Flow switch for UV filter

[Steve604]

My UV filter is currently on 24/7 and acts like a little hot water tank on the cold water line when there is no water flow for a few hours. I was thinking about putting in a flow switch that will turn it on and off. Is there any reason not to?

I also have a Rainfresh automatic backflushing iron filter that measures water flow. I am trying to figure out if I can tap into the internal curcuitry to power a relay that would control the UV filter. Does anyone have any electrical specs/diagrams for the head unit in the pics attached? I see 2 pins in a yellow plug on the circuit board that I'm hoping might be an external dry contact for water flow.

 

[Jeremy Harris]

I asked this very question of a UV steriliser supplier around a year ago, for exactly the same reason. I was given two reasons as to why you shouldn't do this, neither of which I'm 100% sure are true. The first was that the UV tube takes a few seconds to warm up, so water could pass though without having been adequately irradiated. We'll, I checked mine and it looks like it fires up straight away, so I'm not sure I wasn't being spun a line.

The second reason was that switching the tube on and off would shorten it's life. This seemed to have some basis in fact, but when I did a bit of digging around it seemed to originate from the time when these tubes used electromechanical starters, like a florescent lamp. It looks like it may not be true for newer units that use an electronic starter and control box.

The bottom line is that these tubes are identical in the way they operate to a florescent tube light, in fact that's all they are but without the layer of phosphor on the inside that turns the UV light into white light, as I under stand them. As such they should be OK to be turned on and off in the same way as a florescent tube, and if frequent switching does shorten their life a bit, then maybe have a flow switch with a timer, to avoid short cycling the thing.

I have a feeling that the extended tube life from being off a lot of the time, plus the reduced electricity use, could end up making it a cheaper way to run these things. However, the manufacturers want you to buy a new tube every year, so my guess is that they aren't going to be enthusiastic about something that cuts their tube sales!

 

[Sponsor]

 

[Valveman]

If you only want the light to come on when there is water flow, you could tie the power for the light into the pump side of the pressure switch.

 

[DonL]

" The first was that the UV tube takes a few seconds to warm up, so water could pass though without having been adequately irradiated."

The fact that it looks like it is operating at max output, Does not mean that it is.

If you take a measurement, Some tubes may reach peak and proper output frequency around 1 Minute.

It is a Tube.

 

[Jeremy Harris]

Good points. I may be able to borrow a UV light meter from my former employer, as they used the same lights to sterilise glove boxes, so with one of those and one of my spare tubes I may be able to answer the question once and for all. It'd be nice to only have sterilisation when needed, rather than have the tube burning away its life 24/7. Better still would be for UV LEDs to be developed to the point where they are suitable and affordable for this job, as that would open up loads of opportunities , like sterilisation right at the point of use, as well as sterilisation on the main feed.

Maybe I'm a bit paranoid but one thing that bothers me with UV sterilisation is that there is no lingering anti-bacterial effect as there is when using chlorine (or bromine). I've noticed how the water in the house will smell a bit musty after we've been away for a few days, and the systems needs to be flushed through for a few minutes to get back to sweet smelling water again, which I guess is down to stuff growing in the pipes when the house is shut up for a while. Probably not harmful (we probably worry too much about bugs anyway), but a small UV LED steriliser at each outlet, operated by a flow switch, seems like a neat idea, once the technology is mature enough.

 

[Steve604]

I think I'm going to just go ahead and do it. I'm not too worried about bacteria here, the UV filter is just precautionary.

I have a constant presure system and I'm currently using the aux output contact on the controller for my air injection system. I suppose I could just run the UV light off the same relay or run the UV light off of that contact and the air injection off of an inline flow switch.

The only other annoyance will be the beep from the ballast of the UV filter every time it turns on.

Now that I think about this some more, doing this may shorten the life of the ballast. This still might be worth it over the long term with power savings.

 

[Craigpump]

Just how much do you think you'll save?

Do you unplug your modem, cable box and TV when they aren't being used?

 

[Steve604]

I won't save much if anything but at least I'll get rid of that mini hot water tank on my cold water line

 

[Gardner]

Even when the water is not flowing through the U/V sterilizer, there is a continuous column of water for the bacteria to move around in. Giardia and cryptosporidium actually actively swim. Bacteria will move around by diffusion. This can put live baddies on the clean side of the sterilizer when the water starts to flow again.