Using and Understanding PVC Pipe and Fittings
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If you are even a little bit familiar with the irrigation industry, you probably already know there are no set industry standards as far as flexible poly tubing and fitting sizes are concerned. Although PVC is standardized, in its industry, it is still confusing when sizing or matching components with the pipe. It seems nothing is really the size it is named. In the manufacturing world, this is called nominal sizing. This guide was created to explain or clarify the correct sizing and matching of PVC pipe and fittings and the terminology used in this industry.
A Little History About PVC
First discovered way back in , it wasn’t until the early 20th century that PVC (polyvinyl chloride) was further developed into a more usable plasticized polymer. The rigid, often brittle polymer was combined with various additives to make it more flexible and easier to process. Very soon, it achieved widespread commercial use.
Today, PVC has two basic forms, rigid and flexible. Probably the most common use you can think of is PVC pipe, although it is also used in doors and windows, bottles, packaging, flooring and even in those little cards we use everyday instead of paper currency, just to name a few. Polyvinyl chloride (PVC) is the third most widely used plastic polymer in the world, with over half of that being used in making pipe and fittings for pipe that are used in our water and drainage systems.
Some of the specifics that make rigid PVC so popular are availability, cost, density and strength, and its resistance to chemicals and alkalis.
PVC Pipe Class and Schedule Ratings
PVC pipe with a schedule (SCH) rating such as SCH 40 or SCH 80 is most common in plumbing and irrigation use. The larger the SCH number the stronger the pipe. While SCH 40; SCH 80; and SCH 120 are the same outside dimension for compatibility of fittings, the wall is thicker on SCH 80 & SCH 120 pipe. SCH 40 pipe is commonly used in pressure applications such as mainlines (pipes that are under constant pressure, located before the sprinkler zone valves) for sprinkler irrigation systems. SCH 40 pipe has relatively high PSI ratings. SCH 40 PVC pipe should never be threaded, just add an adapter fitting when threads are needed. Thicker walled SCH 80 is very common in threaded pipe nipples as the thicker wall allows for threads to be cut or molded into it.
Class (CL) ratings are based on the water pressure rating of the pipe. Available PVC classes include CL125 for 125 PSI; CL165 for 165 PSI; CL200 for 200 PSI; and CL315 for 315 PSI. Pressure ratings are usually given for water at 73°F.
Maximum Working Pressure for SCH 40 & SCH 80 PVC Pipe
Nominal Pipe Size
Max PSI SCH 40 Pipe
Max PSI SCH 80 Pipe
½”
600
850
¾”
480
690
1”
450
630
1 ¼”
370
520
1 ½”
330
470
2”
280
400
2 ½”
300
420
3”
260
370
4”
220
320
5”
190
N/A
6”
180
280
While the maximum operating temperature may be listed as 140°F, the service temperature rating is between 41° - 122°F continuous, and short or intermittent up to 140°F. The higher the temperature, the lower the pressure rating. See the chart for the de-rating factors at temperatures higher than 73°F.
De-Rating Table
Operating Temperature (°F)
73
80
90
100
110
120
130
140
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De-Rating Factor
1.00
0.88
.075
0.62
0.51
0.40
0.31
0.22
To calculate this, take the working pressure of your PVC pipe SCH/class and size at 73° F and multiply by the de-rating factor nearest the operating temperature to get the maximum working pressure in your application.
1” SCH 40 @ 73°F = 450 PSI so if operating temperature will be 110°F then the equation is:
450 PSI × 0.51 = 229.5 PSI maximum working pressure
Matching Your PVC Pipe and Fittings
PVC pipe sizes are standardized nationally with iron pipe sizes and are identified by the nominal inside diameter (ID) pipe size. A common mistake is measuring the outside diameter of the PVC pipe which gives a much larger and incorrect size. The sizes, such as 1/2", 3/4", 1", etc... are referred to as "nominal" sizes, meaning "in name only" and does not necessarily match any exact measurement of the item. Here is a chart showing the nominal size, the actual outside diameter (OD), the minimum wall thickness and the average inside diameter (ID) for Schedule 40 PVC pipe.
Once you confirm your PVC pipe size then selecting a fitting is easy, just match the nominal pipe size to the corresponding fitting size.
To recap, the most important thing to remember when working with PVC pipe and fittings is how the nominal size is noted. A 1" fitting will fit on a 1" pipe. This is true for both schedule 40 or 80. So, while a 1" socket fitting has an opening wider than 1" across, it will fit on a 1" pipe because the outside diameter of that pipe is also greater than 1".
PVC Fitting Connections
Schedule 40 PVC pipe does not have threaded ends so a slip fitting is needed to join sections of pipe together. Slip fittings will slip right on the PVC pipe and may seem tight, but will not hold water. The connection must be sealed. For a leak-proof seal on a slip fitting, you will need both PVC primer and PVC cement. The primer softens the inside of the fitting, preparing it to bond, while the cement bonds the two pieces together tight.
As an easy alternative to the hassle of primer and cement, HydroRain offers PVC-Lock fittings that are a simple push-fit style that do not require gluing for a leak-proof seal. Another advantage of PVCL is the fittings are removable and reusable. A size specific special release tool is required for removal. Here is a link to our selection of PVC-Lock Fittings.
Another alternative, to creating connections that can be taken apart, is PVC threaded fittings. Keep in mind that threaded fittings are a weak point in any piping system and the working pressure is reduced by 50% when a threaded connection is used. Proper technique is required for a secure leakproof connection. Many manufacturers have differing recommendations for using any chemical aid when joining plastic threaded components. Chemicals, such as teflon and pipe dope can degrade the plastic and increase risk of premature failure. We suggest following manufacturers recommendations. The leak-proof seal of a male and female threaded PVC connection can be made using a thread sealant compatible with the material. The sealant is applied around the male (outside) threads, then the two (male and female fittings) are screwed together, finger tight, then one to two more turns at most. Over tightening can cause stress cracks that will fail!
