The timer electronics controls a small electric motor which pushes a pin either in or out, depending on which way it turns. This pin is part of a pilot-operated solenoid type valve that switches the water flow on or off. If the motor turns clockwise (with normal power polarity, ie +ve to red), the pin is withdrawn, a drain is opened which relieves pressure on the diaphragm and water flows. If the motor turns anticlockwise the pin is inserted, the pressure relief drain is closed, and water pressure pushes the diaphragm and stops water flow. The electric motor is performing the function of the solenoid in the following diagram and has the advantage that no continuous electric power is required to hold it either open or closed.

A- Input side, B- Diaphragm, C- Pressure chamber, D- Pressure relief drain, E- Solenoid, F- Output side ¹⁾.

The motor is geared down by a gear ratio of 11 to 37.

This example is damaged, there is a little corrosion on the PCB and the LCD doesn't light up, although manual on/off control of the valve works.

The whole thing is held together via three screws, two in the battery compartment and one hidden under the front panel label. The label can be pealed off to reveal the screw.

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The water flow valve is operated by a geared motor that inserts or withdraws a pin that closes or opens a drain hole, that thereby depresses or releases the diaphragm that stops or releases water flow to the outlet.

• Holman CO1605 user manual.

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