About float valves
A float valve (FLV) closes or opens as water level in its reservoir goes up or down. Older types had a floating body and system of levers that converted its movements into closing and opening of the valve itself, as shown in the next figure.
Below its regulating range, the float valve is a minor loss; above it, the float valve is closed.
Float valve - preventing overspill
The upper limit of this range is slightly lower than the top water level of the reservoir. The regulating range of a float valve is usually around 0.5m.
Newer types are far more sophisticated, but the principle remains much the same. A float valve is placed in the inflow pipe of a reservoir. Typical arrangements are shown in the figure below:
Notes:
- A float valve can be positioned only on a reservoir inlet pipe.
- A reservoir may have several inflow pipes, each with its own float valve.
- A float valve cannot prevent the emptying of its reservoir.
- The effect of a float valve is felt only within its regulating range.
The non-return valve is closed during normal operation. It opens up only when pressure in the upstream node drops below the current water level in the reservoir, allowing stored water to return to the system.
Float valve arrangements
Backfeed pipe
The non-return valve in the backfeed pipe is closed during normal operation. It opens up only when pressure in the upstream node drops below the current water level in the reservoir, thus allowing stored water to return to the system. For example, if booster pumps are switched off, because the reservoir is full, and there is demand between the pump station and the reservoir, then a backfeed pipe is necessary to supply that demand.
Float valve characteristics
A standard characteristic of a float valve, relating local loss coefficient to the relative position of water level within the regulating range is included as a built-in curve that can be viewed from the Valve Curve Page of the Float Valve Property Sheet or from the Valve Curve Grid View of the Links Grid. Valve opening of 0% corresponds to the top of the regulating range and 100% valve opening corresponds to the bottom of the regulating range.
For details of the calculation of valve minor losses see the About valves topic.
Float valve characteristic
Local loss coefficient 
| Opening (%) | Closure (%) | DefaultFLV | |
|---|---|---|---|
|
1 |
0 |
100 |
Fully Closed |
|
2 |
0.2 |
99.8 |
1e12 |
|
3 |
2 |
98 |
10e9 |
|
4 |
4 |
96 |
100000 |
|
5 |
10 |
90 |
5012 |
|
6 |
20 |
80 |
1202 |
|
7 |
40 |
60 |
250 |
|
8 |
60 |
40 |
50 |
|
9 |
80 |
20 |
10 |
|
10 |
100 |
0 |
2 |
