DI tank 20x2.5 vs 20x4.5

Waterfed Poles
1

I need to add a new DI tank to one of my vehicles and it needs to be smaller than a 1/2 cubic foot for space reasons. This will be used after an RO membrane. I know some will recommend I just buy something ready to go but first I want to compare two sizes of DIY tanks…a 20x2.5 inch and a 20x4.5 inch (big blue), both with refillable cartridge inserts. I know the obvious advantages and disadvantages (mainly initial cost, size, weight, and frequency of changing resin differ between the two). I have two specific questions…

  1. Is there going to be a flow rate difference?
  2. Does anyone know the exact amount of resin that fits in each respective tank? I’ve seen a range of 24 to 32 oz for the smaller tank and 6.5 to 7 lbs for the larger, but would like verification.
2

I have both.
question 1- no difference in flow
question 2- since resin is sold by volume, not weight, just do the math to calculate total cubic inches each chamber holds

3

Yes, just take your height of 20" times Pi times R(square) where Pi is 3.14 and R is the radius of your cylinder. This will give you the volume in cubic inches. To get cubic foot, divide this by 12 three times.

4

Not always. A lot of times smaller quantities are sold by weight, like 5 lb bags. I’m interested to know what the approximate density of DI resin is.

@PressurePoint- if you’ve got the room for it, I would go with the larger vessel. You’ll just save time in not needing to change resin as often.

5

I bought 1 cubic foot of mixed DI resin from WCR before and it weighs 46 lbs.

6

that means there is roughly 736 oz in a cubic foot of resin.
there are 1728 cubic inches in a cubic foot.
that means a cubic inch of resin weights .43 oz.
a 4’x20" cartridge will hold 251 cubic inches, or roughly 108 oz. of resin.
a 2.5"x20" cartridge will hold 98 cubic inches, or roughly 42 oz of resin.

^ is my math right? :confused:

7

Everything seems right except the last calculation. I have Pi(3.14)*square(1.25)*20=98 cubic inches, not 192 cubic inches. Or roughly 42 oz of resin.

It seems like maybe you used R=1.75 but R should be 2.5/2=1.25 instead.

8

^correct! entered the wrong value for R on the 2.5" chamber. thanks.