Plumber's Licensing Exam: Vacuum Drainage Systems

Vacuum drainage systems are beginning to increase in application in areas where water conservation is a high priority. Little attention has been paid to them from a code-writing standpoint because of their specialized nature. We are sure to see more detailed code provisions for vacuum drainage systems as they become more common and perhaps even required for use in buildings in some areas.

Objectives:
- Gain familiarity with vacuum drainage system design
- Identify vacuum drainage system applications
- Explain the importance of manufacturer’s instructions when installing vacuum drainage systems

Key Term:
vacuum drainage system

What Is a Vacuum Drainage System?
Vacuum drainage systems have been in use in airplanes, trains, and other public transportation for many years. The main advantage of vacuum drainage systems in such applications is their compact design and the fact that they are self-contained. Concern about water conservation and legislation are beginning to fuel the move toward adapting some of these systems as permanent fixtures. (Refer to IPC G101.1–G101.4)
In Europe, vacuum drainage systems have been in limited use in buildings for about 40 years. The premium on space has been the main reason for their popularity. Occasionally, special building designs that require no penetrations through a slab floor have necessitated the use of a vacuum drainage system.
Most vacuum drainage systems are capable of lifting waste approximately 15 feet, so waste can be transported in overhead pipes. Drainage pipes can be a smaller diameter in a vacuum drainage system because they have the force of atmospheric pressure ramming the waste through the drainage piping.
This is not a plumbing configuration that most of us are used to seeing. Consequently, following the manufacturer’s instructions to the letter is the clarion call for vacuum drainage system installations. The IPC expressly states that you do so. Even the piping materials used must be those recommended by the system manufacturer as long as they appear in Table 702.1 of the IPC, which lists the materials acceptable for above-ground drainage piping.

Real-Life Situation: Carlos, the owner of Ace Plumbing Company, has another new adventure for his crew. He has just won the contract to service, repair, and/or replace the vacuum drainage system components for all of the Springfield city buses. You get the honor of doing the first one because Carlos has a lot of faith in your work. You must find out all you can about these systems before the job starts to maintain your reputation. You are sure to learn more as you tear into your first system.

Fact: The first vacuum drainage systems were used in Prague, Czechoslovakia, and in the Dutch city of Amsterdam as early as 1882. These early systems were powered by steam engines.
Only about 1 to 11/2 quarts of water are used to flush a water closet in a vacuum drainage system, and that is used mostly for the final rinse and refill (Figure below). At first look, a vacuum water closet does not appear to be much different from a standard gravity water closet. On closer inspection, one will find that there is no tank and only a small push button or a foot pedal for flushing. In the bottom of the bowl you may be able to see the ball of a large ball valve. Some vacuum water closets have the discharge out the back and the ball valve, or in some cases the slice valve, is not visible.


Figure: Vacuum Drainage System Water Closet Function Cycle Cutaway

When the pneumatic button or the foot pedal is pushed, a water valve opens to initiate a rinse of the bowl, and the large discharge valve opens to allow the atmospheric pressure to force the waste and water through the discharge pipe. The bowl refills and the cycle is ready to start again. The water closet is the only special fixture in a vacuum drainage system.


Figure: Pedal-Operated Vacuum Drainage System Water Closet

Caution: The correct installation of a vacuum drainage system depends on the installer carefully following the manufacturer’s instructions. The plans and specifications must be approved before the installation begins and must be followed diligently. Other fixtures drain to a small receiving tank that automatically opens a discharge valve when a predetermined tank level is reached. The water supply fixture unit is 1 for a vacuum-type water closet. There is generally no vent on a vacuum system because there is a positive seal between the fixture and the wastewater. When standard gravity draining fixtures are used, traps and cleanouts are used according to the code.
When a vacuum drainage system is installed, it must be tested by subjecting it to a vacuum of 19 inches of mercury. In operation, the vacuum system will have from 16 to 20 inches of mercury placed on it by the vacuum pump. The fixtures are flushed by air pressure forcing the waste down the drain toward the holding tank at a rate of 15 to 18 feet per second.
Vacuum drainage systems are built for large developments as well as for individual systems. Coastal and lakefront developments, where gravity systems cannot function due to lack of slope or are prohibited because of environmental concerns, are prime areas where vacuum systems are considered.


Figure: Vacuum Drainage System for a Housing Development

Tips:
More information is available online, primarily from the manufacturers of vacuum drainage system equipment. Some of the manufacturers are AcornVac, Airvac, European Vacuum Drainage Systems LTD, and Jetvac, Inc.