Venturi vs Needle wheel

MarlinHooker · 12/01/2008, 07:49 PM

Ok, I think I finally settled on the skimmer for my new 150, a ProClear Impact 200. The folks at my LFS use ProClear skimmers on all their systems and they took me in the back and showed them operating.

There is also a very positive review about them here: http://www.nano-reef.com/forums/inde...owtopic=159923

While reading up on them they said they are the venturi type skimmer and most propaganda I read these days talks about needle wheel skimmers.

So what's the difference and is one really 'better' than the other?

hairyman1 · 12/09/2008, 12:55 AM

Looks similar to bermudas design, but the picture I saw I couldn't make out any discharge adjustment to raise or lower the water level inside the skimmer. That is very convenient to have. Do these skimmers come with a pump? Venturi skimmers pump water through a small oriface similar to an hourglass (it does vary somewhat) with the air input in the middle where the oriface is narrowest. This creates negative pressure as water is pumped through it drawing in air which mixes with the water. The more powerful the pump the more air injected (to a point). Aspirating needle/pin/mesh wheel skimmers have the air inlet before the pump also through a reduced inlet pipe that is simpler in design which also creates negative pressure, but does not require a powerful pump to operate. The specialized impeller shreds the injected air into the very finest bubbles which in some designs resemble shaving cream. Aspirating skimmers are more electrically efficient and lower priced pumps can be used as long as they have a large enough volute cover to mix the air that is drawn in. Venturi skimmers rely on pump pressure and volume in addition to venturi size to make fine bubbles. The bubbles are not as fine as the needle wheel skimmers so they have less surface area and theoretically should not be as efficient, but because the volume of dirty water is higher the better designs appear to make up for that and produce similar quantities of skimmate with a higher electrical cost. IMO recirculating is the way to go with any design as it corrects water level fluctuations that annoy reefers. The high tech venturis today are becketts and mazzei which from the ones I've seen can produce a very fine bubble and lots of them along with lots of flow. Remember skimmer function is about air/water mixing not just adding more air while sacrificing flow. That's a no no for long term performance which is another good reason for a recirculating design as you can have a specialized pump to mix large quantities of air at a slow/moderate flow rate and pick your process flow rate pump for the process water which gives you more control over how much water you can skim per hour. Another issue is consistancy of skimmate and maintenance. This is where the better venturi designs pull a little ahead the the routine maintenance is of a lower frequency then needlewheels in general and they are less disturbed by weather changes. Not much discussed, but easily demonstrated are skimmer foam head expanding and contracting with barometric changes which results in erratic skimmer performance. This is easily tested by placing a barometer in the room with a needlewheel skimmer and keeping notes on performance during different barometer readings. Needlewheel designs seem to fluctuate more and I have no idea why except that it might have something to do with creating negative pressure before or after the skimmer pump. All skimmers react to changes in barometric pressure by the way. Also because better needlewheel designs and becketts draw in more air the foam head may contract more due to local inside air pollution such as cooking smoke and airborn sprays. Again one has to keep notes to be aware of this and to see when patterns develop. I haven't talked about skimmate color as it's more manipulated by bioload/additives in your tank and less on skimmer design. There's so much more we don't yet know, But there are many more needlewheel types being produced/copied today than venturis so you can go with the flow or walk your own path just pick a good solid design and have some skimmate on me.

12/01/2008, 07:49 PM	#1
MarlinHooker Registered Member Join Date: Nov 2008 Location: Indialantic, FL Posts: 690	Venturi vs Needle wheel Ok, I think I finally settled on the skimmer for my new 150, a ProClear Impact 200. The folks at my LFS use ProClear skimmers on all their systems and they took me in the back and showed them operating. There is also a very positive review about them here: http://www.nano-reef.com/forums/inde...owtopic=159923 While reading up on them they said they are the venturi type skimmer and most propaganda I read these days talks about needle wheel skimmers. So what's the difference and is one really 'better' than the other?

12/09/2008, 12:55 AM	#2
hairyman1 Registered Member Join Date: Oct 2007 Location: Illinois Posts: 271	Looks similar to bermudas design, but the picture I saw I couldn't make out any discharge adjustment to raise or lower the water level inside the skimmer. That is very convenient to have. Do these skimmers come with a pump? Venturi skimmers pump water through a small oriface similar to an hourglass (it does vary somewhat) with the air input in the middle where the oriface is narrowest. This creates negative pressure as water is pumped through it drawing in air which mixes with the water. The more powerful the pump the more air injected (to a point). Aspirating needle/pin/mesh wheel skimmers have the air inlet before the pump also through a reduced inlet pipe that is simpler in design which also creates negative pressure, but does not require a powerful pump to operate. The specialized impeller shreds the injected air into the very finest bubbles which in some designs resemble shaving cream. Aspirating skimmers are more electrically efficient and lower priced pumps can be used as long as they have a large enough volute cover to mix the air that is drawn in. Venturi skimmers rely on pump pressure and volume in addition to venturi size to make fine bubbles. The bubbles are not as fine as the needle wheel skimmers so they have less surface area and theoretically should not be as efficient, but because the volume of dirty water is higher the better designs appear to make up for that and produce similar quantities of skimmate with a higher electrical cost. IMO recirculating is the way to go with any design as it corrects water level fluctuations that annoy reefers. The high tech venturis today are becketts and mazzei which from the ones I've seen can produce a very fine bubble and lots of them along with lots of flow. Remember skimmer function is about air/water mixing not just adding more air while sacrificing flow. That's a no no for long term performance which is another good reason for a recirculating design as you can have a specialized pump to mix large quantities of air at a slow/moderate flow rate and pick your process flow rate pump for the process water which gives you more control over how much water you can skim per hour. Another issue is consistancy of skimmate and maintenance. This is where the better venturi designs pull a little ahead the the routine maintenance is of a lower frequency then needlewheels in general and they are less disturbed by weather changes. Not much discussed, but easily demonstrated are skimmer foam head expanding and contracting with barometric changes which results in erratic skimmer performance. This is easily tested by placing a barometer in the room with a needlewheel skimmer and keeping notes on performance during different barometer readings. Needlewheel designs seem to fluctuate more and I have no idea why except that it might have something to do with creating negative pressure before or after the skimmer pump. All skimmers react to changes in barometric pressure by the way. Also because better needlewheel designs and becketts draw in more air the foam head may contract more due to local inside air pollution such as cooking smoke and airborn sprays. Again one has to keep notes to be aware of this and to see when patterns develop. I haven't talked about skimmate color as it's more manipulated by bioload/additives in your tank and less on skimmer design. There's so much more we don't yet know, But there are many more needlewheel types being produced/copied today than venturis so you can go with the flow or walk your own path just pick a good solid design and have some skimmate on me.