Cylinder Drain Cocks

[D854_Tiger]

My understanding is that when a steam locomotive is stationary, for some time (how long?), any remaining steam in the cylinders can cool and condense.

 

When a locomotive starts to move under power (regulator opened), any water in the cylinders, which is non-compressible, could result in hydro lock and cause serious damage to the pistons, cylinders or even connecting rods.

 

For this reason, cylinder drain cocks are provided to force out any remaining water (and steam) when the locomotive first starts moving.

 

The drain cocks being closed once a sufficient amount of steam has passed through the cylinders to heat them to a temperature where no condensed water can result.

 

My question is are the cocks manually operated, linked in some way to the operation of the regulator, linked in some way to the motion of the valve gear or simply values set to open at some pressure above the normal operating pressure.

 

If the drain cocks are not linked, are any mechanisms or indications provided to prevent the driver from forgetting to open the drain cocks.

 

Also, how does this differ for superheated and non-superheated locomotives, indeed, in non-superheated locomotives saturated steam is partly water so how do they get round the non-compressible factor.

[Bulleidnutter]

My understanding is that when a steam locomotive is stationary, for some time (how long?), any remaining steam in the cylinders can cool and condense.

 

When a locomotive starts to move under power (regulator opened), any water in the cylinders, which is non-compressible, could result in hydro lock and cause serious damage to the pistons, cylinders or even connecting rods.

 

For this reason, cylinder drain cocks are provided to force out any remaining water (and steam) when the locomotive first starts moving.

 

The drain cocks being closed once a sufficient amount of steam has passed through the cylinders to heat them to a temperature where no condensed water can result.

 

My question is are the cocks manually operated, linked in some way to the operation of the regulator, linked in some way to the motion of the valve gear or simply values set to open at some pressure above the normal operating pressure.

 

If the drain cocks are not linked, are any mechanisms or indications provided to prevent the driver from forgetting to open the drain cocks.

 

Also, how does this differ for superheated and non-superheated locomotives, indeed, in non-superheated locomotives saturated steam is partly water so how do they get round the non-compressible factor.

I dont know how the American sprung loaded drain cocks work but UK practice tends to be a lever and mechanism by the driver and the drivers knowledge of when to open/ shut them.

 

If you ever get the chance. The BR black book is pretty much the bible on how to operate locos.

[LMS2968]

Cylinder drain cocks - known to enginemen as 'taps' - are manually operated by a lever in the cab, usually via a simple linkage but sometimes by a steam valve (Stanier pacifics used this due to the length and complexity of a linkage). The position of the lever was the indication, and the cloud of steam at the front end was another clue.

 

There were separate decompression (or cylinder relief) valves at the front and back of each cylinder to deal with any excess pressure within the cylinder, but water doesn't move that quickly, and neither the taps or decompression valves will always open fast enough to prevent damage.

Edited March 3, 2016 by LMS2968

[Blandford1969]

It's also worth adding that the taps are used if you get water carry over,(priming) which is shown either through droplets of water in the exhaust or a change in the sound - I cant really describe it well but looses its clear beat.

 

They can also be a blessed nuisance as when starting away on a cold morning with a cold engine with the taps open just adds to the fun of getting away without slipping. The taps can also then not close properly if bits of piston ring break off and get in the way of the mechanism.

 

The rule is if you leave an engine and get off the taps are always left open. Once on a train and the engine is warm you generally don't need to leave the taps open if only stopped for short periods of time. The thing I always find funny is that most companies had the operating mechanism at the drivers feet so to speak, but the LNER put it on the fireman's side.

 

I agree on the black book or for more detail 'Locomotive Management'

[BoD]

 If you ever get the chance. The BR black book is pretty much the bible on how to operate locos.

If that is officially called 'The Handbook For Steam Locomotive Enginemen' you can download the 1957 edition in various formats from here.

 

https://archive.org/details/HandbookForRailwaySteamLocomotiveEnginemen

[LMS2968]

I do have the printed version but that is definitely worth knowing!

[John Stubbington]

My understanding is that when a steam locomotive is stationary, for some time (how long?), any remaining steam in the cylinders can cool and condense.

 

When a locomotive starts to move under power (regulator opened), any water in the cylinders, which is non-compressible, could result in hydro lock and cause serious damage to the pistons, cylinders or even connecting rods.

 

For this reason, cylinder drain cocks are provided to force out any remaining water (and steam) when the locomotive first starts moving.

 

The drain cocks being closed once a sufficient amount of steam has passed through the cylinders to heat them to a temperature where no condensed water can result.

 

My question is are the cocks manually operated, linked in some way to the operation of the regulator, linked in some way to the motion of the valve gear or simply values set to open at some pressure above the normal operating pressure.

