10 exam-style questions with answers and explanations, straight from our 1,030-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.
The LA-PLB exam has 145 questions and runs 7 hours.
These 10 free LA-PLB questions are organized by exam domain, so you can see how each part of the Louisiana Master Plumber License Exam blueprint is tested. Reveal the answer and explanation under each question.
Following installation of a non-bypass pressure-reducing valve set to 60 psi on a 96-psi service, a gauge shows pressure rising only during water-heater recovery, and the properly rated relief valve begins to drip. What correction addresses the cause?
Correct answer: C - Add a potable expansion tank on the cold-water side
At a lavatory, a 2-inch trap arm measures 7 feet from the trap weir to its dry-vent opening. Before reaching the vent, the arm falls 2.5 inches; the takeoff is above the drain centerline. Identify the controlling defect.
Correct answer: D - The fall before the vent exceeds one pipe diameter
For the hydraulically remote fixture, source pressure is 70 psi, elevation is 32 feet above the service entrance, meter and backflow-device losses total 7 psi, and 15 psi residual pressure is required. Using 0.433 psi per foot of elevation gain, how much pressure loss may be allowed through pipe and fittings, rounded to the nearest tenth?
Correct answer: B - 34.1 psi
Potable water must remain directly connected to a process line carrying concentrated boiler-treatment chemical. The process pump can create backpressure, and a physical air gap cannot be maintained. Select the backflow preventer suited to this hazard.
Correct answer: A - RP/RPZ assembly
During final inspection, a 3/4-inch temperature-and-pressure relief valve is found discharging through full-size piping by gravity to a point 4 inches above an approved receptor. The pipe end has a threaded cap drilled with a 1/4-inch hole to keep insects out. What must be changed before approval?
Correct answer: A - Remove the cap and leave the outlet unobstructed
Clear-looking septic-tank effluent is proposed for discharge to a roadside ditch because the solids have settled and the tank was recently pumped. Which conclusion is technically sound?
Correct answer: B - A septic tank provides primary settling, not disinfection or approval for ditch discharge
A three-bedroom residence has an average 60-minute percolation-test drop of 6 inches. Louisiana's absorption-trench table requires 110 feet per bedroom at that result. No individual trench may exceed 100 feet, and at least two trenches are required. All other site requirements are met. Select the compliant arrangement.
Correct answer: C - Three 100-foot trenches and one 30-foot trench
On a bonded Louisiana public project, a plumbing supplier remains unpaid by a subcontractor. Because public property is not treated like ordinary private property for lien purposes, where should the supplier look for payment security?
Correct answer: A - Payment bond
During a competent person's inspection of a 4.5-foot-deep trench in unstable soil, a fresh tension crack is found near the wall. A compliant access ladder is already in place. What additional cave-in protection is required?
Correct answer: D - Install a protective system before employees enter
In a pricing worksheet, anticipated profit is divided by job cost and the result is labeled gross margin. What is the correct name for that percentage?
Correct answer: C - Rename it markup; gross margin divides profit by revenue
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