Lock for timed shower taps

[JumbleDuck]

At a campsite in North Wales this year . Brand-new showers. Holding the button in STILL only gave you the allotted time until released and pressed again! Purely mechanical/pneumatic.

Sounds like the ones in a local swimming pool: the water is cut off when the button is all the way in. So you press it in, then you use the plastic key strap from your locker to hold it 3/4 of the way in and you can shower as long as you like.