[modeleng] Re: Automatic Drain Cocks

I haven't seen the article, but if it is as easy as you say, it must surely
have been done before.
If not, why not?

Might be worth trying one to see how well it works.
alan@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

www.alanstepney.info
Model Engineering, Steam Engine, and Railway technical pages.


----- Original Message ----- 
From: "Clif Walker" <clif.gwr@xxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Thursday, September 30, 2004 9:23 PM
Subject: [modeleng] Automatic Drain Cocks


Hi All,
I dont know if any of you saw the recent article in one of the Model
Engineering magazines regarding automatic drain cocks.I didn't see it myself
but I was sent a photostat copy of the design.
The article I believe was submitted by someone in South Africa and basically
consisted of a short horizontal tube with a loose SS ball in it, sealed at
one end and a hole at the other with a seating. A connection off of the top
of the tube was made to the cylinder as a normal drain cock would connect.
Now the idea seemed to be so simple and the best thing since sliced bread.
The principle explained was that when the tube filled with water the ball
dropped off of the seating and allowed the water to drain out,but when steam
entered the tube it's velocity pushed the ball along the tube and onto the
seating.
I made a couple of the said beasts and gave them a test by putting a bit of
plastic tube on the top connection,filling my mouth with water and then
blowing.I found that the initial water in the cock blew out but as soon as
an air bubble went through, the ball popped onto it's seating but would not
release untill all pressure was released no matter how much water was in the
pipe.
Now this is not good news for a drain cock as even on a exhaust stroke there
is still pressure in a cylinder,so it seems that these drain cocks would not
release no matter how much water was in the cylinders once the ball has
seated.
In such a small dia tube I do not see the difference in velocity between
water and steam being much different which is the supposed operating
principle.
I did think at the time that how something so simple not been discovered
before but has anybody else tried playing with these things?

Regards

Clif

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