View Full Version : Why are Air Pumps rated 'Up to'?
Rocketman
12-13-2002, 5:54 PM
Hey. I am purchasing a Rena Air Pump and trying to decide whether I should go with the #200 ($25.99) or #300 ($36.99) model. The #200 pump says, 'up to 30 US Gallons,' and the #300 says, 'Up to 75 US Gallons.' Being as this is a 60 Gallon tank, the logical choice would be the #300. But since the air pump is not pumping water, I was wondering why there is any capacity rating. If the #200 puts out less air, this would be a plus as this will be a mildly planted tank.
Any thoughts? Also, if you have heard any bad things about these brands, speak up please. Also, those prices are from Bigals.
Shiftaltumlock
12-13-2002, 6:07 PM
Interesting question!!
I would guess that the ratings are based on how much air it takes to drive UGF's of varing sizes. It seems like a very "hit & Miss" formula.
So basically, if you are driving 4 uplift tubes, you want the bigger pump. If driving 2, the smaller would do.
Geez!!! It has been along time since I have messed with uplift tubes. It seems like a lifetime ago.
Rocketman
12-13-2002, 6:11 PM
Hey, thanks for the reply. No UGF system, just pumping free air through an air stone for aeration. But from your reply, I assume the #200 will do. It saves me like $9 so its worth it.
Shiftaltumlock
12-13-2002, 7:35 PM
Heaters:
The reason for 2 smaller heaters vs. 1 large heater is for redundency. If one heater goes out(not heating) the other can take up the slack until the broken one is replaced. Also, If a large heater sticks in the "ON" position. Your tank will heat up much more and much faster than if one of the smaller heaters sticks in the "ON" position. The Ebo-Jager is the best choice IMO. If you choose to have only one heater, this is the brand to go with. It is a very tough and reliable unit. (It looks slick too)
Gang Valve:
Penn Plax makes a decent one. I have used the 3way and 5way valves from them and never had a problem. I did notice that the valves are not very sensitive. I would prefer a bit more control than what that unit gave me.
Filter Media:
Ehfisubstrat is the Bio-media provided with Eheim canisters. You want this for sure. I did not use all the media that came with my 2028 because I have a planted tank. Chemical fitering tends to remove fertilizers. I did use the Ehfisubstrat, the foam pads(not carbon ones) and the EHFI-Mech ceramic rings.
That is one great filter. You will love it.
Rocketman
12-13-2002, 9:28 PM
One last thing. Do the pipes to direct the water flow come with the filter? I assume the hoses do, anything else I need
i'm confused at a few of the answers posted.....
the answer to your basic question tho, is the pumps are rated for a reason that hasn't been mentioned yet. pressure. it takes more pressure from the basic pump to drive the air further down a small restrictive tube, especially when you submerge it. the bigger the pump and higher rating, the more tubing and deeper into the water it is expected to have to deal with, so it requires more pressure.
if you bought say the smallest pump, and put it in deep water, even with a small airstone you might not like the results.
good luck
Darkangel
12-14-2002, 2:00 PM
That was my first thought as well ewok. Then I realized that a 35 gallon and a 65 gallon tank are both the same depth namely 18 inches. Having said that I would have thought it would be far more helpful if the pumps were rated for their number of outputs and depth to which it is suitable for. That information would make for better then ranking because of tank size.
Rocketman
12-14-2002, 2:14 PM
Thats just what I thought too! It must be PSI or something like that, but consider this. If you place an air line at the bottom of a 35 gallon tank that is say, 18 inches tall, there is still less pressure pushing at it from the sides then there would be if it were placed at the bottom of a 100 gallon tank which was also 18 inches tall. Now, granted those towo measurments aren't likely, but its the princible that matters. But, would a #200 work? Like I said, I would prefer a low output as I want this tank as quiet as possible, and it will be planted.
Darkangel
12-14-2002, 3:24 PM
Pressure would only matter in the downward direction. You would have the same preasure in a vessel 5 inches across or five feet across so long as the depth is the same and they are at the same feet above sea level. PSI is a measurement in this case of resistance and it would matter little how much water we are talking but only how deep the water is.
sort of vaguely disagree on theory or principle darkangel..... if that was the case then my 55 and 90 should be made of the same thickness glass.... maybe i'm overtired, but water pressure is water pressure, it's not measured just by depth, i think weight has to figure into this too..............
Darkangel
12-15-2002, 10:00 AM
Is the 55 not 18 high and the 90 twenty four inches high ewok? You are also talking about the preasure being applied to a much larger area. In the airstone case the preasure is applied to a very small space and is the same in any size tank I think. I am not 100% sure here and I may be wrong but water preasure is as you say a function of weight which is in itself a function of gravity which is a downward preasure. Perhaps someone with more knowledge in science and such could pipe in and set things straight.
that was basically just a "for instance" darkangel, i know i am treading on iffy ground myself. and the 90 could be filled to the same height as the 55............
just for the sake of arguement..... i don't believe all pressure is equal tho....... but scientifically i am unable to do it atm.
carpguy
12-15-2002, 3:02 PM
The bubbles don't care how heavy the water in the tank is. The weight of the water above them is their only constraint. If you have an 18" cube the bubbles have 18" of water on top of them. If you extend the walls so that you have a 48x18x18 tank the pressure on the bubbles remains the same, the weight of the water, and the outward pressure on the sides, changes. The surface area of the bubbles is the same in both scenarios, the surface area of the tank is not.
Faramir
12-16-2002, 6:22 AM
Darkangel is correct - water pressure in PSI is purely a function of depth. Otherwise just think how terrible the pressure would be 18" down in the sea!
Larger tanks need thicker glass because each piece of glass is longer, and therefore more strength is needed to prevent it from bowing and breaking. Imagine you have a twig 12" long. If you support it at each end, you can easily break it by hitting it in the middle. If you put two supports under it only 2" apart, far more pressure is required to break the twig.
Bracing is also used for strengthing, of course.
It's easy enough to demonstrate, if you don't believe me! Take a large container, such as a large ice cream tub, fill it with water to 4" say, make a hole in the side at the bottom and observe how far the water comes out horizontally as it falls. Then do the same with a washing up liquid bottle with the same depth of water in it. You will find the water emerges with the same force, as long as you make the same size hole.
This site: http://theory.uwinnipeg.ca/physics/fluids/node8.html explains the physics; I draw attention to the sentence: "Note: Only the density of the fluid and the difference in depth affects the pressure. The shape and size of the container are irrelevant. Thus the water pressure 6 inches below the surface of the ocean is the same as it is 6 inches below the the surface of a glass of salt water. "