How to Assemble PVC - Plumbing Basics, Part 4
Tools Needed For Assembling PVC
- A tape measure. There is no way to accurately “eyeball” a PVC pipe measurement and make the proper cuts.
- A marker to mark your pipes.
- A hacksaw or Pipe cutter.
- PVC primer and cement/glue.
How to Properly Measure PVC Pipe
When measuring the length of PVC pipe for attachment to a fitting or valve you must include the depth of the fitting. The pipe must completely enter the fitting and seat correctly into the socket. Look inside a slip PVC fitting and you’ll see an inside lip that prevents the pipe from going in farther. Use a tape measure to determine how much pipe is needed to slide completely into the fitting until it is stopped by the lip.
Do not attempt to push the pipe into the fitting to get the measurement. Many PVC fittings are slightly tapered and won’t allow you, in most cases, to fully seat “dry” pipe. We’ll explain this in detail when we get into how to glue PVC. The take-away is to use the tape measure to calculate the depth of the fitting.
1. Cut The PVC
The most common way to cut PVC pipe is with a hack saw because most folks have one in the garage. A hack saw blade is designed for cutting metal but works just fine for PVC as long as you clean up the cut thereafter. There are a variety of "PVC Pipe Cutters" available as well so just choose the solution that suits you. PVC cutters are easy to use and make clean cuts, great for when you have multiple cuts to make. You can find one for less than $20 in most hardware stores.
How To Cut PVC
- Mark the pipe where you want to cut. Make sure the line is squared up. The cut should be square, not on an angle because a square cut makes the best seal inside fittings.
- Hold the pipe securely against a flat surface so it does not move around while you use the saw. A vice will work to hold it in place if you have access to one, just don't overtighten it and crack the PVC.
- Make slow, smooth strokes with the saw. This will prevent chipping on the end of the pipe. As the pros say “Let the saw do the work.”
2. Remove the Burrs!
When you cut PVC with a hacksaw it leaves a rough edge with burrs. The burrs are small pieces of PVC that are loosely attached to the end of the pipe. The burrs will make it impossible to slide the pipe into a valve or fitting. Burrs left inside the pipe will eventually pass into the aquarium.
How To Remove Burrs
- Using a sharp blade, like a box cutter, run the blade around the outer and inner edge of the pipe. Hold the blade at an angle for a smooth pass.
- Use fine-grade (120 grit) sandpaper to gently brush away burrs on the inner and outer rim of the pipe. Don’t aggressively sand the pipe, just enough to remove the burrs.
3. Test Fit Carefully
"Dry fitting" is when you assemble the PVC system without glue to check your measurements. The problem is many PVC fittings are designed to connect to pipes by friction fit. This means the fitting is slightly tapered to make an extremely snug fit, so there are no gaps for PVC cement to fill in. You may have a really hard time removing PVC from fittings after dry fitting and they can get stuck together. Be careful and don't press the pipes fully into place. Its ok, to simply gauge your cuts by eye.
4. Cement Your PVC & Fittings
PVC cement is not really like cement or glue, it is a special solvent designed to slightly dissolve the surface of the PVC pipe and fitting. Once the PVC components are assembled, the solvent evaporates, and the PVC re-hardens. The two components are now one and are “welded” together with a water-tight seal. To get a water-tight seal the pipe end must be square, free of burrs, and free of dirt and oils, the same goes for the fittings.
There are several kinds of PVC cement (and primers) available, each formulated for specific types of plastic. Make sure the product is specifically for PVC material. CPVC pipe cement is made for CPVC (chlorinated polyvinyl chloride) pipe, and should not be used with PVC.
Why Use PVC Primer?
PVC primer starts a chemical reaction that softens the PVC and washes away residue from the plastic surface. Primer reduces the chances of poor bonding between the PVC parts. Primer is typically dyed purple. This makes it easy for plumbing inspectors to see if primer was used on a home’s plumbing system. Some aquarists don’t like the look of purple stains on their filtration system. PVC can be cemented without primer but you must be sure there is no grease or oils on the components when you glue them together.
How To Cement PVC
The following steps include using primer when assembling your PVC system. Have all your components ready before starting the assembly process. You’ll want to work relatively fast when working with primer and cement. Primer and PVC cement can get messy when you assemble plumbing. Prepare for drips by placing cardboard under your work. Gloves will protect your hands from the solvent and purple primer stains.
- Using the dauber on the can’s lid, apply primer to the inside of the fitting and outside of the PVC pipe. Primer is only active while it is wet, which is about 10 seconds.
- Immediately apply PVC cement to the same areas that are primed. Typically, that’s both the end of the pipe and inside the fitting.
- Twist the pipe a quarter-turn as you push it into the fitting. This will cause the cement to spread and fill any gaps. The softened PVC will allow you to completely push the pipe into the tapered fitting.
- Check for alignment. You have a very short amount of time to make slight corrections.
- Hold the pipe and fitting together firmly for about 30 seconds which ensures a secure weld.
- Wipe away excess cement, for a cleaner look.
- Allow the cement to cure for 24 hours before pumping water through the system.
Working With Threaded PVC Fittings
Threaded PVC and fittings use tapered threads. All tapered pipe threads have a small spiral leak path between the mating threads. The leak path needs to be sealed during the assembly process to obtain a leak-free connection. The most common solution is the use of Teflon tape. Teflon tape is wrapped around the male threads before screwing into the fitting. The idea is to plug the leak path with a layer of tape.
While Teflon has been used with success, pros don’t recommend it. Here’s why. The slippery Teflon makes it easy to over-tighten the fitting. This can cause the female fitting to develop stress cracks and leaks. The Teflon tape also “bunches up” in the threads, putting more pressure on the female fitting. If the male fitting is backed out a little, the Teflon seal is often lost, allowing for drips.
Plumbing pros recommend a non-hardening sealing paste. After applying the paste, hand-tighten the fitting until snug, then tighten one to two more turns at most. This is all that’s required for a stress-free connection that won’t leak. Avoid using a wrench if possible.
Read The Plumbing Basics Series:
- PVC – Plumbing Basics, Part 1 – What you Should Know
- How to Size Bulkhead Fittings – Plumbing Basics, Part 2
- How to Choose the Right Valve – Plumbing Basics, Part 3
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