Inside admission

[rodent279]

Can someone explain the terms inside admission / outside admission to me please, in relation to steam locos?

 

Cheers N

[PenrithBeacon]

https://en.wikipedia.org/wiki/Walschaerts_valve_gear

 

A simple internet query ...

[ForestPines]

I'm not sure that that Wikipedia article really explains the meaning beyond saying that they exist.

 

It is a description of how piston valves are arranged; it only applies to locos with piston valves.  With inside admission valves, the live steam enters the valve between the two pistons, and the exhaust steam passes through the ends of the valve, outside the pistons.  With outside admission valves it is the opposite: the live steam enters the valve at both ends, and the exhaust steam passes through the space between the pistons.

 

The reason it only applies to piston valve locos, incidentally, is that slide valves have to be outside admission, so that the pressure differential between live and exhaust steam acts to keep the valve steamtight.

[62613]

The disadvantage of outside admission is that the piston rod glands are subject to the full steam pressure,and the gland packings have to be arranged to suit this; inside admission has none of these difficulties. I would think that all 'modern' long-travel valves were inside admission.

Edited July 3, 2018 by 62613

[New Haven Neil]

The disadvantage of outside admission is that the piston rod glands are subject to the full steam pressure,and the gland packings have to be arranged to suit this; inside admission has none of these difficulties. I would think that all 'long-travel' valves were inside admission

 

Nope - ask Mr Bulleid!

[rodent279]

Thanks all, that explains it nicely!

[28XX]

Inside admission allows you to walk around inside the engine sheds and workshops, outside admission only allows you access to the open yard and walk between the buildings.

[peterfgf]

Nope - ask Mr Bulleid!

Indeed. I was looking at the sectioned rebuilt Bulleid pacific in the (National) Railway Museum in York last week and was slightly surprised that it was outside admission.  I also wondered at some of the open-ended drain pipes from the exhaust system.

 

Peterfgf

[rodent279]

Inside admission allows you to walk around inside the engine sheds and workshops, outside admission only allows you access to the open yard and walk between the buildings.

Ha ha!

[bigherb]

Indeed. I was looking at the sectioned rebuilt Bulleid pacific in the (National) Railway Museum in York last week and was slightly surprised that it was outside admission.  I also wondered at some of the open-ended drain pipes from the exhaust system.

 

Peterfgf

Although that was a hangover from the the way the original chain drive valve gear had to work.