National Journeyman Plumber (UPC 2021) Practice Test

In the plumbing codes, what is an air gap in a water supply system?

An air gap is an unobstructed vertical opening through the atmosphere between the supply outlet and the flood level rim. Because the water must jump the gap, nothing can be siphoned back into the supply.

Which job is normally exempt from a plumbing permit under the model codes?

Both codes exempt minor repairs such as stopping leaks and clearing stoppages when no piping is replaced or relocated. New fixtures, water heaters and rerouted piping need a permit.

What is the minimum distance from the center of a water closet to a side wall or partition?

Both codes require at least 15 inches from the centerline of a water closet to any side wall, partition or vanity.

What is the minimum size of a building water service pipe?

Both codes set 3/4 inch as the smallest water service; it must be larger when the demand and length require it.

Under the UPC, what is the standard minimum slope for a 3-inch horizontal drain?

The UPC sets 1/4 inch per foot (2%) as the standard slope and allows a flatter 1/8 inch per foot only for pipe 4 inches and larger where the AHJ approves it; its sizing table assumes 1/4 inch per foot.

What is the main purpose of a plumbing vent system?

Vents let air in and out of the drainage system so the flow of waste does not suck or push the water out of the traps; they also carry sewer gas outdoors.

What safety device must every storage-type water heater have?

A T&P relief valve (or separate temperature and pressure valves) opens before the tank can overheat or overpressure and explode.

Use 1,000 Btu per cubic foot for natural gas. A furnace is rated 80,000 Btu/h. What gas flow does it need?

Divide the input rating by the heating value of the gas. For natural gas at 1,000 Btu/ft³, CFH is Btu/h divided by 1,000.

What is the correct order for making a PVC solvent-cement joint?

Preparation comes first (square cut, deburr and chamfer, clean, dry fit), then primer and cement while the primer is still wet, then a quarter turn and a hold so the pipe does not push back out.

An indirect waste pipe ends below the flood level rim of a floor sink but above its trap seal, and the joint is open to the air. This connection is called:

An air break discharges into a receptor below its flood level rim but above the trap seal without a sealed joint. An air gap would end above the flood level rim.

When must the rough-in inspection of drainage, vent and water piping be made?

Rough-in work must be inspected and tested before it is covered by walls, ceilings or backfill. Work covered too early can be ordered uncovered.

Two water closets are installed side by side. What is the minimum center-to-center spacing?

Water closets must be at least 30 inches center to center, which is the 15-inch side clearance doubled.

Under the UPC, when may a water pipe be laid in the same trench as a building sewer made of a material not approved inside buildings?

The UPC allows a common trench only with the water pipe on a solid shelf cut to one side, its bottom at least 12 inches above the top of the sewer, with 12 inches of horizontal clearance.

A 40-ft horizontal drain is laid at 1/4 inch per foot. How much total fall does it have?

Multiply the slope per foot by the length. Using 1/8 inch per foot by mistake gives 5 inches.

How many vent pipes must extend to the outdoors from a building's drainage system?

Every building drainage system needs at least one vent extending to the outdoors to relieve positive pressure; AAVs cannot replace it.

At what maximum temperature must a water heater's temperature relief function open?

The temperature relief is set at no more than 210°F, below the 212°F boiling point at atmospheric pressure, so the stored water cannot flash to steam.

Use 1,000 Btu per cubic foot. A house has a 100,000 Btu/h furnace, a 40,000 Btu/h water heater, a 65,000 Btu/h range and a 35,000 Btu/h dryer. What total gas load must the piping carry?

Add every appliance's input, then convert to CFH. Leaving out the dryer gives 205 CFH.

Why is a slight bevel (chamfer) put on the outside edge of a PVC pipe end before cementing?

A square sharp edge wipes the cement out of the socket as the pipe goes in; a small chamfer keeps the cement in the joint.

What is backflow?

Backflow means contaminated or unwanted water entering the potable supply from anywhere other than its intended source. It happens by backpressure or backsiphonage.

Who furnishes the equipment, material and labor for the required plumbing tests?

The codes put the cost and work of testing on the permit holder or installer. The inspector witnesses the test.