Cylinder cocks

[britannia]

I am due to have my 5 inch STD 4 tank into the workshop for work on a number of items.  The current cylinder cocks are steam operated from the cab, but the arrangement under the cylinders is somewhat bulky and unsightly to be frank.  This arrangement also fouls the front bogie on tight curves due to it's size.  So I am considering options which include simple auto drain cocks which I have seen a design for - a small horizontal tube under the cylinder, with a ball (no spring).   Under operating conditions the steam in the cylinder pushed the ball up against the exit pipe in the end of the tube.  Any thoughts?  Otherwise, does anyone have a neat design for steam operated cocks?  

[stevep]

I think that steam operated cocks need a spring to keep the ball OFF the seat (i.e. open). When steam is applied to the cylinder, the steam pressure closes the ball on to the seat, and when the steam is removed, the cock opens again.

Personally, I prefer manually operated cocks, as you can keep them open and apply steam to warm the cylinders. In fact, on my Stanier, I always pulled away with the cocks open, closing them when we were under way.

[Gary L]

Feb 8, 2022 15:53:01 GMT stevep said:

I think that steam operated cocks need a spring to keep the ball OFF the seat (i.e. open). When steam is applied to the cylinder, the steam pressure closes the ball on to the seat, and when the steam is removed, the cock opens again.

Personally, I prefer manually operated cocks, as you can keep them open and apply steam to warm the cylinders. In fact, on my Stanier, I always pulled away with the cocks open, closing them when we were under way.

Entirely agree with Steve. That is how locos were driven in full size, and the reasoning is good. It is said to slightly reduce the likelihood of slipping on the first movement of the wheels too, though that is a bit arguable.

If a tidy and inconspicuous mechanism is required, there is a lot to be said for the LBSC method of piano wire inside a fine copper tube. It isn’t prototypical in most cases, but it is much easier to arrange than bell cranks and rods which was the usual method in full size, and it works well.

HTH

Gary

[andyhigham]

These are the drain cocks on my Baldwin.
They work the other way around to normal steam drain cocks, ie steam to open. They are 3/8" diameter x 5/8" long. there is a ball on the top which seals by cylinder pressure. A little piston with a pin on it pushes the ball up.
20220208_160508 by Sigma Projects, on Flickr
20220208_163148 by Sigma Projects, on Flickr

[stevep]

Andy - that's a nice twist, because you can keep the cocks open when you crack the regulator. (Steam pressure in the cylinder being less than full boiler pressure).

[andyhigham]

If the design was turned through 90deg it could function as an automatic cock which could be overriden to the open position

[don9f]

The BR Standard steam operated cocks have springs to hold the valves off their seats.....ie “open” to drain condensate from the cylinders. When required, the driver opens a control valve that feeds live steam to pistons within the cocks that close all the valves. Under all normal conditions, steam pressure in the cylinders will not overcome the force keeping the valves closed. Thus the cocks can be open for as long as needed to clear the condensate, regardless of regulator opening.

Right, now although they are fiddly to machine and make work reliably, the Doug Hewson castings available from The Steam Workshop, are scale replicas of the real things and really look the part, should you wish to go down that route! I have them on my 9F and I fitted them a while ago to replace the original, Les Warnett ones that also looked bulky etc. etc. (although they did work well).

Unfortunately the relevant photos that were in my 9F thread were on Photobucket and have long since disappeared, but I could probably find the originals if needed....

Cheers   Don

[andyhigham]

A quick sketch. This would function as an automatic drain cock with no steam applied. if steam is applied it would hold the ball off its seat allowing water and or steam past.
20220209_093144 by Sigma Projects, on Flickr

[flyingfox]

Greetings, this is a copy of a post I made recently relating to another topic.

I have been a fan of steam operated drain cocks for some time, first using them to avoid complex coupling and rodding arrangement to a 3 cylinder locomotive, just steam pipes.
As far as the operating valve goes, I use a on/off screw down valve to put them on, and fix a Don Young type condensate drain valve in the cock steam supply pipe after the on/off valve. This valve consists of a ball, with a light spring under it to open it, and it is closed by the steam being applied via the on/off valve. I usually mount this drain valve on the manifold where the steam feed to the cocks splits to each cock. As soon as the steam is shut off to open the cocks, the pressure rapidly reduces, due I think to condensation, and the lightly sprung ball lifts off its seat to drain the remaining pressure.
All simple to make, connect up, and woks well. The valves still act as pressure relief valves, and only close when you apply pressure via the valve.
Regards
Brian B

[pault]

Hi
A very simple type of steam operated drain cock I have seen used many times is simply a flat face with two drillings in the face. One to the outside world, the other into the cylinder. The face forms the end of a cylinder with a PTFE piston which is pushed up against the face by steam from a valve. No springs, pushed open by steam or water, so lets water out on a cold engine. I'll try and sketch it out.

