sewer blowback

Sewer Blowbacks –Releasing the pressure!

Sewer Blowbacks – Releasing the pressure!

What is a Sewer Blowback?

A sewer blowback is when a combination of air/water/wastewater is ejected from a household wastewater fixture, such as a basin, floor drain, gully trap, and, most commonly a toilet.

This can occur when routine or reactive maintenance is being carried out on the utility’s sewer network with high-pressure water
jetting equipment. Water jetters are used to clear roots, debris and blockages in the sewer system and ensure flow occurs uninhibited. 

Blowbacks occur due to difference in pressure in both the main sewer line and the attached house plumbing. When jetting equipment is in use, water is forced into the sewer main under high pressure, this requires the displacement of a similar volume of air. The space behind the jetter is an area of high pressure, while there can be a negative pressure zone in front of the jetter nozzle. In most cases this air is forced along the sewer main or out private property vents. However, if there is insufficient ventilation, or a blockage in a house vent, this pressure will move to take the path of least resistance. This can result in pipe odors rising through floor drains, and if there is enough positive pressure the water seal in the toilet bed can be blown with force out of the fixture. 

The inverse of a ‘blowback’ can occur where negative pressure occurs in property plumbing, and the water seal in fitting bends can be sucked out, resulting in an atmospheric opening to the sewer causing the odour from the sewer to flow through the fixture into the room that it is located. In these cases, it can be rectified by adding additional water to the water seal 

sewer blowback process

Why do sewer blowbacks occur?

There are two factors that can be attributed to a sewer blowback within the property drain itself. 

A drainage vent can become blocked or restricted over time which can increase the likelihood of a sewer blowback. 

Blockages within the sewer main can also cause water to build up on the upstream side of them; when the jetter nozzle goes past the property connection the water can be forced up the connection pressurizing the property drain unless it has somewhere to go. 

sewer blowback

How can we prevent or minimise sewer blowbacks happening?

 There are several factors that contribute to sewer blowbacks that happen during the cleaning of the sewer main, some can be minimised/mitigated, and others cannot. 

  1.  Communicating to property owners that sewer main cleaning is scheduled, and it is recommended that they keep toilet lids closed. 
  2. Opening the upstream manhole to allow additional flow into the main being cleaned. 
  3. Using lower pressure and/or flow from the jetting truck.

    Most blowbacks consist of only the contents of the water volume within the trap/water seal and is usually clean water that is replaced on a regular basis by flushing the toilet and running a tap. Some utilities will keep a blowback register of historical occurrences. It is recommended to contact them if this happens to help inform future maintenance programs and minimise the potential of it happening again.  

     

About the author Anthony Woodhouse
lateral sewer pipes

Thinking laterally – Can lateral inspections supplement your inspection program?

Thinking laterally – Can lateral inspections supplement your inspection program?

The majority of any pipe network is made up of the smaller diameter lateral connecting pipe lengths (relative to mainline lengths), so it’s no surprise that lateral inspections are becoming more and more popular.

Let’s take a look at what you need to know about lateral inspections.

lateral sewer pipes

What are lateral inspections?

Lateral inspections are inspections that survey the connecting pipe to the main line. The inspection can either be done from an access point upstream of the connection back down to the mainline or from the mainline up through the lateral connection to a connection point or boundary point upstream.

Depending on where in the world you are, these connecting pipes to the main line are sometimes called house branch connections, junctions or taps. Similarly, there are also varying ways to undertake a lateral inspection or coding defects associated with the lateral. Some countries include lateral condition coding with mainline condition coding, whilst others treat the lateral condition coding separately.

Why are lateral inspections required?

Water authorities will do lateral inspections for several reasons. Most organisations undertake lateral inspections in their network because they own the lateral and are therefore required to maintain all or part of the lateral length. There are some organisations that proactively undertake lateral inspections to investigate unknown connectivity of the network.

When should I do a lateral inspection?

Funding an inspection program can be challenging sometimes. So, adding lateral inspections to your inspection program might sound like an extra burden. Let’s look at some of the reasons water authorities choose lateral inspections for their inspection program that make the investment worth it:

  1. Investigating reported customer issues – if a customer reports an issue and no problem can be identified with the mainline pipe.
  2. Investigating network connectivity – if there are suspected illegal connections in the lateral network, or if th
  3. As a workaround for upstream access restrictions

All of the above challenges cost the water authority’s money if left unresolved, which makes the business case for lateral inspections much easier. The magnitude to which this impacts your organisation will drive a cost-benefit ratio that makes sense for your organisation’s circumstances.

lateral inspection launch

Minicam lateral launch

How can I get a lateral inspections done?

Depending on the reason for the inspection, and that site access conditions, lateral inspections are usually undertaken in one of two ways.

  1. Starting from the mainline – The first, is from the mainline using specialist inspection camera technology. This involves a type of camera that has ‘lateral launch’ functionality, which basically means a camera can be ‘launched’ up the lateral up to a length of 150 ft or 45.72 meters.  There are restrictions on the use of these types of cameras, such as lateral and camera angles. This type of inspection can help with access issues, and investigations of network connectivity.
  2. Starting from an upstream point in the lateral – The second way to do an inspection of the lateral starting from an upstream point in the lateral down towards the mainline. Its possible to do this type of inspection with a standard CCTV inspection camera (either crawler or pushrod). This type of inspection can help with investigations of customer issues.

Conclusion

The increased demand for lateral inspections can be attributed to a number of things, not least of which the availability of the technology, and increased customer reporting capability and more. Either way, these inspection methods are a great way to supplement your upcoming inspection programs where the needs arise.

About the author