What type of float operated valve has the outlet top mounted?

• A. Gate valve
• B. Diaphragm
• C. Ball valve
• D. Check valve

Answer: (B)

Float-operated valves used to fill a cistern come in two common forms: diaphragm and ballcock. The form with the outlet mounted at the top of the valve body uses a flexible diaphragm to regulate flow. As the water level rises and the float lifts, the diaphragm is pressed to reduce or stop the inlet, and water is discharged into the tank through that top-mounted outlet. This top-positioned outlet is a hallmark of the diaphragm design, which relies on the flexible membrane to seal against the valve seat.

In contrast, a ballcock uses a floating ball on a rod to operate the valve, and its flow and shut-off arrangement isn’t defined by a top-mounted outlet in the same way. Gates and check valves aren’t float-operated for automatic cistern filling; they serve different purposes—gate valves regulate flow manually, and check valves prevent backflow. So, for a float-operated valve with the outlet at the top, the diaphragm type is the best fit.