Why are Bulleid Pacifics more prone to slipping than other designs?

I was wondering the other day why it is that Bulleid Pacifics seem to have a reputation for being more 'light footed' and likely to slip than other locos.

Is this reputation justified?
And if so, why are they more likely to slip than other designs?

For example, I remember reading in a book by a fireman on the Somerset & Dorset (I think, I can't remember exactly) that crews were amazed by the sure footedness of other locos, like the GWR Hall class.
Whereas I was reading on another thread on here about the trouble some drivers have with 'Taw Valley' on wet days.

Thanks in advance!

 

I remember being amazed by watching 35028 slipping, light engine, as it left Didcot yard circa 1974/6. This after admiring the footplate and my attention being drawn to the rev counter!

Best regards

 

too much power being made available when opening the regulator ?

 

I'm not sure they're any worse than any other Pacific, since most have a high power to adhesive weight ratio and all can be very prone. The original Bulleids could additionally suffer from oil from the oil bath finding its way to the wheel treads, but the rebuilds didn't have an oil bath. Much also depends on the quality of the track, and shed yards are not renowned for being well laid. I can recall the 8F slipping quite violently in Bridgnorth yard, also light engine.

 

For starters there is a time lapse between opening the regulator, and steam being transmitted to the cylinders , so you could have 250 in the steam chest, and when this finds its way to the wheels, then yes the engine can slip, there is a method when you open the regulator , you give it a short pull, then close, wait for the wheels to move then another short burst of steam, this is because your sending full boiler pressure to the steam chest, and its easy to give it too much. Inexperienced drivers who have not had many turns on a Bulleid might not have the feel, so give it to much, it doesn't move, give it a bit more, and then its too much ,and the wheels pick up.

 

I think the reputation came from two sources. As had been said the originals were prone to leaking oil on the wheels and I understand that the pullout regulator handle could be a bit stiff so not easily controlled. The other problem is that with any locomotive with carrying wheels at either end of the driving wheels will be sensitive to uneven track with the possibility of transferring adhesive weight away from the driving wheels. The state of the track on the mainline platforms at Waterloo in steam days was pretty dire, see the sunken rail joint on the road adjacent to tge loco in the picture.
Today it’s down to the skill of the crew and I’ve never seen Clan Line get into any spectacular slip when pulling away but it only had three regular drivers when it’s on its home patch. One thing is certain there is nothing more impressive than travelling behind a MN getting away from Shalford with no trace of a slip and romping up Gomshall bank with 550 tons of heavy Pullmans behind the tender.

 

Didnt one Bullied take 20 minutes to get away from Brockenhurst as it could not get a grip?

 

Thanks everyone! Interesting to hear that they aren't, and to hear from @Johnb about where that reputation might have come from

 

I don't think they are any more prone to slipping than other pacific locos. (There was an interesting observation in, I think, DW Winkworth's book, where a careful observation of LMS Duchesses had been made from a particular station for a fortnight and the observer hadn't seen one "clean" getaway in that time, yet those locos don't suffer the same reputation.

A driver colleague of mine, well versed in driving all forms of the loco in the 1960s (rebuilt MN, original and rebuilt WC/BB) reckoned that they were fine provided you took care for the first wheel revolution or so on starting where, because trains tended to always stop at the same place at stations, you would invariably be starting on poor railhead. Go forward about one wheel revolution and then you could open them up.

Tom

 

They were the last Pacifics in 'Fleet' service in the UK so undoubtedly attracted a lot of attention in their last years.

 

Southampton Central platform one was such a case. The footbridge was a wonderful place to watch Bulleids slip and slide for a few feet.

 

This was the quote I was thinking of from Winkworth:

Were the Southern Pacifics so much worse than any other 4-6-2 then? There is no proved technical comparative basis for measurement of slipping that can be applied to the case, so one has to fall back on judgement (which so often is coupled with bias!) to provide an answer. The first British pacific - the GWR Great Bear - is reported to have been a bad 'slipper'. The Gresley designed 4-6-2s were by no means immune from this failing, nor were LMSR engines of that wheel arrangement, as reference to the columns of The Railway Magazine will show. [...] Two weeks noting of the start of a train from Rugby platform 1 (gradient of 1 in 365 in favour) produced no clean start, even on dry rail, from LMS Duchesses. Matters became so bad on the Eastern Region that an instruction was issued to drivers not to exceed 50% cut off on starting and, although considerable improvement was effected with the BR Britannia type, the LNER types did not benefit very much.

Probably the worst record of any was of a Duchess slipping for almost one hour (yes! hour) at Liverpool Lime Street trying to leave with a London train. The Southern engines used to slip, but the authorities took immediate action: for example, no. 7 platform at London Bridge was on a rising gradient and sharply curved and could cause trouble to London-bound trains which called there in the morning rush hour. Ramsgate-based light pacifics could sometimes have difficulty on starting and, if a shovel or two of sand from the sand box on the platform was of no avail, the following electric train was called forward to assist in the rear. The delay was seldom more than five minutes. When electric traction took over all traffic the stop was omitted!​

Tom

 

Thanks @Jamessquared for finding the quote! I hadn't realised other 'Pacifics' tended to slip quite so much

It must have been quite a day with that Dutchess at Liverpool Lime Street

I guesstguess from Winkworth's book on the Bulleid Pacifics? It sounds very good - I'll have to look at getting a copy

 

The only place I’ve ever seen them in real trouble was getting out from under the coaler at Nine Elms. Over the years the track had subsided and with the track covered in a mixture of oil and coal dust, I’ve seen them having to reverse back to the turntable and take a run at it.

 

Peter Smith discusses them quite a lot in "The Somerset and Dorset from the Footplate".

The unrebuilt locos had oil baths which sometimes leaked a little oil onto the rails.

Sent from my SM-A105FN using Tapatalk

 

First time I've ever seen that stated.

Incidentally GWR technical staff seem to have put their general relative freedom from slipping as being due to superior regulator design.

 

At Christchurch one Saturday in June 1950 (I thought it was Brockenhurst, but have just checked), the Hamworthy-Eastleigh goods included a tank wagon with filled either creosote or tar. The valve had worked loose and some of the stuff ended up on the track. Seven trains in all had problems starting as it was a hot day and the sticky mess melted, causing all seven trains to be badly delayed until sand was applied to the track. The worst affected train was the 7.20 Bournemouth West-Waterloo, which was hauled by a Bulleid and took 41 minutes to get going (Source: SR150, published by David & Charles)

 

Oil leaks from Bulleid loco oil baths would only get to rails when the loco was standing over pointwork. The oil bath is well within the frames, there must a be at least 10” gap between the wheel and oil bath each side.
However, oil does get to the wheel tyres from the excellent top feed axlebox lubrication system. Each driving axlebox has 4 feeds, 2 for the crown, 2 for the horns.
Oil overflowing the axlebox underkeep and running off the horns, collects in the pockets in the BFB wheels. When the loco is running slowly, the oil is tipped onto the wheel rim and tyre, and eventually the rail head.
At speed, this oil is thrown around by centrifugal force, some splats onto the boiler lagging, which soaks into the lagging! Creating fuel for fires.
Most spam cans in preservation have lightweight cladding on the underside of the boiler lagging to prevent oil soaking into lagging. BR may have done this too.