Auto Dosing

[jcali10]

Hello everyone. I finally got everything needed to set up a DIY auto doser. Strange thing happened when I was testing it out.

I ran the pump 10 times at 1 minute intervals, using water only, and the doses dispensed varied.

The first 5 runs dispensed 130 to 135 ml of water. The next 5 runs dispensed around 100-110 ml of water.

I have a little Mini 606 pump, with a syringe and tubing connected to it. I did not seal the connection where the syringe sits on the pump output. It snug but probably not watertight.

Could that be causing the varying results.

[krisw]

I think it's normal to have some differences. Just to be sure, the output end of the airline stayed at a constant height through all of your tests, right? And that was position in the tank where it would be once you're all setup and done? Part of the idea of the auto doser is keying on averages anyways, so at the end of the week, the amount of ferts going into the tank is the same regardless. In fact, front loading it a little bit like you experienced, might not be a bad thing anyways.

[jcali10]

I had the container in the cabinet under the tank, and the tubing taped to the top of the tank. It was positioned where it would be once operational.

I was thinking about placing some silicone sealer around where the pump and syringe meet to see if that has any effect.

Why does the pump push less water out when the water level in the container gets lower?

[Jeff120]

That is a pretty small variation, I wouldnt worry to much about that

[JMLenke]

I had the container in the cabinet under the tank, and the tubing taped to the top of the tank. It was positioned where it would be once operational.

I was thinking about placing some silicone sealer around where the pump and syringe meet to see if that has any effect.

Why does the pump push less water out when the water level in the container gets lower?

IIRC something about less weight pushing the water into the pump, the pump actually has to work harder with a lower level.

[maddog10]

Head pressure. A 1 foot tall column of water creates 0.434 psi at its base, or there about.

[jcali10]

So that's what head pressure is. So as the water column gets lower so does the pressure.

[SCMurphy]

"Head" is the difference in the surface level of the container and the point at which the liquid leaves the 'pipe'. So as the level of the container drops the head increases as long as the pipe releases higher than the surface level (it better or you'd have a siphon.) If you can raise up the container while keeping the outlet above the surface level of the liquid you will find a more consistent output from your pump.

[jcali10]

Actually I can place the container on a window sill above the tank. I think I will re-test it from that vantage.

Thank you all for your thoughts and ideas.

[krisw]

I would caution about using it above the tank. You don't want a siphon to dump the entire container of ferts into the tank.