regulator pressure equalization

[rickhann]

List

I have built a regulator for A 3-1/2" Rob Roy per Martin Evans design. It calls for a small hole to be drilled into the tube containing the control rod. The hole is to equalize the pressure in the body of the regulator to that of the boiler pressure. I have been going through past issues of ME and have found several similar regulators of this type and they all show the equalization hole to be on the top of the tube. Why? My instinct would be to place the hole on the bottom to allow drainage of any condensation when the boiler is shut down. Is there a valid reason for the hole to be on the top, or is it where the draftsman decided to put it? Thanks in advance. I am relatively new to this group and to date, it has been a great source of information to me.
Rick,
Cape Cod, MA USA

[baggo]

Hi Rick,

I can't see any reason why the hole should be on the top either. When I made a similar regulator for Helen Longish I did actually drill the hole in the bottom of the tube for exactly the reason that you suggest - so that any water that gets inside the tube can drain out.

John

[gilesengineer]

It may be that a hole in the underside might be below the top water level(?), in which case you may get a build up of scale in there, which you wouldn't if you only get steam in there via a top hole.
Just a thought.

Giles