# Float valve: how it works, how to choose and fit one in a tank

> How a float valve works, the difference between lever and diaphragm models, how to choose a float and set the water level in a tank.

Web page: https://watertrade.com.ua/en/articles/article/poplavkovyj-kran-ustanovka · Other languages: [UA](https://watertrade.com.ua/articles/article/poplavkovyj-kran-ustanovka.md), [RU](https://watertrade.com.ua/ru/articles/article/poplavkovyj-kran-ustanovka.md)

*September 16, 2026*

![Diagram: water tank, float valve on the inlet, lever with a ball float and the water level](https://watertrade.com.ua/uploads/articles/float-valve-install.jpg)

A float valve fills a tank and shuts off the water by itself when the tank is full. It is used in storage tanks, irrigation containers, livestock drinkers, pools and cisterns. It needs no electricity: the float rising with the water does all the work.

## What the diagram shows

1 — the valve body on the inlet pipe, 2 — the lever, 3 — the float, 4 — the working water level set by the length and angle of the lever.

## Types

- **Lever (piston) valves** are simple and reliable and suit pressures up to 5–6 bar. Larger sizes need a bigger float.
- **Diaphragm valves** close smoothly without knocking and handle higher pressure. Good for high-pressure mains.
- **Valves with pressure regulation** work at up to 12 bar and can be fitted directly to the mains.

## How to choose

1. **Size** — match the inlet pipe: 1/2" for barrels and tanks up to 500 L, 3/4"–1" for containers of a cubic metre and more.
2. **Pressure** — check the supply pressure. Above 5 bar, choose a diaphragm valve or one with pressure regulation.
3. **Float** — a large valve needs a larger float, otherwise it will not have the force to shut off the flow. Copper and stainless floats outlast plastic ones; for hot water use metal only.

## Installation

1. Drill a hole in the tank wall 5–10 cm below the top edge, above the planned water level.
2. Insert the valve and tighten the nuts with washers on both sides of the wall.
3. Screw on the lever and the float and connect the supply.
4. Turn the water on and see where the valve closes. To raise the level, bend the lever up or move the float; to lower it, do the opposite.
5. Always fit an overflow pipe just above the working level in case the valve fails to close.

> If the valve knocks when it closes, fit a pressure-regulating valve in front of it or replace the lever valve with a diaphragm one.

Pick a valve and a matching float in our [float valves](https://watertrade.com.ua/en/catalogue/krany-poplavkovye) and [floats](https://watertrade.com.ua/en/catalogue/poplavki-dla-poplavkovyh-kranov) sections.

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