Name this bolt, please.

[Ron Nossaman]

> Just a "combi" boiler with the central heating pressurised to about 1 
> atmosphere, which I suppose is pretty normal.  Over time the pressure 
> drops and one has to raise it by opening the system to the main.  In the 
> old days you'd have a sturdy brass cock to turn open until the pressure 
> was right and then close.  This is now forbidden and is replaced with a 
> slotted screw, which one has first to find, then get a screwdriver 
> that's long enough to get past the pipes that are in the way.  You then 
> have to hold the tip of the screwdriver in the slot so that it doesn't 
> wander, while tuning the rather stiff screw a quarter of a turn, and 
> back again when you're finished.  If you don't fully close it, which is 
> easily done, then slowly the pressure in the system will rise to mains 
> pressure, probably leading to leaks and even bursting the heat-exchanger 
> and flooding the house.  No doubt if I read the regulations I'd discover 
> that I ought to take nil by mouth for 5 hours before the operation and 
> wear goggles and a safety belt to British Standard 5908-b.
> 
> JD

On this part of the planet, pressure in this type of 
(typically commercial) system is maintained automatically 
through a diaphragm regulator. No personal armor or tools 
required to schedule an annual maintenance inspection.
Ron N