Date:         Wed, 29 Jan 1997 08:38:00 -0500 Reply-To:     MARTIN TAI <martin.tai@w....> Sender:       The Subminiature Photography Mailing List               <SUBMINI-L@LISTSERV.AOL.COM> From:         MARTIN TAI <martin.tai@W....> Organization: Westonia Computer Systems of Canada Subject:      Agitation Principles of the Minox Tank                 How "Thermometer Pumping" works in Minox Developing Tank             When  I  got the Minox daylight development tank, I read the instruction in the box,  about insert a thermometer in the center part of the tank, and by moving it up and down to agitate the developer.          For some times, I has being doubtful about this "thermometer pump", wondering how can such mild action serves to agitate the liquid.            As my first tank has a leak in the center, so the thermometer pump did not work.          Now I got a replacement tank, I took a closer look at the construction of the Minox tank, try to answer my own question: "Does the thermometer pumping really works ?"           I was wrong ! The thermometer pump indeed works, thus further my amazement at the  ingenuity of its designer- Walter Zapp.           The following is a cross section of the Minox daylight development tank         T -- the thermometer well       C -  the coil holding the film         When the  coil is put into the tank, it divides  the liquid container into two concentric cylinder partitions, one outside of  the coil, denoted by  'O', the other inside the coil denoted by  'i'        The clearance of  the  'O' partition is 7.2mm      The clearance of  the  'i' partition is 2.3mm        Which are derived by the following measurement with a caliper.                Inner diameter of tank : 46mm              Outer diameter of coil : 38.8mm              'O'      clearance:    : 7.2mm                Inner diameter of coil   : 35mm            diameter  of core        : 32.7mm (at film grove)            [i]    clearance:       : 2.3mm             ( diameter of thermometer hole: 8.0mm )                     C                     C          ||   ||                    ||   ||          ||   ||          T         ||   ||          || O ||  i              i  || O ||         ||   ||    // \\   //\\    ||   ||          ||   ||   ||   ||  || ||   ||   ||          ||   ||   ||   ||  || ||   ||   ||          ||   ||   ||   ||  || ||   ||   ||          ||   ||   ||   ||  || ||   ||   ||          ||   ||   ||   ||  || ||   ||   ||          ||   ||   ||   ||  || ||   ||   ||          ||   ||   ||    \\//  ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||   ||   ||          ||        ||          ||   ||   ||          ||        ||          ||        ||          ||========||          ||========||            Because of the two partitions are separated by a coil, liquid cannot flow freely from the inner partition to the outer partition or visa versa in a horizontal manner.          Instead, liquid is forced to flow down the narrow inner partition, to the bottom of the tank, than flows to the bottom part of the  outside partition, then up.        There are two triangular shape cut out at the bottom of the core, plus a 3.4mm round hole at the bottom of the film grove to facilitate the flow of between to two partition; all these three 'deep channels' are at or near the bottom of the tank.          The following diagram illustrate pouring  developer into the  center of the tank (T)           1) The developer fills up the 'thermometer well"         2) liquid overflow the  thermometer well, then flow DOWN the inner partition, to the bottom of the tank, passing through the three "deep channels at the bottom of the oil, then flows back UP  along the outer partition.         3) Until the liquid is at same level           Pouring developer                        *                       *                         *                          *                          *          ||   ||         *          ||   ||          ||   || * * * * * * * * *  ||   ||          ||   || * * * * * * * *  * ||   ||          ||   || *  // \\ * //\\  * ||   ||          ||   || * ||   ||* || || * ||   ||          ||   || * ||   ||* || || * ||   ||          ||   || * ||   ||* || || * ||   ||          ||   || * ||   ||* || || * ||   ||          ||   || * ||   ||* || || * ||   ||          ||   || * ||   ||* || || * ||   ||          ||   || * ||    \\//  || * ||   ||          ||   || * ||          || * ||   ||          ||   || * ||          || * ||   ||          ||   || * ||          || * ||   ||          ||   || * ||          || * ||   ||          ||   || * ||          || * ||   ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || *    * ||          || * || * ||          || * * ** ||          || * *  * ||          ||========||          ||========||          Developer filled.                ||   ||                    ||   ||          || * || * * * * * * * * *  || * ||          || * || * * * * * * * *  * || * ||          || * || *  // \\ * //\\  * || * ||          || * || * ||   ||* || || * || * ||          || * || * ||   ||* || || * || * ||          || * || * ||   ||* || || * || * ||         || * || * ||   ||* || || * || * ||          || * || * ||   ||* || || * || * ||          || * || * ||   ||* || || * || * ||          || * || * ||    \\//  || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || * || * ||          || *    * ||          || * || * ||          || * * ** ||          || * * ** ||          ||========||          ||========||     PUSH IN thermometer RAISES the fluid level of inner partition forcing fluid to flow down the INNER partition to to bottom of tank then flow backup through OUTSIDE partition.                                      T                            T          ||   || * * * * * T *  * *  ||   ||          || * || * * * * * T *  * *  || * ||          || * || * * * * * T *  *  * || * ||          || * || *  // \\  T //\\  * || * ||          || * || * ||   || T || || * || * ||          || * || * ||   || T || || * || * ||          || * || * ||   || T || || * || * ||          || * || * ||   || T || || * || * ||          || * || * ||   || T || || * || * ||          || * || * ||   || T || || * || * ||          || * || * ||    \\ //  || * || * ||          || * || * ||           || * || * ||          || * || * ||           || * || * ||          || * || * ||           || * || * ||          || * || * ||           || * || * ||          || * || * ||           || * || * ||          || * || * ||           || * || * ||          || * || * ||           || * || * ||          || * || * ||           || * || * ||          || *    * ||           || * || * ||          || * * ** ||           || * * ** ||          ||========||           ||========||     PULL OUT  thermometer lower the fluid level of inner partition forcing fluid to flow down the OUTER partition to to bottom of tank then flow backup through inner partition.         Thus  pushing down the thermometer, causes the developer to flow up along the film groves, and pull up the thermometer, causes the developer  to flow down along the film grove.     CONCLUSION:         In spite of the seemingly minimum movement of the thermometer, it actually provide effective agitation for developer.       From here we can see Walter Zapp's ingenuity in the design of the Minox daylight development tank.