3.3 Sewage Ejectors, Sumps & Macerating Systems

3.3 Sewage Ejectors, Sumps & Macerating Systems

When plumbing fixtures are installed at an elevation below the crown of the public sewer main or on-site disposal invert, gravity drainage is impossible. Forcing gravity drainage in such conditions would create a permanent backflow disaster, where municipal storm or sanitary surcharges back up into lower fixtures. Under Florida Plumbing Code (FPC) Section 712, all drainage below the sewer level must be gathered in an airtight, gastight sump pit and mechanically lifted into the gravity drainage network.

1. Sump & Ejector Equipment Classifications

Plumbing sump equipment is divided into four distinct categories based on the nature of the liquid conveyed:

1. Clearwater Drainage Sumps:
   • Collect subsoil drainage, foundation seepage, elevator pit drainage (with oil separators), and air conditioning condensate.
   • Handled by standard submersible sump pumps; solids capacity is typically limited to 1/4" to 1/2" grit.
2. Solids-Handling Sewage Ejector Pumps (FPC 712.3.3):
   • Mandatory for blackwater waste containing human fecal solids and toilet paper from water closets and urinals.
   • The 2-Inch Sphere Rule: Non-grinder sewage ejectors must be capable of passing a 2-inch (51 mm) solid sphere through the pump impeller and volute without jamming.
   • Minimum Discharge Pipe: The discharge piping from a solids-handling ejector must be a minimum of 2 inches in diameter.
3. Sewage Grinder Pumps:
   • Utilize high-torque rotating cutter blades to shred organic solids and hygiene products into a finely macerated slurry before discharging into the impeller.
   • Because solids are pulverized, grinder pump discharge piping may be reduced to 1-1/4 inches or 1-1/2 inches pressure-rated pipe.
4. Pneumatic Sewage Ejectors:
   • Utilize compressed air injected into an airtight receiver tank to displace sewage upward into the gravity main without rotating mechanical impellers.
   • Primarily used in high-capacity institutional and industrial installations.

2. Basin Construction & Sump Venting (FPC Section 712.4)

Sewage ejector basins collect volatile, toxic, and explosive gases, including hydrogen sulfide ($H_2S$) and methane ($CH_4$). The code strictly regulates sump construction and venting:

• Basin Integrity: Sumps must be constructed of non-corrosive materials (fiberglass, polyethylene, or epoxy-coated cast iron/concrete), placed on a firm level bed, and equipped with a bolted, gas-tight cover sealed with an elastomeric gasket.
• Purpose of the Sump Vent:
  1. Prevents pressure buildup inside the pit when incoming wastewater displaces air.
  2. Prevents vacuum formation when high-capacity pumps rapidly evacuate liquid, which would otherwise pull water out of fixture traps draining into the basin.
  3. Exhausts harmful sewer gases safely above the roofline.

Critical Vent Connection Rule (FPC Section 712.4.2)

The sump vent may terminate independently through the roof OR tie into the building's gravity vent system. However, if tied into a gravity vent stack, the connection must be made at least 6 inches (152 mm) above the flood level rim of the highest fixture served by the gravity system!

   Gravity Vent Stack                                  Sump Vent
          |                                                |
          |                                                |
          +=================== TIE-IN =====================+
          |    (Must be at least 6" ABOVE highest          |
          |     gravity fixture flood rim!)                |
          |                                                |
     [Lavatory] Flood Rim                                  |
          |                                                |
          |                                           [Sump Basin]

• Why this matters: If the gravity sewer main clogs and raw sewage backs up in the building's vertical stacks, keeping the vent tie-in 6 inches above the highest flood rim prevents liquid sewage from flowing across the vent piping and pouring into the sump pit!

3. Valve Configuration & Piping Sequence (FPC Section 712.3.2)

The discharge line of every sewage ejector must be equipped with two distinct valves installed in an exact, mandatory sequence:

1. Approved Check Valve:
   • Prevents the column of lifted sewage in the vertical discharge line from draining back into the sump pit when the pump cycles off.
   • Must be a swing check valve or spring-loaded flapper valve rated for wastewater service.
2. Full-Way Valve (Gate Valve or Full-Port Ball Valve):
   • Installed on the discharge side (downstream) of the check valve to provide positive shut-off.
   • Allows isolation of the sewer main so that the check valve and pump can be removed, inspected, or replaced without draining hundreds of gallons of sewage from the overhead building drain.

The Mandatory Valve Order

$\text{Pump} \longrightarrow \text{Discharge Pipe} \longrightarrow \text{Check Valve} \longrightarrow \text{Full-Way Gate/Ball Valve} \longrightarrow \text{Gravity Main}$

[!CAUTION] The Reversed Valve Violation: Installing the gate valve between the pump and the check valve is an automatic inspection failure. In that reversed position, closing the gate valve leaves the check valve under continuous backpressure from the gravity sewer main, making it impossible to service or clean the check valve without flooding the mechanical room.

4. Connection to the Gravity Drainage Main (FPC 712.3.5)

The physical connection of the pumped discharge into the horizontal gravity building drain is strictly controlled:

• Top-Entry Requirement: The ejector discharge pipe must enter the gravity drain from the TOP of the horizontal pipe through a wye branch fitting or combination wye and eighth bend.
• Prohibited Side or Bottom Entries:
  • Entering from the side (horizontal center-line) causes turbulent flow that disrupts gravity drainage and can siphon fixture traps upstream.
  • Entering from the bottom is completely illegal: gravity solids and sludge flowing down the building drain would settle by gravity into the ejector discharge line, packing it full of solid waste while the pump is dormant.

5. Duplex Systems & Electrical Safety Controls

In public buildings, commercial restaurants, hotels, and multi-family residential facilities, pump failure results in immediate health hazards:

• FPC Section 712.4.1 Duplex Requirement: In public buildings, commercial structures, or installations where two or more water closets discharge into a sump, duplex (dual) ejector pumps must be provided.
• Alternating Controls: An automated control panel alternates pump starts between Pump 1 and Pump 2 to distribute mechanical wear evenly.
• Lag/High-Water Assist: If inflow exceeds the capacity of one pump, both pumps activate simultaneously.
• High-Water Alarm: Sumps must have an independent audiovisual alarm powered by a dedicated circuit to alert building operators of pump failure before sewage overflows the basin lid.

6. Macerating Toilet Systems (ASME A112.3.4)

In residential slab-on-grade remodeling where cutting concrete trenches is structurally prohibited or cost-prohibitive, plumbers may install a macerating toilet system:

• Standard: Must conform to ASME A112.3.4 / CSA B45.1.
• Design: Consists of a rear-discharge water closet connected directly to a compact macerating pump chamber situated behind the bowl. The unit shreds fecal solids and toilet paper, pumping effluent vertically through a 3/4-inch or 1-inch discharge pipe.
• Code Restrictions:
  1. Permitted primarily for single residential bathroom additions.
  2. Cannot be the sole toilet facility in commercial or public occupancy structures.
  3. Must be supplied by a dedicated GFCI electrical circuit.