Installing Non-Return Valves

non-return valve nrv

Non-return valves, allow residents to prevent rats from entering their properties via the sewer.

Non-return valves or NRVs are made from plastic, metal or a mixture of both. Stainless steel has proved to be the best material (we don’t like plastic).

We’ve used many different types of non-return valve over the years, and we have one in particular that we use day in day out, that we know and trust to work exceptionally well.

Fitting Non-Return Valves

When deciding to have a non-return valve fitted, we need to consider a variety of essential factors.

Factors to consider when installing non-return valves include:
Chamber Access
Chamber Ownership
Chamber Depth
Chamber Integrity
Channel Access
Channel Integrity
Pipe Diameter
Tool Selection
When Rats Won’t Leave
Chamber Baiting

Chamber Access

Access sounds simple enough, but don’t imagine for a second that it’s always as easy as it first seems.

Many of the chambers around a building will be concealed beneath gravel driveways, paths, vegetation, patios, artificial grass, ponds, extensions, boundary fences, walls, parked cars, caravans, and the list goes on and on.

You need to locate the chamber that is closest to the main sewer because it will be the chamber, that once fitted, an NRV will isolate the greatest possible proportion of drainage associated with the affected property.

Shared Chambers

We know, in most cases, shared chambers will belong to the water authority, they will not belong to you.

Water authorities don’t like having non-return valves fitted in shared chambers because very often the non-return valves are installed incorrectly or are not tethered correctly to the chamber wall.

Tethering the NRV requires that you fix a supplied steel wire or cable to the chamber wall, preventing any slippage of the non-return valve downstream of the chamber and We recommend an SDS drill for drilling into the walls of most chambers.

Tethering the NRV ensures that in the worst-case scenario, a non-return valve can usually be retrieved from the pipe if it becomes blocked or jammed.

Utility companies don’t like having non-return valves in the drains because if they try to complete a camera survey, the camera will go through the non-return valve but as you can imagine it won’t come back because the non-return valve will jam against the camera head.

Most drain camera heads cost between £1000.00 and £3000.00 each, with some of the more advanced systems costing up to £10,000.

One great way to get around the problems of a shared chamber or a chamber that doesn’t belong to you is to have a chamber fitted between the main chamber and your property.

We describe this new chamber as an intercept chamber. Having full access to your property and its drains via your own dedicated inspection chamber

It makes life much easier for you and means drains attached to it will be in-line so that you can fit a non-return valve very easily.

A shallow chamber might only cost £300 to £500 to have fitted, or a £1000+ for any chambers deeper than that.

Chambers are an often expensive but necessary investment because fitting a non-return valve is far cheaper than digging up drains beneath your home.

The best solution is always to repair redundant, open or faulty drains. but

However, these drains are often built over, and that means ripping up floors in your house.

Many homes we visit will have expensive floor coverings: timber, vinyl or even tiled and stone floors.

Ripping up floors means your going to need to replace surfaces and new surface coverings or patches will not look the same.

This creates a real problem because it means you’ve either got to put up with non-matching tiles and floor surfaces or have the entire room re-floored.

One other thing that you also need to consider when laying new floors is the height of your kitchen units and the height of the plinths at the base of your kitchen units.

Sometimes the new floor surface will no longer allow these items to fit, so costs will need to account for adaptation to the unit’s height.

For this very reason, it is far cheaper sometimes to have an inspection chamber installed in your property or outside your property between you, and the main sewer and an NRV fitted.

Inspection Chamber Depth

Fitting non-return valves works particularly well when fitted into shallow chambers because you have nice and easy access into the chamber.

When I say a shallow chamber, we’re talking of depth of no more than three feet.

The reason I say three feet is because that’s approximately the maximum arm’s length. Anything over that and you may well have to fit yourself inside the chamber and chambers in most cases are not really built for us to crouch down inside.

