The ridge vent is open all the time, protected from the rain by a good sized capping and sealed with small wire mesh to keep out the rats, mice, possums and birds. It has worked well for 23 years without maintenance.
The ridge vent is a long slot about 1 sq.m. at the highest point of the roof (an important point) as the air at that point is at a lower atmospheric pressure level than at ground level. Acting in concert with the ceiling vents which, when opened from about 6pm after a hot summer day, allows lower density warm air from the interior to rise up and escape into the outside air.
This movement is assisted by the higher density cool air collected (mainly under the pergola vine on the north side) which rushes into the house when we open the doors and windows and cools the internal surfaces.
Doors, windows and ceiling vents are left open all night cooling all structural elements and are then closed again around 8-9am as the external air warms up for another hot day.
In this way we live in a mini-ice box for most of the day without the need for any air conditioning other than perhaps a personal fan if it gets really warm.
The roof space air is regarded as being part of the exterior rather than the house interior as the ceiling R6 insulation is the main thermal barrier at all times. This eliminates the need to have any air-tight closing mechanism which would be quite expensive. Simple closing mechanisms and flywire are provided by the ceiling vents (see MR 3).
It is a simple and cheap system to install which has no running costs, is completely silent in operation and can be left working from sunset to sunrise with no difficulties. I cannot understand why people are so tolerant of the expensive and negative side-effects of air conditioning.