Maya Ellison
Plastic pipes are a standard for plumbing due to their safety, sturdiness, and low cost. They are also easy to install, adjust, and tighten, and they don't corrode. When repairing a section of pipe, it is recommended to use a mission coupling that clamps over the last joint, providing a better seal and peace of mind. This is because it can be challenging to flex rigid pipes with large diameters enough to slide on the last fitting and fully seat it. While plastic pipes are durable, they can degrade over time, and even small leaks can lead to significant water damage. Therefore, it is important to choose the right tools and take the necessary precautions when working with plastic pipes.
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What You'll Learn
Use a mission coupling that clamps over the last joint
When repairing a section of pipe in an existing run, it is not advisable to cement or solvent-weld all the new couplings. This is because most drain systems use rigid pipes with a large diameter, which cannot be flexed enough to slide on the last fitting and get it to seat fully. Instead, it is recommended to use a "mission" coupling that clamps over the last joint. This provides flexibility and a better seal overall, preventing leaks and water damage.
Mission couplings consist of a metal sleeve with band clamps that can be tightened to seal pipe joints. They are available in various sizes, ranging from 1" to 4", and are suitable for sewage, drain, and soil applications. They can be used with cast iron, plastic (PVC/ABS/CPVC), steel, copper, and tubular pipes. It is important to note that mission couplings are more expensive than plastic couplings, and it is recommended to buy couplings with full steel sleeves. Additionally, ensure that the mission couplings meet the code requirements in your area.
To install a mission coupling, slide it onto one pipe and cement plastic couplings onto the other two pipes. Center the mission coupling over the third joint and tighten the bands firmly. This will secure the joint and prevent any leaks. In some cases, professionals might even use two mission couplings for added security.
It is worth mentioning that mission couplings are not suitable for underground burial, and some manufacturers recommend using heavyweight or heavy-duty couplings for such applications. Additionally, mission couplings are not interchangeable with potable water applications as they do not meet the low-lead criteria defined in the Safe Drinking Water Act.
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Don't cement all new couplings
When repairing a section of pipe in an existing run, it is advisable not to cement all the new couplings. Most drain systems use rigid pipes with large diameters. Cementing all the new couplings may cause issues as the pipes cannot be flexed enough to slide on the last fitting and get it to seat fully. This may result in leaks. Instead, a "mission" coupling can be used to clamp over the last joint, providing a better seal and peace of mind. Mission couplings are more expensive than plastic couplings but are worth the investment. In tight situations, two mission couplings can be used.
When working with PVC pipes, it is important to ensure proper ventilation or wear an approved organic vapor respirator to avoid the health risks associated with solvent vapors from PVC primer and cement. To avoid leaks, it is crucial to dry-fit the pipes before gluing to ensure a proper fit. Square pipe ends are recommended as they fit snugly into the fittings, creating a smooth interior surface for better water flow. Before gluing, it is important to prime the pipe ends and the mating sockets of the fitting. After applying cement, push the pipes into the fittings and give them a quarter-turn twist.
In situations where there is no "give" or flexibility in the pipes, solvent-weld slip couplings can be used. Rubber couplings are a popular code-approved option, but they may not provide the desired stiffness and durability of a permanent connection. Before cutting into the existing pipe, it is crucial to ensure that no water is present, as even a small amount can spoil a joint that's being glued.
For connecting PVC pipes, it is recommended to use a little extra glue and feed it over one pipe and then the other. Compression fittings are also an option, especially if it is just a drain and not a pressure pipe.
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Metal vs. plastic drain pipes
Metal pipes have been the traditional go-to option for plumbing systems. Metal pipes are made from copper, brass, cast iron, or steel. Metal pipes are incredibly durable and long-lasting, but they are susceptible to corrosion and rusting, which can cause flaking and result in rusty tap water. Metal pipes are also more expensive than plastic pipes and are heavier and more challenging to work with. However, they are more rigid and fire-resistant than plastic pipes, and they are easier to branch off and replace.
