Pipe Joining and Fitting Methods Flashcards

When joining PEX-A tubing using the expansion method, what must be done immediately after the pipe end is expanded?

Answer: Assemble the fitting immediately — PEX-A has shape memory and will contract to grip the fitting barb as it warms

PEX-A has thermal memory and will shrink back to its original diameter after expansion, permanently gripping the fitting barb to create a leak-free mechanical seal.

Which type of fitting incorporates a sight (witness) hole that confirms the pipe has been fully inserted to the correct depth?

Answer: Push-fit (press-to-connect) fittings — the sight hole confirms full pipe insertion before the O-ring seals

Push-fit fittings incorporate a transparent or side-positioned sight window so the installer can visually confirm the pipe has reached the full insertion depth required for the O-ring to form a proper seal.

What precautions should be taken when soldering a joint adjacent to an installed ball valve or gate valve?

Answer: Open the valve fully and use a wet rag as a heat sink between the torch flame and the valve body

An open valve reduces heat buildup at the seat area, and a wet rag heat sink absorbs excess heat before it reaches the valve's rubber or EPDM seals, which would be destroyed by soldering temperatures.

What is the primary functional difference between a coupling and a union in a threaded steel piping system?

Answer: A union allows a section of pipe to be disconnected without rotating the pipe; a coupling requires the pipe to be turned during disassembly

A union consists of three parts allowing the joint to be broken and remade without rotating the connected pipes, making it essential at serviceable locations such as near water heaters, pumps, or valves.

What does an electrofusion control unit supply when joining polyethylene (PE) gas pipe with electrofusion fittings?

Answer: A precise electrical current for a specified time to activate the resistance wire and fuse the pipe to the fitting

Electrofusion control units deliver a precisely regulated current for the manufacturer-specified time, melting the embedded resistance wire and surrounding polyethylene to permanently fuse the fitting to the pipe.

How many threads should remain visible outside a fitting after a properly wrench-tightened NPT threaded steel pipe joint?

Answer: Approximately 3 to 5 threads should remain visible outside the fitting

Seeing 3–5 threads outside the fitting after wrench-tightening confirms that the tapered NPT threads have fully engaged inside the fitting to create a wedging seal without bottoming out.

Which joining method is NOT rated for pressurized copper water supply piping and therefore cannot be used on supply lines?

Answer: No-hub (Mission-type) banded rubber couplings — rated for drain, waste, and vent piping only, not pressure piping

No-hub couplings are designed for low-pressure gravity drain piping and are not rated for the working pressures found in domestic water supply systems.