6.4 Sumps, Sewage Pumps, Ejectors & Backwater Valves

When pumping is required (IPC 712.1)

Building subdrains that cannot discharge to the sewer by gravity must discharge into a tightly covered and vented sump. Automatic pumping equipment, or another approved method, lifts the liquid into the gravity drainage system. In other than existing structures, the sump shall not receive drainage from any piping that can discharge by gravity to the building sewer. Upper floors drain by gravity, and only the low fixtures go to the sump. This also means that a pump failure floods only the low level.

Valves in the discharge (IPC 712.2)

• A check valve and a full-open valve on the discharge side of the check valve are required between the pump or ejector and the gravity drainage system. The order is: pump, then check valve, then full-open valve, then gravity drain.
• Both valves need access. They must be above the sump cover, or, where the discharge pipe is below grade, in an access pit with a removable cover outside the sump.

With the full-open valve downstream of the check valve, a technician can close the full-open valve and service the check valve or pump without draining the discharge line back into the sump.

Sump design (IPC 712.3)

• 712.3.1: pump capacity and head must suit the expected use.
• 712.3.2 sump pit: at least 18 inches in diameter and 24 inches deep unless otherwise approved. It needs access, must receive all drainage by gravity, and is made of tile, concrete, steel, plastic or other approved material with a solid bottom that supports the pump. The pit must have a gastight removable cover installed not more than 2 inches below grade or floor level, strong enough for the loads in the area, and it must be vented under Chapter 9.
• 712.3.3.1 discharge materials: copper or copper alloy, CPVC, ductile iron, PE or PVC. Under 712.3.3.2, pipe and fittings must be rated for the maximum operating pressure and temperature, and be suitable for burial where buried.
• 712.3.4: the effluent level control must keep the effluent from rising to within 2 inches of the invert of the gravity inlet to the sump.
• 712.3.5: the pump discharge connects to a building sewer, building drain, soil or waste stack, or horizontal branch drain. A connection to horizontal piping must be made through a wye fitting into the top of the pipe, at least 10 pipe diameters from the base of any soil stack, waste stack or fixture drain.

Sewage pumps and ejectors (IPC 712.4)

• They must discharge the sump contents to the drainage system automatically.
• 712.4.1: macerating toilet systems meet ASME A112.3.4/CSA B45.9 and are installed per the manufacturer.
• 712.4.2 capacity and solids: pumps or ejectors that receive water closet discharge must handle spherical solids up to and including 2 inches. Other pumps or ejectors must handle solids up to and including 1/2 inch.

Exceptions: grinder pumps that receive water closet discharge need a discharge opening of at least 1-1/4 inches. Macerating toilet assemblies serving a single water closet need a discharge opening of at least 3/4 inch.

Table 712.4.2 relates each discharge size to a minimum flow, which keeps the velocity in the discharge high enough to carry solids. In a 2-inch line, 21 gpm is about 2 feet per second.

Venting sumps (IPC 906.5 and 918.8)

• 906.5.1: drainage piping below sewer level is vented the same way as a gravity system. Vents for sumps with sewage pumps or ejectors, other than pneumatic types, are sized by Table 906.5.1, based on the pump's discharge capacity and the vent's developed length.

Developed length includes an allowance for fittings. If no better value is available, add 50% to the developed length.

• 906.5.2: a pneumatic ejector's air pressure relief pipe connects to an independent vent stack through the roof, and is at least 1-1/4 inches.
• 918.8: air admittance valves shall not be used to vent sumps or tanks, except where the sump or tank vent system has been designed by an engineer. An AAV only admits air and cannot relieve the air pushed out as the sump fills.

Clear-water sumps (IPC 1111 to 1113)

Subsoil drains discharge to a trapped area drain, sump, dry well or approved location above ground. A subsoil sump does not need a gastight cover or a vent (1111.1). Storm and subsoil sump pits are also at least 18 inches in diameter by 24 inches deep unless approved (1113.1.2). Their discharge piping needs a gate valve and a full-flow check valve, except that one- and two-family dwellings need only a check valve (1113.1.4). Storm water must not drain into sewers intended for sewage only (1101.3).

Backwater valves (IPC 714)

• 714.1: where plumbing fixtures are on a floor whose finished floor elevation is below the elevation of the manhole cover of the next upstream manhole in the public sewer, those fixtures must be protected by a backwater valve in the building drain or the horizontal branch serving them. Fixtures on a floor above that manhole cover elevation must not discharge through the backwater valve.
• Exception: in existing buildings, fixtures above the manhole cover elevation may discharge through a backwater valve.
• 714.2: backwater valves meet ASME A112.14.1, CSA B181.1 or CSA B181.2.
• 714.3: backwater valves must be installed with access to the working parts.
• 1101.9: storm drainage systems need backwater valves on the same basis.

Why upper floors stay out: if the public sewer surcharges and the valve closes, upper-floor fixtures that drain through it would back up out of the lowest fixtures. Keeping them on a separate gravity line lets them keep draining.

The trigger is the finished floor elevation, not the flood level rim of the fixtures.