Can anyone point me at technical drawings for Prime Co. steam operated cylinder cocks? This is what was used on the C&NW #1385.
Thanks! in advance!..........mld

Found this on the interwebs, though I am not technically adept enough to know if it will help you: https://www.nwhs.org/archivesdb/detail.php?ID=58124

It is more than we had and every bit helps. Thanks............mld

It does not look like a steam operated cock. It looks like a simple pressure release at a fixed pressure.

It also looks like at mid pressure it will blow through, but at high pressure it will seal, so it is a form of automatic release for small amounts of condensate, but not a controllable full blow cock from cylinders. A lot of engines had this, as addition to manually controlled cocks.

Steven, this is where we will disagree on some points.
As they were applied in service on the #1385 the male thread portion of the body was screwed into the cylinder.
The small hole on the flat in the main body is where the steam supply pipe was threaded. There are 2 flats so the other side received a pipe plug.
Looking at the "exploded view" middle picture, when no steam was supplied the spring will push the "valve" up off its seat and allow steam & water from the cylinder to flow through the series of holes drilled in the cap and out the drain to atmosphere.
The cone shape of the smaller diameter of the valve mates to a similarly shaped seat that is machined in the cap much like a globe valve and seat.
The larger diameter portion of the valve is actually a piston that is machine fit into a cylinder in the main body. That cylinder communicates with the 2 small threaded holes on the flats and when steam is applied the valve is forced down onto its seat and closes the cylinder cock.
The main body is a very clever casting in that there are passages around the outside of the valve cylinder to allow the water and steam to flow from the engine cylinder, around the valve cylinder and then down to the holes in the cap.
There is also a tiny pilot hold drilled in the valve to allow a constant but metered flow from the steam line to the atmosphere. This keeps the water drained out of the steam line and also prevents freeze-up of the steam supply in winter.
I know this as I used these cylinder cocks on the #1385 while she was still in service.

Where we can agree is that it is a semi-automatic device. If you get a slug of water theoretically the hydraulic pressure applied through the drilled holes to the valve would overcome the steam pressure holding is shut. This would force the valve up into its cylinder and open the drain cock to hopefully prevent damage............mld

Strasburg may sell new versions of these ("Prime-type cylinder cocks made brand new"): https://mechanical.strasburgrailroad.co ... facturing/ Someone was selling a half-dozen used ones in March of this year: https://www.chaski.org/homemachinist/vi ... p?t=113331

I saw those on Home Machinist but they are SuperScale and made for either 1" or 1 1/2" to the foot scale equipment. They are great reproductions but I think they may be just a bit shy on relieving capacity for us. Thanks.........PD

So what is wrong with the old ones Pete? Are they broken or deemed not rebuildable? Just curious. Regards, John.

Hi John,
As the saying goes, they were "working when removed". I don't know of any issues but it would be good to find drawings that show what they're supposed to be..............mld

If the spring is still good, the critical thing is to lap in the valve seating surfaces. Don't overthink this, they are very robust.