Water supply, distribution & backflow: Maryland Journey Plumber Practice Questions

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 IPC, a water service and a building sewer (of a material not approved for use inside buildings) share a trench. What separation is required?

The IPC separates them by 5 ft of earth; the separation is not needed where the bottom of the water pipe is at least 12 inches above the top of the sewer within that 5 ft.

When is a pressure-reducing valve required on a building water supply?

Both codes require a pressure-reducing valve where the static water pressure exceeds 80 psi, so fixtures and appliances are not damaged.

The static pressure at a house is 95 psi. Once a pressure-reducing valve is installed, what else must the plumber check?

Many pressure-reducing valves block backflow toward the street, making a closed system. Thermal expansion from the water heater then needs an expansion tank or other control.

Where is thermal expansion control (such as an expansion tank) required?

When heated water cannot push back into the street main, pressure climbs with every heating cycle. Both codes require an expansion tank or another approved control.

Water hammer arresters are required where:

Quick-closing valves, such as those in clothes washers, dishwashers and solenoid valves, need water hammer arresters (ASSE 1010 or PDI WH-201) placed as close as practical to the valve.

Use 0.433 psi per foot of elevation. The static pressure at the street meter is 65 psi. What is the static pressure at a fixture 35 ft above the meter?

Lifting water costs 0.433 psi per foot. Adding the loss instead of subtracting it gives 80.16 psi.

Use 0.433 psi per foot. A gravity water tank's water level is 92 ft above a ground-floor fixture. What static pressure does the fixture see?

Multiply the height of the water above the outlet by 0.433. Dividing by 0.433 instead gives the wrong 212.47.

Use these values: street static pressure 60 psi; elevation of the highest fixture 20 ft (0.433 psi/ft); meter and backflow device losses 12 psi; minimum pressure needed at the fixture 15 psi; developed length 150 ft. What friction loss per 100 ft can the piping use?

Subtract elevation, device losses and the required residual from the static pressure, then spread what is left over the developed length. Not dividing by the length gives 24.34.

Under the IPC, a water service crosses over a building sewer of a material not approved for use inside buildings, less than 12 inches above it. What is required?

Where the water service crosses a sewer and cannot keep 12 inches of vertical separation, it is sleeved for 5 ft on both sides of the sewer centerline.

Which backflow method gives the highest level of protection?

A properly sized air gap physically separates the outlet from the contaminant, so neither backpressure nor backsiphonage can cause backflow.

Which device protects against both backpressure and backsiphonage for a high hazard (health hazard) connection?

The RPZ has two checks and a relief valve that dumps water if the checks leak; it is rated for high hazard under backpressure and backsiphonage.

A double check valve assembly is acceptable for which kind of connection?

A double check has no relief port, so a failed check is not visible; it is limited to low hazard (pollution) connections.

An atmospheric vacuum breaker (AVB) protects against:

An AVB opens to the air when the supply goes negative. It cannot hold back pressure from downstream, so it is for backsiphonage only.

An atmospheric vacuum breaker must be installed how high, and with what restriction?

An AVB goes at least 6 inches above all downstream piping and outlets, and must not have a valve downstream that would keep it under constant pressure.