a sump/skimmer physics puzzle

Aquarist007 · 02/29/2008, 10:25 PM

I have read in past posts, as other proactive reefers here, that your skimmer has a level of water in the sump that it requires for maximum effeciency. Alot of guys raise the skimmer body on a brick for eg if they want to keep the level of water higher in the sump.
I have experienced this myself--filling the sump up higher(still keeping the power failure space) affects the intensity of bubbles in the inner column of the Berlin.

Can any one explain the physics behind this concept?

alve · 02/29/2008, 10:35 PM

I responded on your other thread before I saw your link to this one so I copied it here:

Capn, I think the water level in the skimmer can only be at a certain level so once it starts swirling around and get mixed with the air bubbles it would get swirled up too high causing it to overflow in the skimmer cup. It's like having a glass of water filled to 1/2" from the top, you can barely swirl it before it goes over the edge of the glass. If you just put an inch of water in that same glass you can swirl it a lot harder before it goes over the edge.
Does this make any sense?

spleify · 03/25/2008, 10:34 PM

Very interesting thread. I can't believe this hasnt got anymore replys.
I agree and noticed something when I was breaking in my new skimmer for a new setup I am in the process of. What you said alve, makes sence. It should have something to do with back pressure, I would assume.

Spleify

connpatd · 03/26/2008, 03:47 PM

I thought it had to do with it taking more effort, when the water level is high, to suck air down the hose to the pump while at the same time the water enters the pump easier, thus at a particular setting, raising the water level would cause more water and less air to enter the skimmer....thus less bubbles and the potential to overfill the skimmate cup with water.

Is this wrong?

Jefe12234 · 03/26/2008, 03:48 PM

I think this stems from the fact that the venturi has to pull air down from the surface (through the tubing). If the pump is too deep, then the venturi struggles to pull air down. Personally, I haven't noticed any performance differences when running at differing water levels, but others have so it can make a difference.

Aquarist007 · 03/26/2008, 04:21 PM

Quote:

Originally posted by Jefe12234
I think this stems from the fact that the venturi has to pull air down from the surface (through the tubing). If the pump is too deep, then the venturi struggles to pull air down. Personally, I haven't noticed any performance differences when running at differing water levels, but others have so it can make a difference.

thanks for posting -----I don't know about that however, last summer do to pH problems I had to vent my venturi line outdoor.
It was about 5 feet(3 straight up) and the skimmer pump was still able to get adequate air

at least the post got bumped so maybe someone else will come forward

alve · 03/26/2008, 05:19 PM

I agree with Capn. I believe pulling air doesn't have much to do with it. I am also using about 5 feet of tubing for the venturi and get air sucked in from outside.
My skimmer works exactly the same with or without the 5ft tubing so the venturi doesn't seem to struggle at all with sucking air down.
I use the 5ft tubing for exactly the same reason as Capn, to get outside air and it is doing that year round. Another advantage of that I noticed is that the venturi line does not clog up with salt buildup. Before using the 5ft tubing I had to suck some warm water through the venturi every couple of weeks because it was getting clogged up, I haven't had to do it once since I use the tubing.

Jefe12234 · 03/26/2008, 05:31 PM

I didn't mean the length of the tubing, I meant the distance from the water surface to the pump. It requires more force to pull air deeper underwater. So the venturi pulls less air in deeper water. That's my assumption anyway.

alve · 03/26/2008, 05:37 PM

Correct me if I am seeing this wrong but a venturi line going through 7 inches of water, 12 inches of water or to make it more extreme 3 feet of water, it wouldn't make a difference. The air goes through the venturi tubing without making any contact with the water. The air inside the venturi tubing doesn't meet any more resistance if that tubing is outside the water or in the water.

silverwolf72 · 03/26/2008, 05:59 PM

You need a stronger vacuum to pull the air down the further the line is under water. Try blowing bubbles with air hose at the top of the tank and then try doing the same thing at the bottom of the tank. So your trying to balance the back pressure from the water inside the skimmer and the pressure of water try go up the the venturi.

dzeadow · 03/26/2008, 06:06 PM

alve, ever tried sucking on a garden hose under water? if you were 3' underwater sucking on the hose, it'd be a hell of a lot harder to get air vs. being 6" w/ a snorkel.. just an example. I've tested this several times with pumps when doing venturis. If you put a pump w/ a venturi on it and an air meter at 0 head pressure, it'll suck a certain amount, if you drop it to the bottom of a 5g bucket, it will drastically decrease.. I've had pump completely stop sucking air at the bottom because it didn't have enough power to pull it down the length of airline...too much pressure.

Aquarist007 · 03/26/2008, 06:06 PM

I understand that thanks--but like alve said--we are only talking about raising the height of the water in the sump about 6 inches--that will make that great a difference?

dzeadow · 03/26/2008, 06:09 PM

it'll make a noticeable difference depending on your pump

Aquarist007 · 03/26/2008, 06:12 PM

Quote:

Originally posted by dzeadow
it'll make a noticeable difference depending on your pump

thanks

dzeadow · 03/26/2008, 06:17 PM

just for another example, I have a Sicce psk2500 that should be pulling 35-40scfh w/ the mods I've done to it and it's only pulling 25-30 because it's 10" underwater inside my crappy DIY skimmer, which I'm re-doing, and I'll redo the pump mods and get somewhere between 45-50scfh. It's the difference of skimming a 75g tank and 200g tank (roughly)

alve · 03/26/2008, 09:47 PM

Thanks for the info! I never thought it would make any difference in such small of a distance.

