Problem with taper plug cocks.

[ron]

Hi All
I've a boiler fitted with a 3 cock gauge column, the cocks are taper plug valves and what I find is, if the plug is tight enough to stop drips it's almost impossible to move and if they're slack enough to operate easily they leak, I tried lapping them with T-cut but if anything it made them tighter, anyone got any suggestions as to a lubricant for the taper.
Ron

[baggo]

Hi Ron,

In his articles on making small boiler fittings C R Amsbury suggests a smear of Molyslip now and again. Not sure if that's still available but probably Molybdenum Disulphide grease may be a suitable substitute as this impregnates the surface of the metal and forms a lasting lubricant. Don Young used to recommend it for fitting piston valves. You could try PBC (Poly Butyl Cuprysil) anti-seize compound, also known as Copperslip). Just a couple of suggestions.

I think a lot depends on the angle of the actual taper. Amsbury recommended 8 degrees as a compromise between freeness and steam tightness.

John

[jackrae]

I'd suggest a dry lubricant.

How about graphite dust as sold by locksmiths. If you "lap" this into the plug enough should become embedded to provide a lasting lubricant

Jack

[ron]

I came across a tube of VHT graphited lubricant called 'Thread Guard' in my cupboard of 'things that will come in handy one day', last night I took the plugs out and greased them with this and fired up the boiler this morning, it looks like a solution, both the main cocks are dry and although stiff are usable, the drain cock dribbles a bit after a blowdown but more or less takes up with the heat so possibly a little more lapping will help, thanks for the suggestions.
Ron

[steammadman]

Ron,
Take the lead out of a pencil , lay it,the lead on a sheet of white paper
and lightly scrape the lead with a pen knife,or stanley knife blade along
the length and you will have the perfect solution, a small pile of good
graphite dust, i think you know the rest.