Push Pull Control Systems

I am familiar with the GWR mechanical system, but what other push pull systems were used in the UK & abroad with steam locos & how did they work/what were their limitations.

I understand that certainly in Europe some suburban services of up to six or so vehicles were operated with tender as well as tank locos.

 

Since nobody else has had a stab at this, I'll add what little I know.

The SR inherited two systems from its constituent companies; the LBSCR had a compressed air system and the LSWR had a truly Heath Robinson arrangement of cables and pulleys devised in the Drummond era. In the early days the two systems were maintained in parallel, but some potentially dangerous incidents around 1930 on the Bournemouth West - Brockenhurst services led to the LSWR system being scrapped and (after a short period where transferred LBSC locos covered services) some LSWR classes being converted to the air system. In later BR years some SECR 0-4-4T classes were also converted to replace withdrawn LBSC tank engines.

Various members of the the 0415 (Adams Radial), T1, O2 and M7 classes were at times fitted with the LSWR system, but apparently only the O2 and M7 were popular with crews for pull-push working (the SR called it this rather than push-pull), and when the conversion to the LBSC system was made none of the 0415s or T1s were fitted.

The compressed air system can generally be spotted in photos by the presence of Westinghouse pumps on locos which wouldn't otherwise carry them (anything non-Brighton that isn't on the Isle of Wight), and a small vertical cylinder in front of the side tank, with the piston rod leading up to a crank actuating a long shaft leading back to the cab. There's often also another small air reservoir on top of the tank, which was the reserve cylinder to close the regulator if the main air system failed, and an array of air pipes under the buffer beam to put an early dual-fitted diesel to shame. Inside the cab another crank arrangement drove the regulator, with a pin that could be removed for normal working. It was often left out anyway by crews, with the fireman doing all the driving on the loco and the driver handling the brakes, though this was officially strongly deprecated. It seems to me that the braking would have worked better on ex-LBSC Westinghouse fitted stock, since the high pressure air being piped to the drivers compartment would have allowed a proper brake valve to be fitted, as opposed to the usual rules with vacuum where the fireman took the brakes off with the ejector and the driver had to apply them against the ejector from the other end of the train...

I've never been able to find any details of exactly how the regulator functioned, but presumably the driver's control was a variable pressure regulator and the cylinder on the loco had porting such that certain pressures moved the piston certain distances. Classes I have seen recorded as fitted with the LBSC system include (LBSC) A1x, D1, D3, (SECR) R1, H, (LSWR) O2, M7. Preserved locos that once had the system include 30053 (to the end of her BR days), W24 (when first shipped to the Isle of Wight), and 263 (at the end of BR career), but as far as I know there are no engines currently fitted.

I believe the NER also had a compressed air push pull system, but don't hold me to that.

The LMS had a vacuum operated system fitted to a variety of 2-6-2T classes (at least). I don't know much about it, but it has a couple of pancake vacuum cylinders next to the external steam pipes, operating separate regulators in series with the normal one. I can see this system being quite handy, because the fireman would have the main regulator to control slipping (and make notching up easier) while the driver can shut off completely when required using the auxiliary regulators and open them wider for more power. There are tales of inspectors spotting SR crews working 'pin out' when a driver had to apply the brakes in a hurry leaving a station and the loco kept pushing for a few seconds; with the LMS system that wouldn't be so liable to happen.

In short, the compressed air systems were probably the best in terms of maintaining control over a long train (and air is a much better control medium than vacuum), but the LMS system with inline regulators probably had some significant advantages over the ex LBSC one in terms of actually driving the loco with it.

 

In the weird and probably not so wonderful stakes the Taff Vale had a system with what appears to be a series of cranks on the cab roof and wires or thin rods leading to another assemblage on the sides of the chimney. Unfortunately I can't find a pd or cc photo on line.

 

To add a bit to @8126's description above about the system used by the SR constituents: The SECR also used two different systems of Motor Train working (as it was generally known).

The P class locos had a system of "pulleys, wires and rods" (to quote Bradley), and were generally worked sandwiched between two bogie carriages, or four six wheelers. On the Bluebell, 323 still has a large hole in the centre of its regulator rod which I assume is a legacy of the control linkage for the system, but visible clues to how it may have been arranged are not otherwise especially clear. It's possible the other P class locos preserved (27 and 178 on the Bluebell and 753 on the KESR) may show evidence, but I haven't looked closely.

The SECR also used a compressed air system on some locos, which was described as being very effective in use; I assume it's use was limited to former LCDR locos, that line being air braked.

