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ruben 01-04-2005 01:00 PM

Fertilizer Dosing pump
This is a very simple project that I developed, Eheim products are horribly expensive in Mexico, It was improved by Ruud and now published (in Dutch) in his pages.
All you need is a timer, syringes, 2 check valves, a "T", small screws, pieces of sheet metal, some spare time.
I didnīt use the aluminum Ruud used as a base for the syringe but instead used a piece of PVC tubing (A Dremel tool help me carved it). A small screw works as a pivot (placed where "Rotate" is) I use a piece of sheet metal instead of that strange beige thing
A check valve in one side allows the fertilizer to go into the syringe, another one allows the fertilizer to go to the aquarium
Terumo syringes work better than BD, I tried all sizes from 60 ml to 1 ml, only 1 and 3 ml worked fine, bigger ones stuck, the injection cycle lasts 12 hours

Here's a photo (from Ruud pages)

gpodio 01-04-2005 01:18 PM

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 :-)

Giancarlo Podio

ruben 01-04-2005 01:23 PM

I tried a bigger timer but to my surprise the electric motor is the same as in the small ones

gpodio 01-04-2005 01:38 PM

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:

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.

Giancarlo Podio

ruben 01-04-2005 01:50 PM

That's a good idea, I just have to find one :D

Raul-7 01-04-2005 02:29 PM

Ingenious idea! But how do you attach the screw to the base of the syringe? Just say you need to dose 8mls per day, would you need an 8ml syringe? And when you say the "injection cycle lasts 12 hours", does that mean you have to reprogram the timer everyday?

gpodio 01-04-2005 09:18 PM

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.


ruben 01-05-2005 08:13 AM

You're right it only fertilizes half of the day, no reprograming is necesary the timer just keep going
As I tried to explain in the original post, I made a sleeve with a piece of PVC pipe, this is where you place the screws and attach the syringe, I forgot my camera today but I'll add some photos tomorrow.
With this kind of timer you can't dose 8 ml, the logical way was to use a 10 ml syringe which I tried (also tried 5, 20, and 60 ml), but is not reliable, it gets stuck frequently due to the lack of power from the small timer motor, if you can find a bigger one (like gpodio suggests it may work), this small timer can work with 1 and 3 ml syringes, they can deliver 0.1 to 0.7 ml (1 ml syringe) and 0.5 to 2.4 ml (3 ml syringe)
You should try with different sizes and brand names, not all of them work, some stuck quite easy (BD), for me Terumo worked, but I don't know if we have the same products
Another idea, if you find a bigger motor, why not 2 opposing syringes? (Like a BMW motorcycle engine) it may work and you have all day dosing, or dosing 2 different fertilizers

As you have already noticed, English is not my mother tongue, so feel free to edit the post, saludos desde Guadalajara
By the way I haven't seen yet an American (U.S.) posting in Spanish, why don't you try ? :D

gpodio 01-05-2005 11:05 AM

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.


ruben 01-05-2005 12:01 PM

A V8 sounds nice, but looking at my car (V12 Jaguar) I see a better option :lol:

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