[britannia]

Feb 10, 2022 20:33:18 GMT pault said:

Hi
A very simple type of steam operated drain cock I have seen used many times is simply a flat face with two drillings in the face. One to the outside world, the other into the cylinder. The face forms the end of a cylinder with a PTFE piston which is pushed up against the face by steam from a valve. No springs, pushed open by steam or water, so lets water out on a cold engine. I'll try and sketch it out.

 
A sketch would be helpful thanks

[robmort]

Automatic draincocks are the simplest solution with no need for an operating mechanism. They are reliable and can be made very small and unobtrusive.

They can even be built in to the cylinder wall to make them invisible.

An even simpler and neater design for an automatic drain cock is like a simple vertical clack, with the ball being of silicon nitride that floats when water is present at zero pressure, then seals at steam pressure. This is the same principle as that used to drain condensate in vertical steam brake cylinders such as those described by Don Young, but with improved ball material.


draincock by rob1524, on Flickr

[pault]

Feb 16, 2022 10:34:12 GMT robmort said:

Automatic draincocks are the simplest solution with no need for an operating mechanism. They are reliable and can be made very small and unobtrusive.

They can even be built in to the cylinder wall to make them invisible.

An even simpler and neater design for an automatic drain cock is like a simple vertical clack, with the ball being of silicon nitride that floats when water is present at zero pressure, then seals at steam pressure. This is the same principle as that used to drain condensate in vertical steam brake cylinders such as those described by Don Young, but with improved ball material.


draincock by rob1524, on Flickr

Unless I am missing something you are going to need a spring to make a Silicon Nitride ball float.

[robmort]

Feb 16, 2022 16:58:20 GMT pault said:

Unless I am missing something you are going to need a spring to make a Silicon Nitride ball float.

No, the ball "floats" or lifts enough, even if it's steel or bronze, to let the water escape, as Don Young explained.

[pault]

Feb 16, 2022 19:41:04 GMT robmort said:

Feb 16, 2022 16:58:20 GMT pault said:

Unless I am missing something you are going to need a spring to make a Silicon Nitride ball float.

No, the ball "floats" or lifts enough, even if it's steel or bronze, to let the water escape, as Don Young explained.

I would be very interested to see the explanation, as it seems to go against the laws of physics. If indeed the ball floats, why doesn't the ball in a clack float and let the water out?

[doubletop]

I have no idea where this came from but the filedates say 2007. I have them on a 5" Simplex and 7.25" Dart, they work well. HP steam holds them closed as the cylinder pressure is never (rarely) the same aa the boiler pressure. Removing the control steam allows the cylinder pressure to open them.



The only problem I have is when I forget to shut down the control steam before blow down at the end of the dat. I have a short length of piano wire I poke up the holes to open them.

I use a variant of the control valve Terrance Holland published in ME in his Fairly Complex series in 2012. On the Simplex it is a push/pull knob comming out of the cab floor. On the Dart it is coupled to the original mechanical drain cock lever.

Pete

[Gary L]

Feb 17, 2022 20:19:53 GMT pault said:

Feb 16, 2022 19:41:04 GMT robmort said:

No, the ball "floats" or lifts enough, even if it's steel or bronze, to let the water escape, as Don Young explained.

I would be very interested to see the explanation, as it seems to go against the laws of physics. If indeed the ball floats, why doesn't the ball in a clack float and let the water out?

Interesting question. It is presumably a matter of displacement. Ceramic balls weigh little in air, even less in water. Even bronze balls would weigh a lot less in water, so I assume it is not enough to keep it in intimate contact with the seat, especially when surface tension effects are taken into account. I gather these auto drains work best at times when steam chest pressure is low. The ball in a clack is different, it is held in place by boiler pressure.

One of those ‘flying bumblebee’ questions perhaps? If it works, then don’t worry about the theory…

Gary

[robmort]

Feb 17, 2022 20:19:53 GMT pault said:

Feb 16, 2022 19:41:04 GMT robmort said:

No, the ball "floats" or lifts enough, even if it's steel or bronze, to let the water escape, as Don Young explained.

I would be very interested to see the explanation, as it seems to go against the laws of physics. If indeed the ball floats, why doesn't the ball in a clack float and let the water out?

Well it works even if it defies the laws of physics. Remember that the amount of water that needs to escape at each cycle of the piston is miniscule, so a slight unseating of the ball is enough, which is likely to happen with turbulence during each stroke as the pressure drops, particularly on the exhaust stroke. A clack has constant pressure and a tiny leak there is not noticed.