Please explain me this dzeadow:
Let's say a pump pumps 1000g an hour. If you have the pump 6 inches under water or 12 inches under water would that make a difference? I would expect it will still pump 1000g an hour at 12 inches and wouldn't the air being sucked in be related with the amount of flow going through the pump?
The amount of water/air being pulled into the pump is caused by spinning of the propeller. Won't the propeller spin at the same speed at 6 inches and 12inches meaning it is pumping the same?

I understand if you suck air through a garden hose at 3ft deep it will be very hard to do compared with using a snorkel because of the water pressure pushing and making it harder for you to inhale air at a lower pressure than the surrounding water. Would it make a motor spin a propeller slower?

I am definitely not saying you are wrong and am not trying to start a discussion so please don't take this the wrong way. It just got me thinking and I can't figure it out and it is bugging me lol.

sjm817 · 03/26/2008, 10:01 PM

When the skimmer is in deeper water, the pump has more head pressure on it, so it pumps less. This is only true of a non recirculating skimmer.

Aquarist007 · 03/26/2008, 10:03 PM

Quote:

Originally posted by sjm817
When the skimmer is in deeper water, the pump has more head pressure on it, so it pumps less. This is only true of a non recirculating skimmer.

why do you always make things so simple to understand

thanks sjm

drparker · 03/26/2008, 10:06 PM

I go with water pressure at the pump. The first time I put big arm length gloves on reached in the tank I was shocked at much water pressure i could feel and how quickly it increased as I went deeper.

02/29/2008, 10:25 PM	#1
Aquarist007 Registered Member Join Date: Apr 2007 Location: Hamilton, Canada Posts: 28,240 Blog Entries: 1	a sump/skimmer physics puzzle I have read in past posts, as other proactive reefers here, that your skimmer has a level of water in the sump that it requires for maximum effeciency. Alot of guys raise the skimmer body on a brick for eg if they want to keep the level of water higher in the sump. I have experienced this myself--filling the sump up higher(still keeping the power failure space) affects the intensity of bubbles in the inner column of the Berlin. Can any one explain the physics behind this concept? __________________ I prefer my substrates stirred but not shaken Current Tank Info: 150gal long mixed reef, 90gal sump, 60 gal refugium with 200 lbs live rock

03/25/2008, 10:34 PM	#3
spleify Registered Member Join Date: Dec 2003 Location: Denver, Colorado Posts: 9,579	Very interesting thread. I can't believe this hasnt got anymore replys. I agree and noticed something when I was breaking in my new skimmer for a new setup I am in the process of. What you said alve, makes sence. It should have something to do with back pressure, I would assume. Spleify __________________ Make it a Great Day!!!! Current Tank Info: 60 gal SPS cube, with 25 gal refugium, 400W MH, DIY Lumenarc III, DIY skimmer, DIY stand and canopy. 40 breeder LPS with 40 gallon sump, DIY stand, 250W MH

03/26/2008, 03:48 PM	#5
Jefe12234 Registered Member Join Date: Apr 2001 Location: MN Posts: 885	I think this stems from the fact that the venturi has to pull air down from the surface (through the tubing). If the pump is too deep, then the venturi struggles to pull air down. Personally, I haven't noticed any performance differences when running at differing water levels, but others have so it can make a difference. __________________ Serenity now!!!

03/26/2008, 05:31 PM	#8
Jefe12234 Registered Member Join Date: Apr 2001 Location: MN Posts: 885	I didn't mean the length of the tubing, I meant the distance from the water surface to the pump. It requires more force to pull air deeper underwater. So the venturi pulls less air in deeper water. That's my assumption anyway. __________________ Serenity now!!!

03/26/2008, 06:06 PM	#11
dzeadow Premium Member Join Date: Sep 2007 Location: Bozeman, MT Posts: 2,589	alve, ever tried sucking on a garden hose under water? if you were 3' underwater sucking on the hose, it'd be a hell of a lot harder to get air vs. being 6" w/ a snorkel.. just an example. I've tested this several times with pumps when doing venturis. If you put a pump w/ a venturi on it and an air meter at 0 head pressure, it'll suck a certain amount, if you drop it to the bottom of a 5g bucket, it will drastically decrease.. I've had pump completely stop sucking air at the bottom because it didn't have enough power to pull it down the length of airline...too much pressure. __________________ - Danny Current Tank Info: Dual 50 Breeder system, 30g custom sump/fuge, MSX200, Tank1-6x24T5 retro, Tank2-4x39T5 retro

02/29/2008, 10:35 PM	#2
alve Registered Member Join Date: Feb 2002 Location: Redwood City, CA Posts: 312	I responded on your other thread before I saw your link to this one so I copied it here: Capn, I think the water level in the skimmer can only be at a certain level so once it starts swirling around and get mixed with the air bubbles it would get swirled up too high causing it to overflow in the skimmer cup. It's like having a glass of water filled to 1/2" from the top, you can barely swirl it before it goes over the edge of the glass. If you just put an inch of water in that same glass you can swirl it a lot harder before it goes over the edge. Does this make any sense?