Inspection Chamber Integrity

Although we might imagine that a chamber will be in good order, we often find severe failings within chambers that are responsible for the rat ingress issues.

There are at least twelve different ways that rats can escape a chamber into your home.

If the chamber is in poor condition, we strongly recommend a technical drain inspection by a professional drain company. The last thing you need is to get trapped, injured or even killed in an inspection chamber.

Channel Access

Another issue that we have with non-return valves is the benching.

Occasionally benching (smooth cement sloping into the main channel of an inspection chamber) overlaps the side of the central channel that runs through the chamber, preventing a non-return valve from being fitted.

Grinders are easy to buy from most stores. You can buy 18 V or cable or wired grinders for £40-£50, but these again can be quite dangerous if you’re not familiar with their use.

Lateral branches extending past the benching, into the channel will also cause obstruction when you are trying to fit the NRV.

Sometimes the lateral extension can be trimmed or modified with a grinder or some other cutting implement.

Channel Integrity

On many different occasions, we have found ourselves unable to proceed for the following reasons: the channel has been blocked with debris, is displaced, damaged, or isn’t even visible because the chamber is full of sewage caused by a possible collapse or other obstruction.

It makes no difference how competent, determined or frustrated we are, because if the channel is defective, then the NRV is never going to fit effectively.

Pipe Diameter

The sewer pipe is going to be either 4 inches or 6 inches. Sometimes the pipe is larger, and in rarer cases, it could even be smaller, but NRV’s are only available for 4″ and 6″ pipes.

We find that most plastic pipes easily accept NRV’s, but clay pipes can vary by just a few millimetres, and that can spell disaster for a comfortable fit.

The problem with pipes being a different size is that you will need to modify or adapt the non-return valve to fit correctly, and this is easier said than done.

We use a portable grinder, which we carry with us as standard. We can adapt the stainless steel and custom fit the valve, but if you are using this on drains yourself it can be a bit more complicated, so please bear this in mind.

If you fit the NRV into a clay pipe, then in one in twenty cases you will probably be fine.

In about one in twenty cases, it won’t fit properly. If the valve is catching on something in the pipe, you can turn out the bottom wings of the NRV by just a few millimetres using some pliers and enable a smooth, clean fit.

Tool Selection

There are many tools we take with us on every single NRV fitting job that be useful to detail here.

18V SDS drill – drills holes in just a few seconds
18V Driver – to rapidly drive screws in
18V Angle grinder with a masonry disc – for benching and more
Half face respiratory protection mask
Eye protection
7mm wall plugs
40mm no-rust screws
25mm stainless steel washers
7mm SDS masonry drill bit
150mm zip ties
Disposable gloves
1.8m x 1.8m groundsheet – keeps you clean
Knee pads or knee rest
2 x 18inch flat head screwdrivers
14inch crowbar
18inch pry bar
Various chamber lifting keys
Portable grinding/sharpening unit
Disposable rubbish sacks

Odour Control

Another issue that people tend not to think about is the smell.

A non-return valve will fit very quickly and very easily into most drains, and it will prevent the flow of rats, but one thing it won’t do is prevent the flow of air.

If you do have a drain fault, then you might be used to a weird or foul smell within the property at certain times.

These times tend to coincide with heavy rain or when people are using the sewers, especially in the evenings when people are coming home from work and having baths, washing up and doing their laundry, etc.

This is when the water level in the sewers rises, forcing dirty air in the sewers up lateral branches, into rooms above open, via redundant drains beneath your floors.

When Rats Don’t Exit The NRV

Most adult rats will go through a non-return valve to the main sewer and course they will not be able to return to the main sewer.

Problems arise with juveniles or sub-adult rats. Young rats will not always want to go through the non-return valve.

As a result, you can end up having rats remaining in the system. It’s therefore vital that whenever you have an NRV fitted, you fit the non-return valve to the exit branch of your inspection chamber.

