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This is beautiful! Great for dosing small amounts and most important of all doesn't need to be refilled as often as the Eheim liquidoser seeing you can feed it from any size container. Further it should be able to provide plenty of head so it can all be hidden under the tank. If you get one of those larger exterior timers the turning mechanism may be stronger, allowing you to use larger syringes. This is one I have to try :)

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Giancarlo Podio
 

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In that case for larger doses you would be best to use a timing motor, I've salvaged a few from old dishwashers but they can be purchased cheap at surplus stores:

http://www.sciplus.com/category.cfm?subsection=18

There's models from 2rpm to 2rpd (revs per day for hour hand movement). They are usually very strong due to the large gear ratio used. I always wanted to make my own pumps with these but I didn't want to bother with the control circuit to change the speed in order to change the dose. This design on the other hand can accomodate various dosing volumes by changing syringe size and off-center position of the plunger without having to change the motor speed. Much easier to realize and adjust IMO.

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Giancarlo Podio
 

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The way I see it.... the timer just keeps turning, one revolution per day, meaning that for 12 hours the plunger is being pulled up (sucking ferts into the syringe) and the following 12 hours it's pushed down (sending the ferts into the tank). You can adjust the amount the plunger moves up and down by sliding the position where the plunger is connected to the rotating bar, the closer to the center the less vertical movement per revolution. But unless the motor is strong enough you likely won't be able to adjust it far enough off center to use the entire length of the syringe, so you may be better using a larger syringe and adjusting it to only use a small part of it. This would be a lighter load on the motor.

Giancarlo
 

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I can just see a V8 unit around the corner allowing you to dose everything individually :)

Regarding the syringes getting stuck, you will find that syringes are not made for long term use. The rubber plunger will loose it's lubricant rather quickly and will tend to get stiffer with time, meaning the likelyhood of it jamming up. I would suggest lubricating the plunger with silicon based lubricant, the same you use for O-Rings and pump impellers. Once a month should keep everything moving freely. It may even help get a larger syringe to work for you with the existing motor.

Giancarlo
 

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Timing motors or clock motors... they are used in washing machines, large clocks and just about anything else that needs a mechanical timer. Clock motors have a set speed and 1, 2 or 3 shafts for each hand of the clock, single hour hand motors would be perfect, many old train station style clocks used a single hour hand without a minute hand. Timing motors on the other hand come in various speed ratios, but they are all rather slow and very powerful as they often need to turn a large number of mechanical pieces. AC motors are best, they are cheap and the timing is kept accurate by the 110v frequency rather than having to use control circuits. The rest is just a lot of reduction gears.

Giancarlo
 

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Ruben, I would also suggest moving the pivot point of the syringe to the tip rather than half way up the syringe body. This will reduce the swinging of the tip where the hoses are connected to meaning less strain for the motor.

Giancarlo
 
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