03/26/2008, 03:47 PM	#4
connpatd Registered Member Join Date: Aug 2007 Location: Houston, TX Posts: 182	I thought it had to do with it taking more effort, when the water level is high, to suck air down the hose to the pump while at the same time the water enters the pump easier, thus at a particular setting, raising the water level would cause more water and less air to enter the skimmer....thus less bubbles and the potential to overfill the skimmate cup with water. Is this wrong?

03/26/2008, 05:19 PM	#7
alve Registered Member Join Date: Feb 2002 Location: Redwood City, CA Posts: 312	I agree with Capn. I believe pulling air doesn't have much to do with it. I am also using about 5 feet of tubing for the venturi and get air sucked in from outside. My skimmer works exactly the same with or without the 5ft tubing so the venturi doesn't seem to struggle at all with sucking air down. I use the 5ft tubing for exactly the same reason as Capn, to get outside air and it is doing that year round. Another advantage of that I noticed is that the venturi line does not clog up with salt buildup. Before using the 5ft tubing I had to suck some warm water through the venturi every couple of weeks because it was getting clogged up, I haven't had to do it once since I use the tubing.

03/26/2008, 05:37 PM	#9
alve Registered Member Join Date: Feb 2002 Location: Redwood City, CA Posts: 312	Correct me if I am seeing this wrong but a venturi line going through 7 inches of water, 12 inches of water or to make it more extreme 3 feet of water, it wouldn't make a difference. The air goes through the venturi tubing without making any contact with the water. The air inside the venturi tubing doesn't meet any more resistance if that tubing is outside the water or in the water.

03/26/2008, 05:59 PM	#10
silverwolf72 Registered Member Join Date: Jul 2005 Location: Lake Forrest CA Posts: 1,732	You need a stronger vacuum to pull the air down the further the line is under water. Try blowing bubbles with air hose at the top of the tank and then try doing the same thing at the bottom of the tank. So your trying to balance the back pressure from the water inside the skimmer and the pressure of water try go up the the venturi.

03/26/2008, 06:09 PM	#13
dzeadow Premium Member Join Date: Sep 2007 Location: Bozeman, MT Posts: 2,589	it'll make a noticeable difference depending on your pump __________________ - Danny Current Tank Info: Dual 50 Breeder system, 30g custom sump/fuge, MSX200, Tank1-6x24T5 retro, Tank2-4x39T5 retro

03/26/2008, 06:17 PM	#15
dzeadow Premium Member Join Date: Sep 2007 Location: Bozeman, MT Posts: 2,589	just for another example, I have a Sicce psk2500 that should be pulling 35-40scfh w/ the mods I've done to it and it's only pulling 25-30 because it's 10" underwater inside my crappy DIY skimmer, which I'm re-doing, and I'll redo the pump mods and get somewhere between 45-50scfh. It's the difference of skimming a 75g tank and 200g tank (roughly) __________________ - Danny Current Tank Info: Dual 50 Breeder system, 30g custom sump/fuge, MSX200, Tank1-6x24T5 retro, Tank2-4x39T5 retro

03/26/2008, 09:47 PM	#16
alve Registered Member Join Date: Feb 2002 Location: Redwood City, CA Posts: 312	Thanks for the info! I never thought it would make any difference in such small of a distance. Please explain me this dzeadow: Let's say a pump pumps 1000g an hour. If you have the pump 6 inches under water or 12 inches under water would that make a difference? I would expect it will still pump 1000g an hour at 12 inches and wouldn't the air being sucked in be related with the amount of flow going through the pump? The amount of water/air being pulled into the pump is caused by spinning of the propeller. Won't the propeller spin at the same speed at 6 inches and 12inches meaning it is pumping the same? I understand if you suck air through a garden hose at 3ft deep it will be very hard to do compared with using a snorkel because of the water pressure pushing and making it harder for you to inhale air at a lower pressure than the surrounding water. Would it make a motor spin a propeller slower? I am definitely not saying you are wrong and am not trying to start a discussion so please don't take this the wrong way. It just got me thinking and I can't figure it out and it is bugging me lol.

03/26/2008, 10:01 PM	#17
sjm817 On Yer left! Join Date: Sep 2004 Location: Northern VA Posts: 18,777	When the skimmer is in deeper water, the pump has more head pressure on it, so it pumps less. This is only true of a non recirculating skimmer. __________________ - Scott

03/26/2008, 10:06 PM	#19
drparker Registered Member Join Date: Feb 2006 Location: Palatine, IL Posts: 2,652	I go with water pressure at the pump. The first time I put big arm length gloves on reached in the tank I was shocked at much water pressure i could feel and how quickly it increased as I went deeper.