'Free-Wheeling' a Steam Loco?

Hi there, all,

Some time ago there was a TV programme about two UK-built locos being repatriated. They didn't travel under their own steam but were included in 'trains of opportunity'.

For some reason (maybe the result of over-festivity!) the thought I had then re-surfaced a few days ago:

How do you 'free-wheel' a steam loco? The pistons are still coupled to the wheels, there's no clutch. I can visualise that what was the exhaust stroke would proceed although there would be fluid dynamic losses. I can't understand how what was the power stroke proceeds - where does it get its air to fill the cylinder?

And, what about lubrication?

Best regards,

Swarf, Mostly!

Hello,

Generally the connecting rods will have been removed as part of the preperations before moving the locomotive.

Regards,

Bob

I thought that they uncoupled the pistons at the cross head so that it freewheeled.

I recall seeing numerous photos of of locos being towed to scrap yards at the end of the steam era in the UK and the coupling rods were invariably tied to the running boards or thrown in the coal space in the tender. Whether this was done to reduce the amount of rolling resistance as some of these trains were several dead locos long, or whether some bright spark was thinking of the future preservationists !

Typically I can't find any photographic examples at present but I'm sure someone here will support or refute this.

Phil

Wild guess - are boilers fitted with a valve to prevent a vacuum forming when it cools down after work? If so, free-wheeling a cold engine would pump air out of the boiler and the valve would open. As the pressure on both sides of the piston is atmospheric, the pumping action wouldn't consume much power.

Another wild guess - what's done might depend on the engine. For example, removing the coupling rods wouldn't do much good on an engine with valve gear on the inside.

Dave

"Typically I can't find any photographic examples at present but I'm sure someone here will support or refute this."

Herewith image of LMS 6399 about to be towed from Derby to Crewe Wrks in March 1935 for conversion - devoid of coupling and connecting rods....added edit > "at least from the outside cylinders !"

Edited By Fowlers Fury on 29/12/2017 17:29:58

Canadian practice was something like:

Inside Stephensons - remove the straps, so that they get lost for preservation; (as per the E10-A in Morrisburg, ON)

Remove the connecting rods, keep the coupling rods on - but that means removing the return crank.

Both CPR and CNR stored locomotives for a bit in case of requirements. Here's a picture of a CPR locomotive stored:

**LINK**

(courtesy of Ray Kennedy's web pages)

Note the lack of coupling rods, the return crank still there, but the crank rod is not attached. I think, if you look at the front of the cab, the "thickness" of the running boards is due to the connecting rod being placed there.

You don't want the motion work, or the pistons moving about for a number of reasons; pumping of air, lack of lubrication (even if mechanical lubricator, the oil should go in with steam to keep it very liquid, and going to the right places)

Oh dear. None of you have heard of a 'snifting valve'. Interestingly LBSC almost never mentioned them and perhaps never include them or assumed people would sort that bit out for themselves. It is a valve to let air into the valve chests if there is no steam pressure in them. You also don't want the cylinders to produce a vacuum that might suck air backwards in from the exhaust because that would pull in ash from the smokebox.

By the way wrt vacuums in the boiler. If you are operating a model when you end the session you use some of the pressure to blow down then let it cool down but let off the last bit of steam with the blower and then leave it open. This provides a path for air to enter. With some locos if you don't the vacuum sucks in water through the pump but not all pumps will allow this so don't rely on it.

You will rarely find a snifting valve on a saturated engine because they are usually fitted with slide valves that fall off the valve faces so the pumping action of the pistons is completely negated. A superheated engine will have one on the smokebox behind the chimney (a la Mr Gresley), or on the main steam pipes (a la Mr Riddles) and as Baz points out it is to relieve the vacuum so that char isn't drawn from the smokebox into the valve chest and cylinders. On a cold engine it's academic since you need steam pressure to close the snifting valve(s). When coasting on a piston valve engine the practice is to set the cut off about 45% and about 10-20 psi on the steam chest to buffer the piston stroke end, keep the lubrication flowing and prevent the superheating elements from overheating.

When towing an engine any distance the practice was to disconnect the wheels from the motion, where depended on the particular motion fitted. Certainly many older engines had a displacement lubricator and obviously without steam no lubrication would reach the valve chests or cylinders. If your going to move an engine that has been static for some while 1/2 gallon of lub oil down the blastpipe is worthwhile and stops the worst of the groans.

