Thread: Back flow valve noise

We have a "whole of house" rainwater system with an isolation value and a back flow valve at the front of the house connecting to the mains water supply. At the back of the house we have another isolation value and a separate back flow device that is connected to 32mm back "plastic" pipe, then to the pump and tank. The isolation values/back flow devices were installed by a plumber about 9 months ago.

Recently we have had a loud humming noise from the pipes when we are connected to rainwater and a slow flow of water is used, e.g. filling the toilet, the dishwasher or turning a tap on slowly. The sound travels through the copper pipes and can be heard throughout the house. As far as I can tell the noise seems to be coming from the back flow valve. Is this possible or likely. Can back flow valves be serviced or are they just a replacement item?

Are you sure that it isn't coming from the pump?

Re your copper pipes, are you also getting any blue/green stains on your basins etc?

Non return valves often whistle and hum. Particularly if something is partially obstructing them or getting in the water flow.

They can be serviced - all they often are is a spring retainer and a ball or flap. Usually one end can be opened for disassembly.

Another option is to mechanically isolate the valve from the house using a flexible quick connect or similar that won't propogate the resonance through the pipework.

Originally Posted by Danny

Are you sure that it isn't coming from the pump?

I am reasonable sure it is not the pump. It is quiet down by the pump and there is 20m of black plastic pipe between the pump and the house.

Originally Posted by Danny

Re your copper pipes, are you also getting any blue/green stains on your basins etc?

No stains on any basins.

Originally Posted by SilentButDeadly

Non return valves often whistle and hum. Particularly if something is partially obstructing them or getting in the water flow.

They can be serviced - all they often are is a spring retainer and a ball or flap. Usually one end can be opened for disassembly.

Another option is to mechanically isolate the valve from the house using a flexible quick connect or similar that won't propogate the resonance through the pipework.

Thanks for your input, you have just made me realise that I can easily (temporarily) remove the backflow value and see if the noise goes away. Will give that a try on the weekend.

I have just had a closer look at my backflow valve and it does look as though it will come apart. It looks like the end unscrews, probably it is very tight. Interestingly the valve fitted to the front of the house is different, it seems to be the next size larger. I suspect I got whatever the plumber had left, he was very disorganised. I had to give him some sandpaper to clean the copper pipe and he used a couple of my left over fittings as he had run out....

Post a picture of your valves. They should be RPZDs if you're also connected to towns water. If so, they must be serviced by someone licensed in backflow prevention.

Here are some photos, the first one is of the backflow valve on the mains water side of the house. The mains supply comes from the left and the house is on the rights. The shut off valve is in the bottom left of the photo.


The next photo is at the back of the house (ie rainwater side). This seems to be the noisy valve. The rain water tank is to the left of picture and the house connection (via a water softener loop) is to the right.

The second one (back/rainwater) is a size smaller than the front one. It is also interesting that despite looking similar they are obviously constructed differently. In both cases water flow is left to right, yet on has the big nut on the left hand end and the other has the big nut on the right.
When my wife doesn't need the water for a while I plan to remove the one at the back of the house, rejoin the pipes, and see if the noise goes away. This unit is the less critical one as it is protecting our rainwater tank from contamination from mains water ). The one at the front of the house is critical as it protects the mains supply from our messy rainwater.

Hmm, they look to be DUAL check valves. I'd check with your local water authority as I suspect the one at the front of the house should be an RPZD, or there should be one installed at the meter. If this is the case you might be able to put it back on the original plumber. You don't want to get caught out unexpectedly with having to rectify this. At the very least it should be a testable device.

Originally Posted by wonderplumb

Hmm, they look to be DUAL check valves. I'd check with your local water authority as I suspect the one at the front of the house should be an RPZD, or there should be one installed at the meter. If this is the case you night be able to put it back on the original plumber. You don't want to get caught out unexpectedly with having to rectify this. At the very least it should be a tastable device.

I have done some more investigation and yes they are both dual check valves. I am in SA and according to SA water's Rainwater Plumbing Guide (found at Overview for plumbers - SA Water ) providding that it is a low hazard install (above ground tank and low litter loads) all that is required is a dual check valve on the mains supply side and on the tank side a single check valve.

I quote the guide
"As a minimum, a backflow prevention device must be installed to protect the mains water supply from the rainwater supply, eg a ‘dual check valve’ located at the property boundary (this device may vary depending on the level of hazard)."
and
"A device such as a single-check non-return valve must be installed on the pipeline from the rainwater tank to prevent uncontrolled mains water from the reticulated supply flowing into the rainwater tank (this check valve may be incorporated within the automatic switching device)"

I assume that the requirements vary between states. It looks like the plumber has met the SA rules, in particular testable devices are not required.

I took the suspect check valve out today, reconnected the pump and there was no noise. So the valve was the problem. I undid the valve (the body is actually a barrel union) and had a look inside. It doesn't look like it is meant to come apart. I will just get a new valve and hop this one doesn't start making a noise. I might have a go at busting the old one apart for a curiosity look...

The conclusion ...

It turns out that the dual check valve that I had can be disassembled. I didn't see any obstruction, but perhaps there was something small. I put it back together and tested it on the back tap. No noise ). I have reinstalled it and so far it is quiet.

Had one minor problem, the valve unscrews and has a fibre washer (like a tap body washer but bigger) between the two halves. While the valve was apart (about a day) this washer dried out and shrunk and wouldn't fit back in. I soaked it in water for a few hours and fortunately it expanded back.