Gap size between UV bulb and quartz sleeve

[FortuneFavours]

Hi all

I've been doing some cursory reading into UV sterilisation and I've read that, in addition to flow rate / wattage / contact time, a very important consideration is the size of the space between the the UV bulb and the quartz sleeve.

From what I understand, pond UV's have a larger gap (as they're used as water clarifiers, not sterilizers) but for true sterilisation for a marine tank the gap should be as small as possible.

Just wondering if anyone has any knowledge on how small this gap should actually be?

Thanks

 

[zachfishman]

I didn't think this was variable/adjustable. One model, one sleeve, one bulb. What I do see in UV sterilizer manuals are different flow rates for water clarification vs "sterilization" (targeting protozoa and multicellular orgs vs unicellular algae).

 

[FortuneFavours]

I didn't think this was variable/adjustable. One model, one sleeve, one bulb. What I do see in UV sterilizer manuals are different flow rates for water clarification vs "sterilization" (targeting protozoa and multicellular orgs vs unicellular algae).

As a complete novice on the matter, I found this article on UV sterilisation really useful.

It states:
"The design of the unit should only allow a gap of .3 mm or less between the bulb or quartz sleeve and the wall of the unit for effective contact and temperature.

This is where Aquarium Canister UVs, 'Hang-On Back' UV Filters, Most Submersible/Internal UVs, and Pressurized Pond Filters (such as the Aquael, Nursery Pro, even the newer Via Aqua) fail miserably as there is too large a gap, and in general a poor flow design around the bulb/quartz sleeve (as well as flow rates far exceeding UVC bulb wattage capabilities)"

I think he meant 0.3cm (i.e. 3mm)?!

The article mentions TMC as being one of the better options in the author's experience, so I started looking into the TMC P2 (2 x 55W) for my 300G tank.

Curious about the "gap" that this product has, I emailed TMC earlier and have just received a reply (they're very good!):

"The P2 110w UV Steriliser is a true steriliser that will give you 99% control of most single celled organisms on a single pass at a flow rate of 4000LPH. To achieve this you need to keep the water being treated tight to the UV lamp, so this unit has a maximum distance of 12mm from the quartz sleeve.

The Pro Pond Advantage UV110 is a Clarifier designed to control green water in Koi ponds. It takes a much higher flow rate up to a maximum of 36000 LPH, to achieve this sort of flow rate the bore of the unit is larger and has a maximum distance of 25mm from the quartz sleeve. A higher flow rate and larger bore reduces the sterilising effect but is sufficient for the control of green water."

 

[laga77]

The reason the gap should be small is, the intensity of the light decreases the further away from the source you get. Law of inverse squares IIRC. So the closer the water, the stronger the effect. I just purchased a Aqua Ultraviolet unit and the gap is about 1/16 inch. BTW, I did a lot of research before buying this unit and I learned a few things about the UV bulbs in the pond clarifiers. I bought a 55W clarifier off of Amazon on an impulse so I learned the hard way. All the Chinese manufacturers get their bulbs from the same source. These bulbs are rated in µW/cm2. The bulbs from Ultra and Emperor are rated in mJ/cm2. 1 mJ/cm2 = 1000 μW-sec/cm2. So the clarifiers are 1/1000 as strong. IIRC.

 

[FortuneFavours]

I didn't think this was variable/adjustable. One model, one sleeve, one bulb..

Sorry, I meant there were variances between models, not that the distance would be adjustable for a single model.

 

[FortuneFavours]

The reason the gap should be small is, the intensity of the light decreases the further away from the source you get. Law of inverse squares IIRC. So the closer the water, the stronger the effect. I just purchased a Aqua Ultraviolet unit and the gap is about 1/16 inch. BTW, I did a lot of research before buying this unit and I learned a few things about the UV bulbs in the pond clarifiers. I bought a 55W clarifier off of Amazon on an impulse so I learned the hard way. All the Chinese manufacturers get their bulbs from the same source. These bulbs are rated in µW/cm2. The bulbs from Ultra and Emperor are rated in mJ/cm2. 1 mJ/cm2 = 1000 μW-sec/cm2. So the clarifiers are 1/1000 as strong. IIRC.

I remember reading somewhere or other that UV absorption is higher in saltwater than freshwater, so it's even more important to have the light source closer to the water(?)

I'm British, so I had to do a calculation to figure out what 1/16 inch is in mm!! :spin2: Rounding up, that's only 2mm which is pretty awesome, especially if you take into consideration TMC's response.

When you did your research, did you by any chance manage you find out how powerful (not sure if that's the right term) a bulb would need to be (in mJ/cm2 or μW-sec/cm2) in order to effectively kill the nasties we're trying to deal with in the hobby, or is it just a case of "get the best one you can"?

 

[FortuneFavours]

Just thinking about this a bit more and wondering if the following thought process makes any sense?

- The quartz sleeve is there to ensure the water does not touch the bulb and thus reduce the operating temperature (and thus efficiency) of the UV bulb

- There will be another gap between the quartz sleeve and the inside of the housing itself (the area where the water actually flows)

- Therefore the the gap between the UV bulb and quartz sleeve isn't what is most important; what is important is the gap between the bulb and the housing. For example, a steriliser with with a housing chamber that is 60mm in diameter will be more effective at sterilisation than one with a diameter of 100mm (assuming both sterilisers are using the same bulbs and both have a 12mm gap between the bulb and quartz sleeve)

 

[laga77]

Yes the size of the water chamber is important. The unit I just purchased is a 25W and the OD is 2.25-2.5 inches and the sleeve on the inside is around an inch, so the water is only about an inch thick. The bigger the bulbs, the longer they get so the size of the chamber stays the same. I think this only changes in the stronger commercial series. To kill the ICH protozoa you would need 90,000μW-sec/cm2. To achieve this with a 25W bulb, the flow rate needs to be 400 gallons per hour. Check out Aqua Ultraviolet web site and you will find sizing charts for the different power bulbs.

 

[FortuneFavours]

Yes the size of the water chamber is important. The unit I just purchased is a 25W and the OD is 2.25-2.5 inches and the sleeve on the inside is around an inch, so the water is only about an inch thick. The bigger the bulbs, the longer they get so the size of the chamber stays the same. I think this only changes in the stronger commercial series. To kill the ICH protozoa you would need 90,000μW-sec/cm2. To achieve this with a 25W bulb, the flow rate needs to be 400 gallons per hour. Check out Aqua Ultraviolet web site and you will find sizing charts for the different power bulbs.

Great stuff - thank you! :thumbsup: