Understanding and Building the Aquaponics Bell Siphon Valve

The bell siphon is the heart of a flood-and-drain aquaponics grow bed. It automatically drains water after flooding, cycling several times per hour. Four components:

1. Drain Hole

In grow bed bottom. ¾–1″ PVC or bulkhead fitting. Accepts stand pipe.

2. Stand Pipe

Sets flood level (1″ below media surface). For 12″ bed, cut for 10–11″ water height.

3. Bell Cover

Larger pipe (2–3″) over stand pipe, capped top, notched bottom (1″ high). Creates siphon; breaks it when water drops.

4. Media Guard

Open tube (4–6″) with side slots. Keeps gravel away from siphon.

DIY Advantage

Cheap, simple, fun to build. Aim for drain time ≤ half of flood time. 3–4 cycles/hour typical.

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