One of the most common concerns about PVC fittings is how tight they should be. Is there really is such a thing as “too tight” when it comes to turning PVC fittings together?
It's important to tighten fittings correctly, and there often is a “just right” when it comes to tightening them. If your fittings aren’t tightened enough, they have the potential to leak. On the other hand, if fittings are tightened too much, there's the potential for breakage of the fitting itself, which can cause leakages. Learning how to correctly tighten a PVC fitting helps ensure a tight seal with no damage of the fitting itself, which in turn leads to an extended life for your fitting.
How to Tighten a PVC Fitting
Threaded PVC fittings sometimes get a bad rap because they're considered weaker than other types of connections. However, many mistakes in installing threaded PVC fittings are due to user error. Luckily, there are a number of different tricks that can help ensure your threaded PVC fittings are tightened correctly.
Male End vs. Female End Threaded Fittings
First things first, it is important to understand how different threaded PVC fittings work. PVC fittings consist of two parts: a male end and a female end. The male end of the PVC fitting is threaded on the outside, and the threads are tapered. This means that the threads increase in size as they go down the fitting. The female end is meant to be the opposite of the male end, meaning the threads on the female end of the PVC fittings are located on the inside, and are tapered to become smaller as they go.
The fact that the threads on PVC fittings are tapered is actually a significant part of the design of the fitting. The tapered design is what's responsible for the tight seal PVC fittings can achieve. Additional turns of the fitting cause the female threads to stretch, however. This stretching puts strain on the threads, and if tightened too much, there's a chance the threading can split or break. This is why it is important to remember not to over-tighten PVC fittings.
Connecting Your PVC Fittings
Now, when it comes to PVC fittings, the work begins before the two ends actually meet. First, it is important to wipe down your threads to ensure they are free of debris, and then apply a PVC thread sealant. The sealant you choose should be specially formulated for use with PVC and other plastics. If the wrong sealant is placed on the threads, there is a chance the PVC will become damaged and the seal will not hold. Once the sealant is applied to your threads, insert the male end into the female fitting.
Once the pieces are together, tighten the connection by hand slowly until the fitting will not turn any more. At this point, you can use a wrench to complete one or two more turns. Do not tighten your fitting past this point. If fittings continue to be tightened after one to two wrench turns, there is a chance the threads within the fitting will not connect correctly, allowing the possibility of a leak within the fitting.
Should You Use Tape, Paste, or Other Lubricants?
On their own, without any type of adhesives or lubricants, PVC fittings will fit fairly snugly. That being said, the connection between the pipe and the fitting will not be watertight. Therefore, if any fluids will be passing through the pipe and fitting, it is important to use some type of adhesive to ensure the seal of your fitting is watertight and will not leak.
PVC Primer and Cement
For slip connections to have a watertight bond, use PVC cement. PVC cements are some of the strongest adhesives approved for use with PVC. PVC cement works in a different way from other adhesives; the cement itself breaks down part of the PVC and bonds the separate pieces on a chemical level. This makes the PVC parts inseparable. PVC cements typically work in minutes. After a primer is applied and is still wet, apply the PVC cement liberally before bonding the two parts.
Interested in PVC primer and cement for your project? Try our handy pack here.
Thread Seal Tape
Thread seal tape can be used if the fitting needs to be unscrewed. Made of PTFE, thread seal tape is wrapped around the male threads of the fitting before the parts are screwed together. Tape can be replaced as needed when the fittings are unscrewed. This is the most common option when it comes to temporarily bonding fittings together. View our tape on our online store.
Pipe Dope
Another option for temporary airtight/watertight bonds is pipe dope (find ours here). A paste that never dries, but occupies minute spaces between threads, this substance should never be used with irrigation systems. The reason for this is that the pipe dope inevitably works its way into the pipe, and then is carried by the liquid to the various irrigation systems being used. From there, the pipe dope clogs the various valves, sprinklers, and drip emitters being used, which will ruin them. So be very careful when using pipe dope, and never use it on irrigation systems.
Caution: Use the Same Schedule Pipe and Fittings
When it comes to preventing splitting and leaking, many people think that they can use threads of different schedules to prevent leaks. This is simply not true. Pipe size and fitting schedule should be the same among parts no matter what. The two most common fitting schedules are schedule 40 (here) and schedule 80 (here). Even if the two are the same pipe size, it is important to never use schedule 40 fittings with schedule 80, as the threads themselves are different sizes. If you bond the two schedules together, the threads won't match up correctly, which can lead to damaging the fittings. Always use the same schedule parts when working with PVC fittings.