Here is a list of some of the common terminology used in describing PVC fittings.
Slip refers to a fitting with no threads that slips over the pipe and requires primer and glue (solvent and cement) to create a leak proof seal.
Socket (SOC) is the equivalent of a female end and slips over the PVC pipe of same size.
Spigot (SPG) is the equivalent of a male end and fits into a socket end of the named size. PVC pipe has spigot ends and requires socket fittings to join.
FPT or FIPT refers to a female pipe threaded connection. This means the threads are on the inside of the fitting. Connection is to a male pipe thread fitting.
MPT or MIPT refers to male pipe threaded connection with threads on the outside of the fitting. Connection is to a female pipe threaded connection.
Coupler, Coupling, or Union is a simple straight fitting used to join or “couple” two parts together. Couplers can be slip or female threads or a combination of the two, joining pipe to pipe, pipe to fitting or fitting to fitting. The union coupler has threaded tightening rings or collars on one or both ends for easy installation or removal of the connected parts.
Tee is just what it sounds like, a “T” shaped fitting to connect parts in three different directions with two being a straight line and one creating an angle (usually 90 degree). Tee fittings can have slip or threaded connections.
Elbow is used to make a turn in your line, most often found in 90 and 45 degree angles. Others may be available but much less common. Available in slip or threaded connections.
Cross is also just like it sounds. It is used to join four pipes at four 90 degree angles. Usually found with slip connections.
Adapter is a fitting with different connection types. Used to adapt from one type of part to another. Slip to a threaded connection or pipe thread to hose thread.
Bushing is similar to an adapter, but is mainly used to join pipes of two different sizes together. Usually threaded or spigot.
Cap or End Cap closes the end of your pipe. A cap is a socket or female fitting.
Plug has the same purpose as the cap but it is a spigot or male fitting. Most common with threads for plugging or closing a fitting.
PVC is a thermoplastic material that is lightweight, easy to install, and resistant to corrosion and chemicals. PVC or polyvinyl chloride pipes are widely used in various applications due to their versatility, durability, and cost-effectiveness. These pipes are generally used for plumbing systems, irrigation, drainage, sewerage, and underground cable protection. PVC pipes come in various pressure ratings to suit different applications, whether it is for low-pressure water supply or high-pressure industrial processes.
While deciding to purchase PVC pipes, it is necessary to consider various factors to ensure that we are getting a high-quality product.
1. Material
PVC pipes may vary in terms of material quality. The quality of PVC pipes depends on the type of PVC resin used in their manufacturing. Thus we should look for pipes made from high-quality virgin PVC resin, as this ensures better strength, durability, and resistance to chemicals.
2. Resistance to environmental factors
Pipes need to be able to adapt to a variety of hard-hitting situations. They should be able to tolerate extreme cold and heat conditions. Metal components may become fragile in cold weather. Steel pipes may explode and rupture if left unchecked due to ice blockage. Likewise, hot temperatures may cause pipes to burst for a variety of reasons. Metal can expand when exposed to direct heat. When the pipe can no longer withstand the high heat, it will burst. Therefore, we need to keep these points in mind while buying plumbing pipes to help us to make an informed decision.
3. Manufacturing Process
The manufacturing process has great significance in determining the quality of PVC pipes. As it is a tested fact that pipes manufactured using advanced extrusion techniques, such as computerized control systems, provide better uniformity, strength, and resistance to cracks and leaks.
4. Tolerance to Pressure
PVC pipes are manufactured and available in different pressure ratings, indicating their capacity to tolerate internal pressure. It is better to consider the required pressure rating based on our application.
5. Certifications
When deciding to buy PVC pipes we should always try to buy PVC pipes from a company that complies with relevant industry standards and certifications. For example, in India, the certification for PVC pipes is provided by various organizations and government bodies. The Bureau of Indian Standards (BIS) is the primary organization responsible for setting standards and issuing certifications for various products, including PVC pipes. BIS certification ensures that the products meet the required quality, safety, and performance standards. For PVC pipes in India, the relevant standard is IS:, which specifies the requirements for PVC pipes for potable water supplies.
6. Durability
While purchasing PVC pipes, we should look for pipes that are known for their durability. For it, the reputation of the manufacturer also should be kept in mind. The reputation of the manufacturer is also a mark of durability. High-quality PVC pipes should have a long lifespan and be resistant to aging, weathering, and degradation caused by various chemicals and environmental factors. Reputed manufacturers always assure a warranty for their PVC pipes. We should consider the availability of after-sales support, technical assistance, and a responsive customer service team.
7. Resistant to Impact
Impact resistance is one of the best features of PVC pipes. PVC pipes should be impact-resistant to withstand accidental impacts or heavy loads. It is to be ensured that the pipes have high impact strength, reducing the risk of damage or cracking during installation.
8. Resistance to Chemical
We should check the chemical resistance properties of the pipes to ensure they are compatible with the substances they may come in contact with. PVC pipes are often used to transport various fluids, including water, chemicals, and corrosive substances.
9. Sizes and Dimensions
PVC pipes come in various sizes and dimensions. We should check the diameter, length, and wall thickness of the pipes ensuring they meet our specific requirements. Accuracy in dimensions is important for proper fitting and efficient flow of fluids.
10. Jointing System
To make a continuous pipeline, pipes are joined together. Generally, PVC pipes are joined by using solvent cement, which creates a strong and leak-proof bond. We need to consider the type of jointing system used with the pipes, ensuring it is reliable, easy to install, and provides a secure connection.
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