Water switch

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Outline sketch

A water switch or differential pressure switch is a component of a gas flow heater that opens and closes the main gas valve due to a pressure difference.

The water switch consists of a capsule and a venturi nozzle. The capsule is divided into an upper and a lower half by a membrane . If water flows through the water switch, the water must also flow through the Venturi nozzle. As the water flows through the Venturi nozzle, negative pressure is created at the narrow point of the Venturi nozzle. At this narrow point there is a hole and a thin channel to the upper membrane chamber. As a result of the negative pressure, water flows out of the upper membrane chamber through the channel and the bore. This lifts the membrane. The diaphragm is connected to the main gas valve via the valve pin. The movement of the diaphragm opens and closes the main gas valve via the valve pin. A special variant of the water switch is shown in the schematic diagram. The connection channel between the narrow point of the Venturi nozzle and the upper membrane chamber contains a small ball. If water flows out of the upper membrane chamber, the ball is pushed downwards. The ball reduces the cross-section of the channel. This means that the water can only drain off slowly in a defined manner. This will slow down the opening of the main gas valve. The slow opening of the main gas valve ensures that deflagration cannot occur. Therefore this variant of the water switch is called "slow ignition valve". Water switches without a ball are used in electric instantaneous water heaters.

Individual evidence

1. ^ Vaillant (ed.): Warm water geyser MAG teaching material . 1995th edition. 1995.