In message .com,
Chippy writes
David 'Arsehole' Hansen wrote:

One way such systems can fail is if the arm breaks off. This risk is
controlled by not having arms generally not striking trainstops and
so not suffering the fatigue this involves. An arm at the front of
the train will only strike a trainstop on rare occasions.

One of the benefits of
trip cocks is that they are a very simple system.
Aren't they tested on every trip? They certainly used to be.
--
Clive