The Brighton system (air controlled) was generally considered satisfactory in use. Care was required coupling however; there was a notable accident at Littlehampton in 1920 when a non-motor equipped loco was coupled incorrectly to a motor coach, with the result that the motor train control pipe on the carriage was connected to the locomotive brake pipe, resulting in the train having no brakes and thereby crashing through the buffers onto the street beyond, fortunately without fatalities. The accident report makes interesting reading: http://www.railwaysarchive.co.uk/documents/MoT_Littlehampton1920.pdf

The LSWR system, apart from its other faults, also restricted forward view and was sometimes only fitted to the rear of the loco, restricting use to carriages at one end only. The preserved NRM M7 No. 245 was thus fitted some time round about the end of World War 1. When the LBSCR compressed air system was adopted on some M7s, it could only be fitted to the long-frame variants which had space for the additional air tank behind and underneath the front buffer beam; No. 30053 is of this form. There were at least two examples in which pairs of long and short frame M7s entered the works in BR days with one good loco being made out of two (with the remaining parts nominally scrapped), but in which the loco that emerged was the long frame loco carrying the short frame number.

Tom

 

Hello, TVR push and Pull loco:

1. 
   
2. 
   
3. 
   
4. http://gwr813.org/GWR1301.htm

 

For a more French take on things, I've just remembered the mighty Nord/SNCF 2-141TC 2-8-2T class, used on freight work and the Paris Gare du Nord suburban services. They had a variant on the Nord 'Super Pacific' narrow firebox boiler, so think something halfway between a GWR 4700 and a 9F (only with more tractive effort than either) in tank engine form running fast push pull suburban services up to 1970. I don't know anything about the system employed, although they have quite obvious auto couplers, but I'd guess compressed air again, given the use of the Westinghouse brake on the continent.

Here they are in action in 1969. Wonderful beasts. There's one preserved, but it's stored outside and I've not seen anything to suggest it's ever run in preservation.

 

As an associated query, at the LMSCA we had a question asked about LMS Push Pull vehicles (or Pull Push in LMS parlance) - they were fitted with a whistle - how did it work?

Dave

 

I like the piece of Meccano operating the 'mechanical lubricator?' on top of the cylinders!

 

That's the valve gear!
What struck me was the almost complete lack of smoke.

 

Hello,
Another Taff Vale example:

https://www.flickr.com/photos/25830408@N08/24397269955/in/dateposted-public/



nick

 

Good stuff. With the discussion we had elsewhere about GW identification showing through BR paint, do I see a Taff Vale crest showing through GW paint?

 

The TVR crest would have been where the GWR number plate is in this photo. The mark in the middle of the tank is perhaps scarring where a number plate used to be?

 

Hello,
Yes this was where the number plate was:
See

https://www.flickr.com/photos/25830408@N08/24209826582/in/pool-2951766@N22/



Nick

 

Nice works photo of large wheeled passenger 0-6-2T U1 no 197 wrongly captioned as M1 no 169

 

He

Hello,
Thanks for the correction.....tend to be a bit word/ number blind!


Nick

 

If you receive bonuses for both fuel economy and time recovery to say nothing about a very high level of training an outside observer should witness the results of this. Locomotives that deliver a high power to weight ratio are very welcome if you are running your trains with such a remuneration system in place.

 

As the Wikipedia entry says, this was "Cossart" valve gear operating piston drop valves. In this particular layout the valve actuating rods were arranged to operate in the opposite phase to the connecting rods and weighted to be of equivalent mass. This took care of reciprocating balance leaving the weights in the driving wheels to deal with rotating balance only.

Marc de Caso schemed this arrangement. How fortunate France was to have two people of the calibre of Chapelon and de Caso in their prime simultaneously!

PH

 

This is also the reason for the 'meccano' noted by @Nick Gough, they're lightening holes to get as much weight out of that rod as possible, because every bit of reciprocating mass in that rod needs to be matched by mass in the rod attached to the return crank (which is going the other way). The balancing rod off the return crank already needs to be >2x heavier than the reciprocating mass of the crosshead and connecting rod, because of its short throw, so it's quite heavy enough already. It's an elegant arrangement, but everything has a trade-off.

 

What a wonderful change to have a thread where I have genuinely learned something interesting, as opposed to how easy it is to set up a Fudbook page / dream of reopening a railway and how good railway enthusiasts are at disagreeing with each other!

 

Swanage hope to restore a two coach 'push-pull' set to run with 30053, 1959 conversions of Maunsell origins. Not sure if they will restore the driving equipment at moment, someone said it might not be able to under health and safety but I can't see that being an issue if they allow the GWR mechanical system to work...

Swanage's Maunsell and the LCDR four-wheeled set on the Isle of Wight I think are they only Southern Region 'Push-Pull' stock left.