When a full size boiler cools the water level drops and at the point where there is no pressure left the regulator valve is no longer tight on it's face which is enough to prevent a vacuum forming.

Hope this helps

Regards

Martin

My elder son took me to Shildon in 2011 to look at one of the two 2-8-0 locos which had only just been repatriated from Turkey. These are, I think, the engines mentioned above. This is the photo I took:

You can, just about, see that the cranks/connecting rods are missing. Indeed if you look closely, ie magnify the photo, you can see the bosses, one adjacent to the notice board and at the bottom, and another at 3.00 on the rear axle.

Incidently, my son, who is a member at Embsay & Bolton Abbey, on first seeing the loco, said "Where do you start on that?" Frankly, it was a mess!

Peter G. Shaw

Peter

You are wholly correct, this is one of the pair returned from Turkey. One has been sold on as a static exhibit in Israel. The other one has been bought by the Scottish Railway Preservation Society for restoration to running condition. Our one, despite it's outward condition, is actually in an amazingly good condition. The boiler which is inevitably the most expensive bit to restore is in a good condition with very little sign of wear. Tubes and superheaters will need replacing of course, but the firebox sides show little signs of grooving and the stays are apparently mostly intact. Most of the non ferrous fittings are there, the injectors which were missing have had replacements purchased, as have the motion brackets which are currently somewhat bent. Nobody would pretend that it is inexpensive to restore, but it will certainly be a lot less than ex Barry loco. Donations to assist would be gratefully received at SRPS Steam.

Regards

Martin

Coincidentally I recently watched on you.tube a video of UP #4014 4-8-8-4 'Big Boy' being towed hundreds of miles and noted that all the rods/valve gear were present/functional right up to the crosshead - but there were no piston-rods visible - perhaps they had been completely removed for the trip.
**LINK** see at around 5:38
DaveD

"....one of the two 2-8-0 locos which had only just been repatriated from Turkey."

Did it perhaps originate from the (quote) "Çamlık outdoor museum was inaugurated in 1991 just as steam was phased out from Turkey. It has one of the largest steam engines collection in Europe, most them joining the museum shortly after being retired from service." ?

'was lucky enough to visit there several years ago, a marvelous collection of non-working steam locos built around the world for running on Turkey's metals. The website doesn't really do it justice but maybe worth a look:-

http://www.trainsofturkey.com/pmwiki.php/RailwayMuseums/CamlikMuseum

A number of years ago I looked in on the preserved railway in South Dunedin, they had their little Dubs 040 tank shunting engine in the workshop, it had broken down while it was on a trip (Christchurch I think), and require towing home, the con rods were off, although I think it may have been the bearings in the con rods that were causing the problem. Lovely little engine.

Ian S C

Hi Fowler's Fury

The two 2-8-0s that returned from Turkey came from Silvas shed in the eastern part of the country, and as far as I am aware have never been at the Camlik museum.

Regards

Martin

Without steam it is not possible to reliably lubricate the cylinders on a steam engine as there is nothing to atomise the cylinder oil and carry it around the steam circuit. For this reason a 'dead' steam loco is generally towed without the connecting rods in place. You can remove the pistons but it is a lot more work and still leaves a bearing on the end of the Con rod with the risk of it running hot. Valves can be disconnected from the radius rod and the gear positioned so that any derived motion will not interfere. Bearings on the motion are generally wick fed so will continue feed oil without the need for steam and hence can generally be left in place.

They lined them up to tow them away and we schoolboys pinched the can of detonators the way school kids do. You knew which ones were to be towed because someone had oxy-acetylene cut through the piston rods.

Edited By Robin on 30/12/2017 23:23:45

Can’t you just slip it into neutral?

probably take the spark plugs out? (Sad but true).

I worked at the Stratford Loco traction sheds in the 80's, a number of times we had the flying Scotsman in to haul a Royal Train, it would be towed to the depot without the connecting rods fitted, which we would fit ready to pull the royal train then it would return to have the rods removed for towing back from where it came from.

Great memory's of riding the foot plate of the Scotsman around the shunting yard, along with many other loco's.