Baiting a chamber fitted with an NRV in this manner will allow you to bait effectively and exclusively the rats in your system, refusing to go back through the non-return valve. Very quickly it will sterilise your house of rodents effectively and permanently.


Now let’s look at the worst-case scenario.

You’ve identified a drain fault, or you suspect a drain fault.

You’ve had an NRV installed correctly, and the chambers are baited. So you know hand on heart that you no longer have rats in your drains – “but you still have rats!”.

When non-return valves fail to solve a rat problem, the rat problem is almost certainly connected with the neighbouring property or with redundant and unmapped drains.

These drains will rarely show on maps. We see this most commonly with properties built on residential land following the Second World War.

You won’t see the flattened or derelict houses above ground, because they were cleared away decades before. Sadly, you are also unable to see the redundant, legacy sewer system below the ground.

Many of these sewers are still connected to the active sewer network but no longer mapped. Rats use these discarded drains as a safe highway to access properties that have no obvious access points above ground or via their own, mapped drains!

This is why it’s so important when you buy a property that searches offer an indication as to whether or not your property was built in an area that used to have bombed-out buildings, factories or other structures that would’ve once connected to the main sewer.

A final word of advice given to all our pest control customers.

When we carry out a drain survey, we often charge a little more or significantly more than other providers because there are a couple of things we have learnt over many years of investigation.

First, you need to consider any building to which you are attached as one single unit because rats can come in at any point under or around that building.

Sometimes we need to check multiple drains in multiple properties.

Imagine for a moment that you have a semi-detached house. We would consider checking the drains on both sides if necessary to be sure that the property is completely isolated from any drain fault.

The next thing that you need to look up is the likelihood that any insurer or third party carrying out inspections will have the specialist competence to identify the root cause of your infestation.

The contractors we routinely see, fail surprisingly often, not because they are incompetent but because they lack the specific knowledge that only a pest controller who does regular drain surveys will have.

Rats can get through a gap of just 10 mm. In many drain surveys, we will see gaps of this size or larger, meaning that in some cases what’s needed is that the faulty drains need to be lined or patched.

Lining a drain is typically done in long sections of a metre or more. Patching is where they line a pipe but in smaller sections of a metre or less.

But of course, these measurements are approximate. Every drain company will have its standards, and every industry body may have their rules as to what is required and necessary in those situations which is why we leave those particular situations to drain engineers to decide how they want to proceed.

Being a specialist is as much about knowing when to step back as it is knowing when to step up.

We always endeavour to be fair and honest with our customers and say that in situations where we lack the expertise to complete works fully.

Our ambition is to put them in contact with people who have the requisite knowledge to competently and effectively remediate the issues we find.

The most challenging issue of all is where we have contractors coming to do work, most commonly through an insurance company, claiming they’ve done repairs and they haven’t.

Alternatively, they say they’ve done repairs, but haven’t done them as robustly as necessary, or the repairs are carried out are in the wrong place, and they’ve repaired the wrong thing.

One reason we believe that this is so common is that nobody ever expects a pest controller will go in after them and check the repair has been done competently, but we do. Thinking you’ve fixed the problem is only part of the story.

The concluding part of any story is knowing that it’s at an end, and a final inspection of the drains by ourselves gives us complete clarity, understanding and confirmation that the problem or the issue that we have identified has now been fully resolved.

Non-return valves and any drain repair is only ever a test that allows us to identify and prove whether or not an identified problem is indeed the source.

Final inspection and confirmation rule out any future likelihood that it could be the problem.

Most rat infestations require a multi-point solve, and you need to evidence and never celebrate a victory until at least 30 days after a final repair has been completed.

We find in most cases that 30 days after a full repair has been completed, if no rat activity has been heard, it’s almost certain that the customer will never, ever have another rat problem in their homes.

But that 30 days is critical, absolutely critical to the peace of mind of the customer and yourself or any pest controller or drain contractor to have a level of certainty that the problem is gone for good.

Get Help In Bristol – See The Bristol Rat Company

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