piston valve steam loco 2 1/2″ gauge

[Chris KaminskiParticipant @chriskaminski64716]

I have drawings for two 2 1/2″ gauge locos with piston valve cylinders.

Martin Evans’s Black Five (in ME 1984)
and
Chris Barron’s 9F

Neither appears to have either drain cocks or relief valves?
Is this usual practice in this gauge? or am I missing something, please?
Are there any other published designs for piston valve cylinders in 2-1/2″ gauge?

[Nigel Graham 2Participant @nigelgraham2]

That does seem an odd omission. Relief valves seem rarer on model locomotives but drain-cocks are not, and perhaps more important for piston-valves than for slide-valves.

This is what Martin Evans says in his own book, on p.62:

All model locomotives about 1/2″ scale should be fitted with cylinder drain-cocks … at each end of the cylinder. They may be [operated] from the cab by … rods and cranks or Bowden cable.

 

The piston valve cylinders of large models are usually fitted with automatic water release valves above each valve head to prevent damage to covers by trapped water. They may [be] simple ball valves.

So he tells us not a great deal, but the boiler proportions table he gives on p.15 tells us 2-1/2″ gauge is 17/32″ scale… so over 1/2″ !

I would not like to say how easy they would be to make without looking ‘orribly over-scale, though.

…

Evans, M. “Manual of Model Steam Locomotive Construction”.

[Clive Brown 1Participant @clivebrown1]

In “Shop Shed and Road” LBSC recommends designs for discreetly mounted automatic relief valves for what he suggests are small cylinders of around 3/4″ bore.

In my experience of Martin Evans designs, such as it is, he cannot be relied upon to include every small detail in his drawings. Some things are sometimes left to the builder

 

[Nigel Graham 2]

On Nigel Graham 2 Said:

That does seem an odd omission. Relief valves seem rarer on model locomotives but drain-cocks are not,

….

So he tells us not a great deal,

Yes, Martin Evans is as usual vague and details are missing from published designs….

The only detailed (and excellent) information about cylinder drain cocks in 2 1/2″ gauge comes from John Baguley:

https://modeng.johnbaguley.info/locos/25inch/Helen%20Longish/helen13.htm

[Clive Brown 1]

On Clive Brown 1 Said:

In “Shop Shed and Road” LBSC recommends designs for discreetly mounted automatic relief valves for what he suggests are small cylinders of around 3/4″ bore….

and yet, even in 3 1/2″ gauge LBSC only shows drain cocks, without using relief valves?

[WearyParticipant @weary]

The LBSC ‘automatic relief valves’ are in-fact automatic drain valves.

Unusual to see a small gauge locomotive fitted with true ‘cylinder (over) pressure relief valves’ due to constraints of space/size/scale and making reliable working fittings.  It has been done though.

You should fit drain valves to  your piston valve locomotive, this will much reduce the chance of cylinder damage upon cold-start.   Automatic cylinder pressure relief valves can be fitted if you wish.

You may wish to pose your question over on Model Engineering Clearing House forum, under ‘General’ Heading as John Baguley, who you may know from the 2 1/2″ gauge society, is an active member there.

In addition one of the active members (‘Roger’) has recently described his cylinder relief valves in his build thread about a 5″ gauge ‘Speedy’.

Phil.

 

 

[Weary]

On Weary Said:

The LBSC ‘automatic relief valves’ are in-fact automatic drain valves.

That makes sense – thank you for clarifying

On Weary Said:

You should fit drain valves to  your piston valve locomotive, this will much reduce the chance of cylinder damage upon cold-start.   Automatic cylinder pressure relief valves can be fitted if you wish.

I totally agree with you about the need for some drain/relief valves,

hence my surprise that published plans/articles don’t even mention or suggest it.

Are you saying that “Automatic cylinder pressure relief valves” can be used instead of drain valves?

I like this idea because LBSC’s ‘automatic relief valves’ are easier to conceal in smaller gauges.

On Weary Said:

In addition one of the active members (‘Roger’) has recently described his cylinder relief valves in his build thread about a 5″ gauge ‘Speedy’.

Phil.

Yes, I follow this thread 🙂

 

[WearyParticipant @weary]

Hi Chris,

In theory cylinder pressure relief valves can be used instead of drain valves….

….. However ……

Cylinder Drain Valves are so simple that they are easy to test and maintain and unlikely to fail, however, Automatic Pressure Relief Valves are small, fiddley (in ‘our’ sizes),  tricky to maintain and test in situ, and thus liable to fail!   Drain Valves are preferable to Automatic Pressure Relief Valves if you are fitting one or the other.  I didn’t mean to suggest that the two fittings are interchangeable – they actually perform different functions.

There is a thread on the subject of Automatic Drain Valves here.

Phil

 

[Weary]

On Weary Said:

thanks for (very good) link.

I have also found this thread (where John B) comments on standard 2 1/2″ gauge practice

https://modeleng.proboards.com/thread/15615/cylinder-relief-valves

[Author]

Posts