Larch, You may be interested in this.
Below Grade (ground) Bathrooms
Nearly all residential plumbing systems rely on the force of gravity to supply incoming water and to provide for the discharge of waste. But there are times when gravity will not do the job.
Occasionally, a fixture needs to be installed below the nearest available sewer or septic line, and the waste from the drain must be lifted to the level of the main drain.
An ejector pump must be installed to accomplish this. Ejector pumps are required where wastewater cannot flow to its destination by means of gravity at a velocity of at least 2 feet per second.
There are two basic types of ejector pumps.
One is the vertical suspended type where the motor is mounted on the cover of the basin, supported by its shaft connected to the pump housing inside the basin.
The second type is the close-coupled submersible, where the motor is connected directly to the pump housing and impeller by a short shaft and is submerged completely inside the basin.
Submersible wastewater pumps were first introduced in the U.S. market from Europe in the mid-1950s. They became popular in the early 1960s when a guide rail system was developed to lift pumps out of well pits for easy maintenance and repair.
There are two classes of submersibles, the smaller unit, used in home and light commercial applications, and larger units for large commercial buildings and municipal wastewater systems.
Residential units normally handle up to 2-inch spherical solids and range from 1/3 to 2 horsepower. They are commonly called sewage ejectors.
Sewage ejectors are available in two types, non-clogs and grinders.
Non-clogs have the ability to pump high volume and can handle solids from 2 inches through 4 inches and are used both in residential and municipal lift stations.
Grinder pumps grind solids instead of passing them. They are sized only for residential or small commercial locations, often pumping to a pressure sewer system but also in gravity sewers with high vertical lifts or long horizontal runs.
The farther the distance the waste must be lifted, the more powerful the pump must be to do the job. The distance of lift in feet is referred to as 'head'. Head being a unit of measure equal to the vertical pressure exerted by water at one-foot increments of depth.
The size and capacity is also determined by the application. A whole-house system must be larger and more powerful than one that services only one toilet.
By design, larger units will also be able to carry larger solids. Depending on the impeller design, a 4-inch discharge pump will normally handle spherical solids from 2 inches to 3 inches.
Each manufacturer's literature specifies the maximum solids size that can be handled by a particular pump. Attempting to flush objects that exceed this size or ones that expand in water down a toilet runs a risk of clogging the system.
These systems are generally rated to a maximum temperature of 180 degrees F, which means that boiling water should not be poured down the drain.
Sizing for commercial or industrial applications involves complex formulas, and a professional engineer should design these installations. In most cases, a licensed master plumber should be qualified to design a residential system. There are 3 ways to size a sewage pump. Each method is based on peak flow:
The Fixture unit calculation estimates usage demands of a typical plumbing fixture(s). This method is suitable for residential and small commercial applications.
The Larger Capacity System Chart takes fixture frequency of use into consideration. This method is appropriate for motels, apartment complexes, and large office buildings.
The Population method is used when designing large-scale municipal sewage systems.
In each case, the design must also consider total dynamic head, the highest vertical point, and the size of the basin provided. Regardless of peak flow requirement for a given application, the pump must always be able to provide a minimum velocity of 2 feet per second through the line.
Submersible Wastewater Pumps
Submersible wastewater pumps are the fastest-growing products in the wastewater and solids-handling field.
While single pumps (simplex) are often installed, particularly in a single-family residence, many applications require two pumps (duplex) to ensure continued operation not only if one pump fails, but also to minimize wear on each pump and to provide extra capacity in times of extraordinary loads.
A submersible pumping system consists of the sump basin, the motor-pump assembly, and a system of automatic electrical controls. These controls can be simple or complex, depending on the application.
The drainage line runs into the sump basin, and the ejector pumps it through a check valve into the sewer line that drains with gravity. A vent pipe must also be run to relieve the suction created by the pump.
The installation must conform to local building codes.
The size of the pump will affect its location, but even medium to small ejectors need access for maintenance, and this should always betaken into account. In all cases, ejectors should never be placed in a flood plain, using the 100-year flood standard.
The check valve prevents backflow; without it the pump will keep cycling. A high water alarm is suggested, but it must be wired on a separate circuit to warn of pump failure to prevent flooding. Motors may be either explosion proof or non-explosion proof; an explosion proof motor is sometimes required by code.
Ejector pumps may be installed in wet pits or sewage basins. The sewage ejection system typically sits in a hole made through the concrete slab floor. By installing the ejector beneath the floor, the fixture need only be raised minimally to accommodate the flange and waste pipe.
Some cutting of concrete will be involved in basement through-the-slab installations, and this will add to the cost as well as the difficulty of installation.
Basins are fabricated from fiberglass, cast iron or heavy-duty high-density polyethylene plastic. Cast iron models come with lids of the same material, while polyethylene and fiberglass models have a lid that is molded from high-density structural foam, sealed with pressure sensitive foam gaskets.
Nearly all residential models are pre-drilled with inlet holes and a Schedule 40 PVC hub adapter that receives standard 4" Schedule 40 PVC or ABS sewer pipe. Most residential pumps have standard 2" NPT discharge outlets, with 3" discharge optional on some units. Our most popular model is the Zoeller model 266 (shown above).
As drainage pipes flow into the basin, the fluid level rises and triggers the float switch which then engages the pump and lifts the sewage up through a check valve into your regular drain line, much the same as in a sump pump. The water cools the motor naturally, adding to its life span. Field service is simple and sure. And submersible manufacturers report that fewer than one-half of one percent of the pumps they ship are returned for replacement.
Good luck, Tom