I'm going to build a mechanism (as simple as possible) like the ballcock system used in flush toilet. But mine should be able to continuously discharge and refill automatically.

I already have a draft idea how to do it: referring to a classical ballcock system I would remove the handle and connect the lift arm to the flush valve flapper. In this way when the float reach the fill position will automatically trigger the discharge.

Before reinvent the wheel from scratch I wonder if this system has a specific name so I can find other resources or even products.

The goal is to discharge fixed amount of water every a given time. Playing with the geometry I should be able to define the interval of discharge and the amount of water to flush.

  • 3
    I’m voting to close this question because it's not about home improvement
    – Ack
    Aug 8, 2020 at 2:44
  • @Ack, I'm building an automatic irrigation system for my flowers. I thought this is about home improvement, it isn't?
    – Mark
    Aug 8, 2020 at 17:12
  • I reread your question 3 times to be sure: you never state what it is for, do you
    – Ack
    Aug 8, 2020 at 17:23
  • I stated that here above. Are you still sure I'm off-topic? I mean, should not be more useful to ask before? :)
    – Mark
    Aug 8, 2020 at 17:26
  • It's often helpful to describe the task and the approach so people know what you're doing so they don't VtC. Often, these vague questions end up being an XY Problem, though this doesn't seem to be. I'd think it's on topic here, but it could go to Gardening & Landscaping, as well.
    – FreeMan
    Aug 10, 2020 at 11:08

3 Answers 3


What about a "Pythagorean cup" style of device?

Pythagorean Cup diagram

from Wikipedia: https://en.wikipedia.org/wiki/Pythagorean_cup

The cup consists of a bowl with a tube in an inverted U-shape. Once the bowl fills beyond the top of the U-tube (step C above) it starts a siphon which drains the volume of the bowl until the siphon breaks. As long as the siphon flow is faster than the inflow, you'll have the behavior you describe - slow, continuous filling, and periodic discharge of a fixed amount of water. The bonus is that there are no moving parts!

As an aside, this is essentially the mechanism that powers the siphon in the bowl (not the tank) of the toilet...

  • That's exactly what I was looking for. I tried to sketch something like that, but I have to admit I am too dumb to design it, unfortunately.
    – Mark
    Aug 8, 2020 at 17:14

At a small scale (though you could easily scale it up) "tipping bucket" rain gauges basically do exactly that, with no valves needed. A tilted bucket fills until it alters the balance to the point that it dumps, and another bucket is moved in the stream of water.

A similar approach is used (one-sided) for the "bamboo noisemaker" type of fountain.

On a "typically larger scale" and with no moving parts, an autosyphon (also spelled auto siphon and possibly also known as a bell siphon - you'll have to ignore the beer-making results) will start itself and empty its "dose tank" all at once. They may be found elsewhere but I'm familiar with them from septic usage (rather than trickling effluent to the drain field at the rate of water use, it's built up to a "dose" of 50-200 gallons and dumped out the drain field all at once, which has some benefits.) This seems like a tolerably good, moderately in-depth read on them.

  • see also "cuba st bucket fountain" for another one-sided implementation
    – Jasen
    Aug 7, 2020 at 23:09

I too would suggest a siphon based system. if the in-flow rate is sufficient to reliably start the siphon.

If the flow rate is too slow then a vented loop system with an inverted ballcock or calibrated pressure-relief as the trigger.

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