FREQUENTLY ASKED QUESTIONS
We’ve compiled a list of the questions we get asked the most often. To jump to the section you’re most interested in, simply click on one of the tabs directly below.
Manholes have a better chance of sucking air into the sewer system than vents on houses do because the manholes are closer to the power of the water flow and create a much stronger vacuum. (Imagine adding 50 feet of pipe to a home vacuum cleaner and the resulting dramatic loss of suction.)
Also, because gases rise to the highest level they can find, if you don’t vent manholes, you can still get gas deterioration because gases will accumulate. (Of course, manholes also need a way to stop rainwater from getting into your sewer system, which the Sewer Sentry also does.)
Yes. Due to the reduction of inflow there is less surcharge of the system during rainstorms. This deters SSO’s as well as flooding of homes and businesses.
This category of products exists because every city that gets rain has problems with inflow through manhole lids. However, we have designed the Sewer Sentry to provide some benefits not seen in other products:
- The Sewer Sentry does not have to be tethered to keep it from falling into the manhole.
- It does not have to be removed to allow access to the manhole.
- The Sewer Sentry does not have a pressurized valve to release gases. Instead, it provides an open hole that reduces the ability of the gas to accumulate at any time without the need for pressure build up.
- It creates a pick hole that enables easy access.
The Sewer Sentry adds ⅝” height to the profile of a manhole cover.
Your sewer systems are already vented to some degree, or they would not work. That is, some sewer gases are already escaping your system, probably through a small number of vents that concentrate the odor in a few spots in your town or city.
Installing Sewer Sentries throughout your system allows gases to be distributed not in a few powerfully concentrated areas but in much smaller concentrations over a much broader space.
This is the same effect you would see if you took a five-gallon bucket of mothballs, which you could easily smell at a distance, and spread them out over a one-mile stretch, diluting the smell to nearly nothing.
Additionally, the extra oxygen that Sewer Sentries allows into your sewer system reduces the production of methane and hydrogen sulfide, which require an anaerobic environment for their creation. Adding oxygen through venting ensures that the gases won’t reach levels that are obnoxious to your community or corrosive to your sewer system.
Above-ground manholes still need to be vented to lessen corrosion due to the presence of hydrogen sulfide gas and to lengthen the life of the sewer system by letting oxygen into the pipes.
Additionally, the inflow report* by the Neenah Foundry Company shows that even a splashing rain on a 24” manhole lid with one just 1” hole lets in 4.34 GPM.
This means that a town that has 400 manholes that are raised above ground can still expect an inflow of 416,640 more gallons of water during a four hour rainstorm. A city with 2000 manholes can expect 2,082,000 more gallons.
The more storm water you stop, the less you will pay for pumping and treatment as well as repairing flooded homes and cleaning up SSOs.
* Neenah Foundry Company, “A Report on Inflow of Surface Water through Manhole Covers,” date unknown. http://www.nfco.com/municipal/engineering-literature-videos/pdf/report-inflow-brochure.pdf. Accessed April 10, 2014.
The Sewer Sentry can be equipped with a brightly colored pipe however high you want to indicate the position of the manhole and to prevent storm water from entering the Sewer Sentry’s one-inch diameter hole.
The Sewer Sentry can be equipped with a check valve system to prevent an overflow through the vent hole.
If a manhole has extra holes that you don’t want to outfit with Sewer Sentries, you can glue one-inch thick rubber plugs in them, using the same glue used for installing the ring and cover gasket. The rubber plugs can be produced from a one-inch thick piece of black rubber, which you can easily find at any rubber supply company. Black rubber should be used to provide UV resistance. The plugs must be made on site so that you can measure the size plug needed for each hole, because the holes could be slightly different diameters.
Most pumps will pass three-inch solids. The nut on the bottom of the Sewer Sentry is smaller, only 2 ½” X ¾”. Additionally, the rubber gasket that’s between the mushroom-shaped insert and the nut of the Sewer Sentry will serve as a locking device. If you are still concerned, though, you can put thread lock on the threads of the mushroom-shaped insert to secure the nut.
- 3 ½” wide at top
- 2 ⅝” wide at bottom
- 2 ⅞” high
- Rises only ⅝” above manhole cover
Yes. Most sewer systems have main lines, called trunk mains, that carry more sewage than smaller lines but don’t have any services. The only way that they are vented is from manholes. In these manholes, you might need more than one Sewer Sentry to adequately reduce the concentration of hydrogen sulfide.
No. The rubber will absorb the shock and keep the lid from bouncing.
Our best guess is that only 2% or 3% of the manholes in a typical system should be routinely hit by traffic. The rubber is engineered to be hard enough to take abuse from traffic and soft enough to seal from the weight of the manhole lid. The rubber gasket should give you years of life and is easy to replace when the time comes. Additionally, since it will prevent the ring and cover from rusting, it will save ring and cover replacement costs in the future.