Plumbing Basics

83 flashcards by MentisLibrary

Supply and drainage, traps and venting, pipe materials and joining methods, and the repairs that come up on almost every service call. Written the way an apprenticeship textbook explains a system.

What is the main shutoff valve and where is it usually found?
The single valve that isolates all water in the building, normally just inside where the service line enters, ahead of or right after the meter
What is the difference between static pressure and working pressure?
Static pressure is measured with no water flowing; working (residual) pressure is measured while fixtures are running
What is a normal residential water pressure range?
About 40 to 80 psi; codes commonly cap static pressure at fixtures at 80 psi
What does a pressure reducing valve (PRV) do?
Drops incoming high street pressure to a stable, lower house pressure, usually set around 50 to 60 psi
Why does a closed plumbing system need a thermal expansion tank?
Heated water expands, and with a check valve, backflow preventer, or PRV blocking return flow to the main, that expansion raises system pressure with nowhere to go
What is water hammer and what causes it?
A bang or shudder in the piping when fast moving water is stopped abruptly and its momentum slams against a closed valve
What is a water hammer arrestor and how does it differ from an air chamber?
An arrestor is a sealed device with a piston or bladder over a cushion of gas; an air chamber is just a capped stub of pipe holding trapped air
What is trunk and branch water distribution?
A large main line (the trunk) runs through the house and smaller branch lines tee off it to serve fixtures
What is a manifold or home run water distribution system?
A central manifold feeds a dedicated line to each fixture with no tees or fittings in between
What does a hose bibb vacuum breaker protect against?
Back-siphonage of contaminated water, for example from a hose lying in a pool, fertilizer sprayer, or bucket, into the potable supply
What do the letters DWV stand for?
Drain, Waste, and Vent, the piping system that carries used water and waste out and admits air so it flows
What slope is required for horizontal drain piping 2 1/2 inches and smaller?
1/4 inch of fall per foot of run
What is a drainage fixture unit (DFU)?
A relative load value assigned to a fixture that represents its probable discharge, used to size drains, branches, and stacks
What is the difference between the building drain and the building sewer?
The building drain is the lowest horizontal piping inside that collects everything and carries it out; the building sewer starts outside and runs to the public sewer or septic tank
What is a stack vent versus a vent stack?
A stack vent is the extension of a soil or waste stack above the highest fixture branch connected to it; a vent stack is a separate vertical vent pipe that serves the drainage stack
What is a cleanout and where are they required?
An accessible capped opening in the drainage system that lets a cable or jetter reach a blockage
Why should a sanitary tee never be used to turn flow from horizontal to horizontal?
Its short turn geometry lets waste from the branch collide with and dam flow in the main, causing blockages and holding solids
What is the purpose of a P-trap?
It holds a plug of water that blocks sewer gas from entering the room while still letting waste pass through
What is the required trap seal depth?
Standard practice is a minimum of 2 inches and a maximum of 4 inches of water in the trap
What is trap siphonage?
Waste flowing past or through the trap pulls the seal water out with it, leaving the trap dry and open to sewer gas
Why is an S-trap prohibited?
The outlet drops vertically straight out of the trap, so a full fixture discharge siphons the seal right out and leaves the trap dry
What is a trap arm and why is its length limited?
The trap arm is the drain from the trap weir to the vent connection; if it runs too long the pipe fills with water and siphons the trap
Why must the fall on a trap arm not exceed one pipe diameter?
If the trap arm drops more than its own diameter between the trap weir and the vent, the vent opening ends up below the weir and the trap can siphon
What is an individual vent?
A vent that serves one fixture trap and connects to the vent system or terminates outside on its own
What is a common vent?
One vent serving two fixture traps that connect to the drainage system at the same level
What is wet venting?
A drain pipe that carries the discharge of one fixture while also serving as the vent for another
What is an air admittance valve (AAV) and what are its limits?
A one way valve that opens under negative pressure to admit air into the drain, then seals shut so sewer gas cannot escape
Where may a vent terminate above a roof?
Above the roof surface by the amount the code specifies, and set back or raised where it would be near an openable window, door, or air intake
Why are vent pipes sometimes increased in size before passing through the roof in cold climates?
Moist air condenses and freezes at the opening; a larger diameter keeps frost from closing the vent off
How do copper tube types K, L, and M differ?
They differ only in wall thickness for the same outside diameter: K is thickest, L is medium, M is thinnest