Caps

What Is a Cap Used For in Plumbing?

A plumbing cap comes in many different materials (black malleable, galvanized, copper, pvc, cpvc, and more...) is a fitting used to close off the end of a pipe or fitting. Its main function is to:

• Seal a pipe end
• Stop water, gas, or air flow
• Terminate or temporarily block a line

What Caps Are Commonly Used For

• Permanently closing an unused pipe
• Temporarily sealing a line during renovations
• Capping future branch connections
• pressure testing a plumbing system
• Isolating abandoned fixtures or appliances

How Caps Work

Caps install over or onto the end of a pipe:

• Threaded Cap – Screws onto male pipe threads
• Slip / Socket Cap (PVC or Copper) – Glued or soldered over pipe
• Press Cap – Pressed onto copper pipe with a press tool
• Push-to-Connect Cap – Pushes onto pipe (temporary or permanent)
• Once installed, the cap creates a watertight or airtight seal.

Common Materials

• PVC / CPVC
• Copper
• Brass
• Galvanized
• Black malleable iron
• Stainless steel

Simple Example

You remove an old sink but plan to add one later. You install a ½" threaded cap on the water line so the rest of the system can stay pressurized.

In Plain English

A plumbing cap is used to close off the end of a pipe so nothing can flow through it.