Plastic pipes (PVC/CPVC/ABS) are a modern, standard alternative for plumbing and DIY projects. They are safe, sturdy, and cost-effective. Plastic pipes are also easier to work with as they are lightweight and can be easily cut and fitted into tight spaces. Plastic pipes are also simple to connect, as there are multiple installation techniques that don't require welding, saving time and effort. Additionally, due to their popularity, it is usually easier to find uncommon components for plastic pipes.
One disadvantage of plastic pipes is that they are not as durable as metal pipes, especially when it comes to heat resistance. Plastic pipes may become brittle over time and need to be replaced more frequently. They are also not suitable for plumbing systems that transport potable water or water under high pressure, unless specific types of plastic, such as polybutylene or chlorinated polyvinyl chloride (CPVC), are used.
When deciding between metal and plastic drain pipes, it is important to consider factors such as durability, cost, ease of installation, and suitability for the specific plumbing application. Both options have their own advantages and disadvantages, and the best choice depends on the specific requirements of the project.
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Avoid overtightening supply lines
Overtightening supply lines is a common mistake made by DIYers. It is tempting to crank supply lines on tight, but this can wreck rubber seals and crack threaded nuts. It can also cause the hex nuts and bolts to break, leading to burst faucets and toilet water supply lines.
To avoid overtightening, make the connections at both ends of the supply line finger-tight, then give them another one-eighth to one-quarter turn with pliers. If they leak, tighten them a little more. It is important to remember that plumbing pipe fittings don't need to be super tight to function properly. In fact, pipes should only be hand-tight to help aid the flow of water. If you tighten the fittings too much, you may strip the threads inside the fitting or on the outside of the pipe.
If you are working with plastic pipes, be sure to use the right tools. Trying to remove an old pipe with an ordinary wrench or slip joint pliers can break the pipe. It is also important to use the correct tape. Use thin white or thick pink thread tape for fittings that carry water, and yellow gas-rated tape for threaded gas line connections. Never use thread tape on compression or flare fittings.
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Thread sealants
There are several types of thread sealants available, each with its own advantages and disadvantages. One commonly used type is pipe dope, a solvent-based product that hardens once the solvent evaporates. Pipe dope is relatively inexpensive and easy to use, and it can be used with any pipe material, including plastic. It provides a moderate to strong seal and is suitable for connections that may be subject to vibration or temperature changes. However, pipe dope tends to shrink over time, which can cause the threads to crack or pull away from the dope, leading to leaks. Pipe dope can be applied with a brush or spatula, or sometimes by hand.
Another type of thread sealant is polytetrafluoroethylene (PTFE), a fluoropolymer or plastic that contains fluorine atoms. PTFE is chemically unreactive, slippery, and stable at extreme temperatures, making it ideal for use in plumbing. It has a high melting point, is hydrophobic, and is chemically inert, meaning it won't dissolve or break down in common organic solvents. PTFE sealants can take the form of tapes or pastes, and they can be easily assembled and disassembled. However, it is important not to overtighten PTFE sealants, as the lubrication they provide can make it easier to crack the fitting.
Other types of thread sealants include anaerobic sealants, which cure in the absence of air and are ideal for metal-to-metal connections, and wicking, a traditional method that uses a string-like material to fill the gaps between threads. Wicking is often used in combination with pipe dope for added protection against leaks. For plastic pipes, Teflon tape is a great choice as it is a no-mess solution that lubricates the threads for easier disassembly.
When choosing a thread sealant, it is important to consider the specific application and the type of pipe being used. Not all plumbing connections require the same sealing method, and it is crucial to ensure that the selected sealant is compatible with the pipe material and connection type.
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Frequently asked questions
A mission coupling is a metal sleeve with band clamps that can be tightened to seal pipe joints.
Mission couplings are more flexible than cement or plastic couplings, which can be difficult to slide on and fully seat.
First, buy matching replacement parts and cut the plastic at a right angle. Then, slide the mission coupling onto one pipe and cement plastic couplings onto the other two pipes. Finally, centre the mission coupling over the third joint and tighten the bands firmly.
You can buy mission couplings from plumbing suppliers. Make sure to buy couplings with full steel sleeves and ensure they meet the code requirements in your area.
