In the Academy Award-winning movie “Forrest Gump,” the titular character has been immortalized by his comment, “Life is like a box of chocolates. You never know what you’re going to get.” As true as this statement is about life, I find it even more accurate when entering public restrooms. I usually just pause for a second, hold my breath and hope for the best. Will it be clean or should I be wearing a hazmat suit?

Besides the tendency for these facilities to look unclean and terrorized by previous users, perhaps the more concerning issue is the smell. In the cases where your sense of smell is abused, often the problem can be attributed to what I might call “user misuse,” but in many cases the offending odor is the result of a lack of a trap seal in the floor drain. If we are honest, we all know that public facilities are not always maintained properly, but with proper maintenance and the use of trap primers, these and other floor drains do not have to be the culprit for unsanitary and unpleasant conditions.

The requirement for fixtures within the building to be trapped by a water seal (see Figure 1) has been in plumbing codes for almost 100 years. The trap’s main purpose is to eliminate the possibility of sewer gas from entering the confines of the room or building. The water seal, or trap seal, effectively accomplishes this by creating a barrier of between two to four inches of water that prevents sewer gas from entering the room. A secondary benefit is that it prevents access of pests or vermin to drains, as well as access to the building through the fixture by way of the sewer system.

Floor drain traps that do not connect to a water-supplied fixture will tend to evaporate. Other traps that are not periodically used or are installed in overly dry areas also will lose their seal by simple evaporation. The result of this loss allows known health hazards such as hydrogen sulfide, methane, bacteria, viruses and mold to enter the living space. The SARS epidemic (Severe Acute Respiratory Syndrome) reported in Hong Kong in 2003 was caused in part by a dry and leaking trap, and has raised the awareness of the dangers of an unprotected sanitary drainage system.

One of the first lines of defense against trap failure is the trap primer, which is a piping device that helps to maintain a water seal in a remote trap. A trap primer connects to a cold water inlet or other water supply. Every time that inlet or supply is used, a small amount of water flows down to the trap to keep the water seal from drying up. If the primer is electronic, it is set on a timer that daily releases enough water to maintain the trap seal.

It is clear that traps can easily dry up in rooms where floor drains are seldom used, but it may not be obvious that traps dry up in rooms that are used daily. This is a common problem in mechanical and service rooms, which are often dry and overly warm. Years ago, traps would be regularly replenished on the janitor’s nightly rounds. Enough of the soapy water from those old fashioned heavy mops would go down the floor drain to replenish the trap. Today, with the popularity of dry chemicals for cleaning, not much water is used on the floors, at least not enough to keep the traps seal full. By providing a trickle of water every time water is used, trap seal primers refill the seal of a P-trap.

Making the correct choice of which trap primer to use should take some thought. There are three main kinds of trap seal primers:

  1. Pressure drop activated.
  2. Flush valve operated.
  3. Multiple and electronic activated.

Pressure-drop-activated trap seal primers are usually brass, have a one-half-inch male iron pipe inlet connection, and one-half-inch female iron pipe outlet connection. An interior cartridge seals when the line pressure is in a static state, but when the line pressure drops just three psi by the flushing of a toilet, or an opening of a faucet, etc., the cartridge will rise. It rises because a pressure differential has occurred within the primer. At this point, a metered amount of water is discharged under pressure into the line connected to the floor drain trap.

Pressure drop activated trap seal primers are designed to minimize the problem of clogging. These trap seal primers are constructed with a fine mesh filter, keeping line debris at bay.

The flush-valve-operated trap seal primer gets its name from its installation. It is placed below the flush valve on a water closet or urinal and connects to the floor drain by a tube so that the tube can catch some of the water discharged from the flush valve. The water runs down the tube to the floor drain and the water seal is maintained. This trap seal primer has two positive features: 1.) low water consumption since it only uses a portion of the discharged water from the flush valve operation, and 2.) no moving parts. However, this trap seal primer also introduces some restrictions. Its use may not be practical because the flush valve may be situated too far from the floor drains. In this case, a pressure-drop-activated trap primer is more practical since it can be installed close to the drain that needs to be primed.

When a number of pressure-drop-activated trap seal primers are located close to one another, they can be primed via a multiple trap primer. In this case, a metered amount of water from the trap primer is evenly distributed to more than one floor drain trap by means of a distribution unit or an electronic primer manifold. For every 20 feet of floor drain trap make-up water line, the primer must have a minimum of one foot elevation from the finished floor. It should generally be mounted level with the water supply line.

These multiple units can be installed in a variety of situations. For example, such a unit is useful when a men’s restroom is located next to a women’s restroom. In this instance, one trap seal primer can serve both floor drain traps, omitting the need for additional trap primers, extra shutoff valves, another access door and air gap fittings, which saves time, money, and labor. They can also be installed with an electronic timer to provide automatic filling of the trap seal. In this installation there is no worry about having enough pressure drop or use of the fixtures to keep the trap filled.

The trap primer must be accessible. The access door needs to be large enough to allow the plumber to reach the trap seal primer, the line shutoff valve and any other accessories present. Installing a line shutoff valve will make repair and maintenance that much easier.

 Life, people and the places you go are, indeed, often unpredictable. With the proper use and installation of traps and trap primers, that unpredictability is limited.  


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