Yes because in order to close most doors, extra force is needed at the end
to overcome the latch friction, so it can seem that it almost closes and
rests on the latch then suddenly it will close the last bit when it
overcomes the friction.
Brian

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The Sofa of Brian Gaff...

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"Dave Liquorice" wrote in message
idual.net...
On Mon, 09 Sep 2019 11:37:25 +0100, Mike Halmarack wrote:

My flat door, which is a fire door has a Briton 121 CE door closer.
I can quite crudely adjust the closing speed but the latching action
adjustment screw seems to have little or no effect on the last 15
degrees or so of closing.

Is this a new closer or one that has been in use a while and might
have been "adjusted" by others?

I think they work by a simple "cone in hole" flow restictor for the
oil inside with the outlet for the "closing" speed blocked off when
the door gets to the "latching" position. If the latching adjustment
is very open then the closing speed adjustment won't work well and
it'll latch quickly.

I'd try gently(*) adjusting both to the slowest closing you can get,
then slowly increasing the closing speed (1/4 turn at a time) to
something suitable, then increase the latching speed. This may well
also increase the closing speed a little so that might need tweaking
down a bit.

(*) You don't want to damage the cone or seat otherwise the
adjustment becomes rather to coarse. If this closer has been "got at"
before maybe this has already happened? If it goes from tortoise to
mouse trap in less than a turn it's buggered.

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Cheers
Dave.