Jobo 2553 tank with volume-saving spacer?

[Kawaiithulhu]

I've got a Jobo 2553 tank that has a plastic donut spacer that fits around the shaft to save on chemistry volume, it looks to take up a little less space than a reel set for 120 film. I can't find any documents on how much, or even the part referenced or part number (04 077) showing at the main web site.

Does anyone know offhand how much from the 640ml/560ml volume is reduced?

It'll save me from having to try some wacky antics getting a proper measurement without the lid on.

 

[darkroommike]

Wacky as in put the donut in the tank, fill the tank with water, pour out water into a graduate and then repeat without the donut? The donut may not be a JOBO part, they were commonly used in Phototherm and King Concept processors.

 

[grahamp]

It's a bit more complicated if the tank is rolled, as the solution volume is a little under half the volume of the tank, down to the minimum required to develop the film. The simplest approach might be to fill the tank, then lay it on it's side level in a tray or sink to drain the excess water, then measure the remaining volume. Repeat with the 'doughnut' in place. That will give you the maximum effective volume difference. The ratio of the two should give you the ability to get the difference for minimum chemistry. This assumes that the 'doughnut' is almost the diameter of the tank. If it is significantly smaller then volume ratio is going to be off (you would need more than the calculated amount). As long as you are using more than the minimum chemistry you should be safe.

The other way is to measure everything and calculate the actual volumes when it is on it's side. Area from a chord of a circle (circular segment in Wikipedia) is not too hard to calculate, and it has to be extrapolated to effective volume.

Who said you would never find a use for mathematics and geometry after school?

 

[Kawaiithulhu]

Except that the plastic donut has a Jobo standard part number, I did find one internet mention of it last night in an ATL-1000 sale that's years old.

I was hoping someone knew or had an old system manual, and I've got a note off to Jobo support, before having to get wet with the empirical testing.

Easier test: half fill a large graduated cylinder, measure, force down the donut, measure again. The displacement is the volume change. None of this repeated pours. Bonus if I yell out "Eureka!" at the end!