What Is a Float-Operated Level Control Valve? Float Valve Types and Selection Guide
Is your tank overflowing, is your pump running dry, does the reservoir empty overnight? Most of these problems come from the wrong float device, or no float at all. This guide explains the difference between a ball float valve, a float-operated level control valve and a cable float switch, which one to choose for which tank, and what to watch during installation.
Short answer: use a mechanical ball float valve to shut off the inlet of small and medium tanks, a float-operated (hydraulic) level control valve for large tanks and supply lines, and a cable float switch to start and stop pumps by level.
Quick Selection Table
| Your need | Right product | Why |
|---|---|---|
| Shut off mains water when a roof or basement tank is full (1/2"–2") | Plastic ball float valves | No power needed, economical, easy to install |
| Level control in large tanks, reservoirs or supply lines (DN50+) | Float-operated level control valves | Works on line pressure, high flow, slow closing reduces water hammer |
| Float located away from the valve or adjustable level band | Electric float level control valves | Modular electric float with adjustable level range |
| Start and stop a submersible, booster or drainage pump by level | Cable float switches | Protects the pump from dry running and the tank from overflow |
| Steam boilers and conductive liquids | Level electrodes | Conductivity sensing, no moving parts |
1. How a Mechanical Ball Float Valve Works
As the tank fills, the float rises and, through its arm, closes the valve seat. When the level drops, the float falls and the inlet opens again. Plastic ball float valves are typically rated up to 6 bar; at higher mains pressure, install a pressure reducing valve upstream or the valve may not close tightly.
2. How a Float-Operated (Hydraulic) Level Control Valve Works
A diaphragm main valve is controlled by a small float pilot circuit and operated by line pressure, without external power. When the tank is full the pilot closes, pressure builds above the diaphragm and the main valve closes; when the level drops the pilot opens and the valve reopens. Benefits: high flow from DN50 up to DN200–DN250, gradual closing that reduces water hammer, long service life and manual override. In the electric float version, a modular electric float in the tank controls the pilot, so the float can be placed away from the valve and the level band can be adjusted.
3. How a Cable Float Switch Works
A ball inside the float moves when the float tilts and switches a micro switch. In fill mode it stops the pump when the tank is full; in empty mode it stops the pump when the water runs out, preventing dry running. If the pump current exceeds the switch rating, control the pump through a contactor and have a qualified electrician make the connection.
Installation Tips
- Fit isolation valves and a Y-strainer upstream of the level control valve.
- Install the valve according to the flow arrow on the body.
- Keep the float away from the turbulent inlet zone to avoid constant cycling.
- Drain the pilot circuit of outdoor valves in freezing conditions.
FAQ
Does a float-operated level control valve need electricity?
Mechanical pilot versions do not; they run on line pressure. Electric float versions need power only for the float and control circuit.
Up to what pressure does a plastic ball float valve work?
Typically up to 6 bar. Above that, install a pressure reducing valve upstream.
Let us help you choose: send your tank volume, inlet pipe size, supply pressure and goal (shut-off or pump control) on WhatsApp and our technical team will recommend the right product and size.