second or third floors than what you would use in the basement or ground floor.

Irrigation

Your choice of pipe size and dimension also affects the water pressure and flow rate.

Pipes for irrigation systems in golf courses and farms should match the flow rate of the sprinkler and drip systems.

The higher the flow rate required, the larger the pipes should be.

All types of PVC water pipes have inherently rough internal surfaces, which reduces water pressure (known as head loss). If the water pressure is low, the sprinkler heads in your irrigation system may not work as they should.

If you have long pipes and/or many sprinkler heads, you will need to use larger-sized PVC pipes to maintain the required pressure.

Construction

PVC pipes are used in construction not only for plumbing and drainage but also for electrical systems. The pipes act as conduits for electrical components, protecting cables and connections against the elements. Therefore, choosing the right pipe size and dimension for such projects will primarily depend on the specific application.

For example, you may opt for rigid PVC pipes as electrical conduits. These pipes are watertight and bendable, making them ideal for electrical installations. They are also appropriate for corrosive environments as long as it is allowed by the local building code.

Additional Considerations

Aside from the application, you must consider a few other things when choosing the appropriate pipe NPS and schedule for your project. This includes:

Pressure Rating

The pressure rating is the maximum pressure allowed for a pipe. Below is a rundown of the pressure ratings for various sizes of PVC pipes:

As illustrated in the table, the pressure rating decreases as the pipe becomes bigger. Schedule 80 pipes also have a higher pressure rating than the ones rated at Schedule 40 because they have thicker walls.

Temperature

Note that PVC pipes can also be de-rated based on the temperature upon installation. The hotter it is, the lower the pressure rating becomes.

Here’s a quick summary of the de-rating factor for different operational temperatures:

To calculate the de-rated pipe pressure, multiply the assigned maximum working pressure (psi) according to the pipe’s nominal size and schedule by the assigned de-rating factor in the table above for the given temperature.

So, if you want to get the maximum working pressure of a 1-inch Schedule 40 pipe at 100 degrees Fahrenheit, you need to calculate it like this:

450 psi X 0.62 = 279 psi maximum at 100 degrees

If you’re using pipes for hot water distribution, consider whether the pipe you choose can handle the liquid’s peak temperature. To avoid damage, always follow the manufacturer’s recommendations for the best temperature for PVC pipes.

Chemical Resistance

PVC is resistant to many oils, fats, alcohol, and aromatic-free petrol. It can also withstand most corroding agents, particularly salts, alkalis, and inorganic acids.

However, it can be weak against ketones, ethers, esters, and chlorinated hydrocarbons because it absorbs these chemicals, leading to swelling. When this happens, its tensile strength drops.

To ensure durability and longevity, you must factor in the pipes’ potential chemical exposure. Always refer to relevant charts and guidelines for more information.

Below is a table of the ideal pipe sizes and dimensions based on different applications:

Note that this guide is only an example of the appropriate pipe size selection for common projects. Always consult local building codes and manufacturer recommendations for your next project.

Getting the Right Size for the Job

Selecting the most appropriate PVC pipe sizes for specific applications is crucial to the success of your projects. Know the right nominal size and schedule for various applications and consider temperature, pressure rating, and chemical resistance with the help of this guide.

Here at Polyfab, we offer not only high-quality PVC and HDPE pipes for various applications but also guidance to help our clients do their best work. Make the right choice today.