[modeleng] Re: Drain Cocks
- From: "Jeff D" <jeffdayman@xxxxxxxxxxxx>
- To: modeleng@xxxxxxxxxxxxx
- Date: Thu, 06 Nov 2008 12:18:11 +0000
I agree, the cocks should be made to take BP + a safety factor.
I too saw the article in EIM, but I am not clear how the individual ports
are sealed. I see there is an o-ring between each of the 4 ports, but
apparently no seal is used around each port hole (at least it is not
visible). To me, this would leak at least a bit, as there has to be some
clearance from valve dia to block bore diameter, whether the port is aligned
to the outlet or turned 90 degrees. With tapered drain cocks, the taper
takes up the clearance mentioned and so it seals without a port o-ring or
packing.
To seal the straight bodied valves, I would think an o-ring would be needed
around the ports also, but this would be a saddle shaped groove and quite
hard to machine, and the o-rings may cut where they cross the port edge.
Did I miss something? is there a floating PTFE bit or other seal?
Cheers Jeff Dayman
>From: "Peter Beevers" <peter@xxxxxxxxxxxxxx>
>Reply-To: modeleng@xxxxxxxxxxxxx
>To: <modeleng@xxxxxxxxxxxxx>
>Subject: [modeleng] Re: Drain Cocks
>Date: Thu, 6 Nov 2008 06:59:37 -0000
>
>Peter,
>
>Hmm, they will have to deal with steam at near boiler pressure - when they
>are closed, and steam is admitted into the cylinder on the power stroke,
>they will have to stay closed despite that pressure. Worst case, they may
>have to resist (for very short periods, when starting), almost 100% boiler
>pressure, depending on the efficiency of your steam circuit.
>
>In general, the pressure will be less - while running probably no more that
>30-40 psi.
>
>Hope this helps
>
>Peter
>----- Original Message -----
>From: "The Sheppard Residence" <psbr20252@xxxxxxxxxxxxxxxx>
>To: <modeleng@xxxxxxxxxxxxx>
>Sent: 05 November 2008 22:06
>Subject: [modeleng] Drain Cocks
>
>
>There was a very interesting article in the 7.25" news last time (I
>think) about a "centralised" drain cock system which I am currently
>building. There were no drawings, just a picture of the components and
>the assembled item.
>
>One thing I would like to do is test mine before I install it on the
>locomotive, the question is, what sort of pressure do the drain cocks
>have to cope with?
>
>It obviously isn't boiler pressure as by the time that they are in use
>the steam has done its work and it is being exhausted, but there must
>still be some pressure there.
>
>Does anybody have any idea how much (so I can set the air compressor
>accordingly).
>
>Cheers
>
>Peter
>
>
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