 

If the drain cocks are not linked, are any mechanisms or indications provided to prevent the driver from forgetting to open the drain cocks.

 

Also, how does this differ for superheated and non-superheated locomotives, indeed, in non-superheated locomotives saturated steam is partly water so how do they get round the non-compressible factor.

 

Hello, I used to be a Fireman in Steam days. I can confirm that the cylinder drain cocks are manually operated. My view is that they are often operated for too long a period when moving away on a heritage line to cause an impression?? Your mentioning of Super heating is something quite different and is a part of the boiler on a large engine. I hope this helps.

  John of 71A

[Phil Bullock]

It's also worth adding that the taps are used if you get water carry over,(priming) which is shown either through droplets of water in the exhaust or a change in the sound - I cant really describe it well but looses its clear beat.

 

They can also be a blessed nuisance as when starting away on a cold morning with a cold engine with the taps open just adds to the fun of getting away without slipping. The taps can also then not close properly if bits of piston ring break off and get in the way of the mechanism.

 

The rule is if you leave an engine and get off the taps are always left open. Once on a train and the engine is warm you generally don't need to leave the taps open if only stopped for short periods of time. The thing I always find funny is that most companies had the operating mechanism at the drivers feet so to speak, but the LNER put it on the fireman's side.

 

I agree on the black book or for more detail 'Locomotive Management'

 

One of the biggest skills for the fireman was/is to keep the water in the boiler at an appropriate level - sufficient to create steam for the requisite period of time without putting the injectors on when heavy work is required, but with enough room in the boiler to use the injectors when arriving/stopped in a station to put cold water in the boiler to prevent blowing off. Only learnt with experience. Getting it wrong and overfilling the boiler - or high levels of dissolved salts in the water, hence softening plants - leads to the priming Blandford describes.

 

Without wishing to belittle preservation footplate crews the work done is not going to give exposure to the extreme conditions steam sometimes had to operate under on the main line very often so crews dont gain the same experience - meaning that drain cocks are probably used more than they would have been, as insurance - who would want to take a precious preserved loco back to the depot with serious damage as a result of not using the drain cocks?

 

Phil

 

 

[ikks]

A very interesting thread.......Thanks to all concerned.

 

Mike

[Blandford1969]

One of the biggest skills for the fireman was/is to keep the water in the boiler at an appropriate level - sufficient to create steam for the requisite period of time without putting the injectors on when heavy work is required, but with enough room in the boiler to use the injectors when arriving/stopped in a station to put cold water in the boiler to prevent blowing off. Only learnt with experience. Getting it wrong and overfilling the boiler - or high levels of dissolved salts in the water, hence softening plants - leads to the priming Blandford describes.

 

Without wishing to belittle preservation footplate crews the work done is not going to give exposure to the extreme conditions steam sometimes had to operate under on the main line very often so crews dont gain the same experience - meaning that drain cocks are probably used more than they would have been, as insurance - who would want to take a precious preserved loco back to the depot with serious damage as a result of not using the drain cocks?

 

Phil

As a rule for me the taps are open going off shed, backing onto the train and then probably for the first hundred yards after which they stay closed, unless its very cold and the engine is standing for more than half an hour. Even then as soon as the regulator is opened the taps are closed. (mind you I was taught by a Saltley man and he expected very high standards.

[Mike Storey]

This is really interesting for me, as I will have a live steam loco with remotely operated, working, but simulated, drain cocks next year. So, all the experience being related on here will help me open and close the cocks in a more realistic manner.

 

Many thanks!

[IWCR]

Condensation is more of a problem with a non-superheated loco hence Drain Cocks will be used more often and after much shorter stops. This generally applies to older engines, often with slide valves.

A modern loco with Superheat and piston valves would as stated earlier not need to use the drains at all once warmed through unless a prolonged stand occurred during the working period.]

 

Pete

[PhilH]

Condensation is more of a problem with a non-superheated loco hence Drain Cocks will be used more often and after much shorter stops. This generally applies to older engines, often with slide valves.

A modern loco with Superheat and piston valves would as stated earlier not need to use the drains at all once warmed through unless a prolonged stand occurred during the working period.]

 

Pete

Locos with slide valves usually shouldn't need need constant use of draincocks as any trapped water should force the valve off its seat letting it escape.

[Davexoc]

 

The highlighted area is where taps actuator is on a GWR loco, in this case a mogul (at SVR). Pull the handle back to open, with a kick release to close.

 

Dave

[Blandford1969]

Locos with slide valves usually shouldn't need need constant use of draincocks as any trapped water should force the valve off its seat letting it escape.

I can only talk for Panniers and Jinty's but in my experience they don't need any more time with the taps open than any other engine.