Discussion led by Richard, addressing a question from Steven in Cupertino, California about using thread sealants in plumbing connections.
Types of Threads
Straight Threads:
Commonly found in machine threads like nuts and bolts.
These do not get tighter as you turn them unless they hit something.
Tapered Threads:
Used in plumbing.
The thread is smaller at the start and gets larger as it goes up, allowing it to tighten as it is screwed in.
Need for Thread Sealing
Even with tapered threads, a sealant is necessary to make the connection liquid tight.
Types of Thread Sealants
Teflon Tape:
Popular in modern plumbing, especially with plastic.
Comes on rolls, requires pulling it tight to seal onto itself.
Applied by wrapping it around the threads two or three times.
Pipe Dope (Pipe Sealant):
Comes in various brands.
Fills between the threads but remains removable.
Ideal when connections may need to be disassembled later.
Wicking:
Used with pipe dope for older connections, e.g., radiator connections.
A single strand is laid into the threads.
Expands slightly when in contact with liquid, acting like a caulking material.
When Not to Use Thread Sealant
Union Connections:
Example: Radiator valve connections.
Straight threads pull parts together via ground joint.
Might use a small amount of pipe dope on the joint face, not on threads themselves.
Rubber Gasket Connections:
Found in some modern faucets.
Example: Water supply lines to lavatories.
No need for sealant on the threads as the rubber gasket provides the liquid-tight seal when compressed.
Conclusion
Summary: Different situations in plumbing require different sealing techniques, and understanding the type of thread and connection can guide the choice of sealing method.