General Plumbing Knowledge
This domain tests the vocabulary, materials, and basic physics that the other four domains assume: which pipe materials may carry potable water, how joints are made, how pipe is supported, and how pressure, elevation, and fixture units relate. Questions usually ask you to choose a material or predict a pressure, not just define a term.
Materials and joining
Copper water tube comes in types K, L, and M, in decreasing wall thickness; K is heaviest and is used underground and for services, L is the common interior choice, and M is thinner and restricted in many applications. Join copper with lead-free soldered fittings, press fittings, or brazed joints where required. ABS and PVC are drainage-only materials joined by solvent cement matched to the plastic - never use ABS cement on PVC. Cast iron soil pipe uses no-hub couplings with stainless steel bands. PEX and CPVC are common potable choices; PEX uses insert or crimp fittings and must be protected from UV and abrasion.
Pressure, head, and fixture units
Static pressure changes 1 psi per 2.31 feet of elevation, so 10 feet of rise costs about 4.3 psi. Fixture units let you add unlike fixtures into one load: a tank water closet is 3 drainage fixture units, a lavatory 1, a bathtub or shower 2.
Worked example
A meter outlet reads 62 psi. A hose bibb sits 18 ft above the meter. Static pressure at the bibb is 62 − (18 ÷ 2.31) = 62 − 7.8 ≈ 54 psi. If the bibb were 18 ft below the meter it would read about 70 psi. Reasoning: elevation alone changes static pressure; friction matters only when water flows.
Traps
Common errors: using PVC for hot potable distribution, applying ABS cement to PVC, omitting dielectric unions where copper meets steel, and multiplying by 2.31 when you should divide. Watch too for support spacing and protection from freezing and physical damage.