As far as I recall, the lid on Youd's Level is opened from the outside with a key but can be opened without one from within. I can't for the life of me remember anything about the mechanism however.

Does anybody know how it works or even have a photograph? :flowers:

Ta!

They usually keep a key at the pavilion.
Its just a length of steel rod with a 90 degree bend in the end, about inch and half. This engages the latch inside so you lift the latch and then the lid in one go.

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I know how the mechanism works, whether I can describe it clearly is a different matter but here goes....

The latch consists of two long bars joined at either end with "L" shaped pieces, which have hinge attachements at the corner onto the lid. When closed, the L will be upside down with the upper bar catching on a pair of hooks attached to the frame. In this position, if you pull on the lid it just pulls the upper bar tighter against the hooks so the lid won't open. If however you have the "key" which is simply a hook to pull on the lower bar, the L then pivots so the upper bar is clear of the hools and the lid opens. Likewise, to open from below you just push on the lower bar then lift the lid. That's basically it though I think there are some finer points to it like which way round the pivot works, I'll have to go and have a look at the Youds lid at some point, or the Old Ash shaft which has the same closure.

It's a simple yet effective means of closing a shaft lid which has big advantages over nuts and bolts in that you can "lock" it once you're in so preventing passing grockles opening the lid and falling in, or locking you in....

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As one of the designers of the device, I would say Adam's description is about right.
All you need is something like a 6mm rod with a hook bent on the end. A welding rod will do at a push.
Poke it through the key slot and fish for the bar below and pull up.

Les

Thanks for confirming I've remembered correctly Les, at some point in the future I'd like to convert the Whale Sough lid to this system, not that many people will be keen on the crawl beyond! One question, does the lower bar need to be heavier than the latching bar for the lock to work properly or does the assymetry of the L-pieces ensure the latch tends to the shut position?

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We had to modify the design a bit by adding extra weight to the opening bar. As it is at 90 degrees to the latches, it is the weight of the opening bar that gives the turning moment to the mechanism, keeping it locked.