Common Problems Found in Gravity Sewers

One of the great myths about vacuum sewers is that they have more operational problems than traditional gravity networks. This is simply not the case. Certainly if something bad occurs in a vacuum system, like a blockage, the operator is notified quickly via alarms; he finds the problem quickly and solves it without the homeowners being adversely affected or overflows occurring.

Gravity sewers though are prone to things going wrong for years and years without operators becoming fully aware until sewerage is flowing down the streets or onto the beach.

Although the decision makers like to think that gravity sewers are easy to maintain and don’t have problems, we thought it worthwhile to explore some of the main problems that operators of sewerage networks come across during the course of their day versus what the operators of a Flovac vacuum system may find.

Items Gravity Sewer Network Flovac Vacuum Sewerage System
Fats, Cooking Oil and Grease (F.O.G.)
  • As FAT, OILS and GREASE cool down in the sewer, they slowly coat the walls of the sewer lines and eventually build into a thick wall that dramatically reduces the flow of sewage and eventually creates blockages.
  • These blockages are very expensive to fix and become a burden to the city and a cause for added maintenance costs and rates..
  • Occasionally, sewer lines are flushed with the help of huge flusher trucks, but this is hardly a solution, as the high pressure dislodges large blocks of F.O.G. that then find their way to the sewage pumping stations and create other mechanical problems down line.
  • Abundant F.O.G. becomes a smelly pollutant that, when mishandled, can easily find its way to our beaches and waterways where it becomes a hazard to fish and other marine
Flovac has developed a unique FAT FREE© system to allow for vacuum systems to easily handle any fats, oils or grease.The velocity of the sewerage entering the vacuum pipework is greater than 5 metres per second. This is followed by a large quantity of air entering the system at greater than 100 metres per second. This creates a scouring of the pipes which does not allow for any build-up of fats to generate.

Flovac’s R&D group has done extensive study on the fats entering the system and the impact they can have at the collection pit and valve in particular. A change in the existing process (patent pending) can show an elimination of problems related to fat build up.

This does not suggest that these items can now be put down a sewerage system as problems at the treatment plant process still exist. But the maintenance problems are certainly reduced.

Nappies/tampons/condoms Yorkshire Water reports the following blockage rates in their gravity sewers38.43% caused by fat, oil and grease
11.96% caused by nappies/wipes/sanitary products

Nappies cause major problems in gravity lines and all items cause problems at the pump station with maintenance.

The velocity of the water and air movement in the vacuum mains causes all of these items to be shredded very finely.To pass most national standards related to vacuum valves, these items must be able to pass through.

If you would like to see the Flovac video of these, and other items, going through the system, please contact us.

It is important to only use 90mm/3” vacuum interface valves when dealing with municipal sewers.

Children and dogs Small children and dogs can be trapped in sewerage pipes. Although the Flovac valve has the largest internal diameter of any vacuum valve on the market at 78mm (3”) it is too small to allow for children or dogs to enter the network.
Children’s Toys Toys can easily get blocked within the sewer mains –usually at the most inconvenient point -15 metres under a major highway or creek. Odd shaped toys have occasionally blocked the valve but our easy screw top body allows for them to be easily taken out.The valve can be easily located and the valve will still block partially open allowing sewerage to still flow into the system.

We have never had a blockage in a vacuum main –as if it can fit through the 3 inch valve it will fit into the smallest part of the piping network.

Alligators and Snakes A common problem in some places (particularly New York) as well as snakes in others. This leads to particularly nasty consequences for some of the operators. Alligators cannot fit into the Flovac vacuum system and snakes find survival difficult with the negative pressure and high velocity.
Sand and cat litter Many sewers get blocked by sand build up in coastal areas. Most vacuum systems are located in coastal areas so must prove in the standards that they can cope with sand and gravel. The design of the Flovac vacuum pit set up ensures that sand quickly enters the vacuum mains and does not remain in the pit causing problems.
Clothing including underpants Clothing entering the system causes big problems at the sewage pumps which increase operating costs. Clothing can also cause blockages in the pipes if fat and grease are also prevalent. The velocity of the water and air entering the system shreds all clothing into small fibres. We have never had a blocked pipe or valve due to clothing. Only 3 inch valves should be used.
Rats, mosquito’s and other vermin Rats are often found in sewers, in some countries in plague proportions. Rats and mosquito’s spread a number of diseases. Flovac vacuum systems are closed systems, rats cannot enter the system and there is no open sewage pooling that would attract mosquitos.At one project where septic tanks were replaced it was found that the health of the town improved significantly due to the installation of a Flovac system. The local mosquito population virtually disappeared overnight.
Clowns In the US it is quite common to find clowns entering the sewerage system to scare small children. This can cause traffic problems. Our R&D group have donned clown masks and tested our systems to ensure that clowns cannot enter the system. They found that the pipes sizes used in vacuum sewers are too small to allow clowns to enter the system.
Sewerage System Operators Operators around the world constantly need to enter gravity sewer pipelines and wet wells. Gases are a common problem which can lead to explosions and death, gas testing must first be done. Within the sewers, bad odours and dangerous conditions are prevelent and many cases of deaths and injuries have occurred over the years.Gravity Sewer Operator in Australia The Flovac system is loved by operators as there is no interface with raw sewerage. The pipes are small and operate in a closed network. Overflows do not occur and valves are usually located separately to the sewerage sump.FLOVAC Vacuum Sewer Operator