Tech Questions about Fairlies/Garratts

A couple of questions I've always wondered about theses Articulated Loco's.

Firstly the Fairlies - As is commonly known, the Cylinders, Motion and wheels sit on Bogies at either end (or the front in Taliesins case) rather than in a fixed frame like a conventional Loco, presumably this makes conventional steam pipes to/from the cylinders totally useless, what it used for the steam pipes that can supply such flexibility needed while coping with the steam pressure and heat while staying steam tight ?.

And a question which applies to both types - As your driving two seperate sets of driving wheels on both types, whats the standard practice if one unit is gripping and the other is slipping like mad, do you close the regulator and lose momentum or keep it open and hope the slipping unit finds adhesion, or does either type have a special trick for this situation ?.

 

I'm not an expert, but found this:

from Fairlie locomotive - Wikipedia, the free encyclopedia

Richard

 

The Fairlies currently have two different solutions in use for the main steam pipes.. The pipes themselves are in a U shape coming out from under the smokebox, backwards, then downwards before heading into the back of the steam chest between the valve spindles. Earl of Merioneth uses an older system of 3 solid steel pipes connected by swivelling joints at the corners of the U sections. Merddin Emrys and David Lloyd George employ modern flexible braided hoses for the downwards and forwards sections of the U, and a solid pipe for the top section. The flexible hoses remove the need for moving joints however they do tend to need replacing every 6 -8 months (obviously depending on usage of the loco). They are also have a bigger internal bore than the solid pipes which gives ME and DLG a lot more oomph than EofM. EofM will typically be on full regulator for most of the time with 12 cars whereas the other 2 are not. There are other reasons for this but the steam pipes certainly contribute.

The exhaust is via a pipe from the top of the steam chest with a spherical joint on bottom end. This then sits inside what is known as the inca temple inside the smoke box. It is a large tapered box with the blast nozzle on top. The exhaust ball joint is sealed with a PTFE ring so if you see steam coming from under the front of a double engine it is typically because this has worn and the the joint needs nipping up. The main steam pipes are rarely a source of trouble these days.

Garratts being inferior machines have telescopic as well as spherical joints to worry about. I'm sure someone on here has managed to look at one long enough to tell you all about them. Sadly they hurt my eyes to much.

As for the second question Fairlies have a separate regulator for each bogie. So if one slips you can reduce power to it independently of the other one. On a Garratt there is only one regulator so I'm afraid you have to reduce power to everything. Waiting for it to magically grip once it is slipping will get you nowhere apart from maybe back down the hill you came up.

 

Cheers for that info Guys, probably not a suprising the pipes on Fairlies need changing after several months considering what they have to go through.

Didn't realise either end of a Fairlie could be driven independantly, is controlling both units at the same time a two hand job then or is there some device that lets you open/close both regulators at once ?.

 

The regulators are next to each other so can be operated by one hand. See pic of DLG below.

 

You can quite easily work them with one hand and this is the preferred practice to avoid confusion. The same applied to the fireman's control valves when they were on oil. A good ear is required to balance the regulators and make sure both ends are sharing the work. In case you were wondering there is a one common reverser for both ends.

James Spooner was fitted with a central wheel that could be used to operate both leavers at the same time. The regulators could still be controlled independently if necessary. This photo gives a good view of it File:JTJ.S.jpg - Festipedia

The braided hoses often fail where at the ends where the metal cap with the fitting attaches. They usually they give a few signs they are on the way out but they have been known to go with a bang while in service.

 

I do get entertained by the idea that Garratt's are inferior to Fairlies. And how many of each were built in the 20th century?

 

Boston Lodge built three new Fairlies and no Garratts in the 20th Century.

But I defy anyone who's ridden on the footplate of an NG/G16 up the 1 in 40 from Beddgelert to Rhyd Ddu to describe it as inferior to anything.

 

I have and it's all 15mph or less for the most part up there and you are on an engine that was built to do that sort of thing anyway. A little underwhelming I thought.

Now Linda or Blanche running late up the FR with 8 coaches of fat Americans in tow. That is a real white knuckle ride.

 

I love the smell of casual racism in the morning...

 

Having fired and driven No. 87 up there a couple of times, I have to say "underwhelming" is the extreme opposite of what I experienced.

Having also driven both Linda and Blanche, I likened them to "the Mad Mouse on Speed." Equally exhilarating. Thought the comment about fat Americans was unnecessary.

 

Because the NG16s have a very much larger boiler I would expect that they would be the more powerful engine ... but ... the exhaust on these machines is very much less sharp than the Fairlies so I do wonder just how effectively they're using the additional steam at the front end.

Regards

 

What's the firing technique like on a Fairlie? I'm assuming there is one central firebox, but does the firebed tend to get pulled apart by contrary blast? Or does the unit effectively consist of two separate boilers in one shell?
Thanks,
Dan

 

Part of why the exhaust of a garratt can sound soft, is the long exhaust pipe from the rear unit to the chimney. Fairlies have a short, but convoluted exhaust pipe cylingers to blast pipe. (As explained earlier in the thread.)

Remember that noise from the chimney top is waste energy. Listen to a loco with a modern front end and good gas flow and it will be comparitively quiet. Think of 60163 with a kylchap exhaust or 70013 with a conventional blast pipe.

When worked hard, modern garratts (and that includes an NGG16) the exhaust beats from the front and rear units wander in and out of phase just like double headed locos. I you can track them down, some of the recordings of GMA's around Petermaritzberg in the 1970's are a wonderful example of this effect.

Just to put a (very old) myth to rest. Years ago it was said that the front and rear units of a garratt became syncronised. As they were separate engine units with a common boiler why would that occur? I'm certain the more technical members on here can come up with quite a list why they wouldn't syncronsie. The explanation is that the early garratts didn't have streamlined steam passages, so the exhaust noise of the rear unit was muffled and not heard over the noise from the front unit.

Cheers, Neil

 

Perhaps coincidence, more good maintenance and careful driving with minimal slipping!
In those cases both engine units have gone through tyre turning at the same time and have not worn unevenly, normally due to slipping. I've just looked the wheel tolerances for SAR up in the Dusty Durrant book on Garratts. There could be up to 0.031 inch difference between wheel diameters on the same engine unit, but up to an inch between the average wheel diameter between two units.
OK, most of the Garratts that I experienced in the late 1970's or early 1980's (SA or Zimbabwe) were run down and waiting for the diesels to take over.

Cheers, Neil

 

In my limited expierience, both Garratt and Fairlie power units syncronise fairly quickly (maybe 1/4 mile or so) when under heavy load. I have no idea why this may be the case, but they always seem to

 

A Fairlie has two separate fireboxes, in one long double-ended boiler (ie the water-space is continuous). I believe that the original fairlie had one firebox and didn't work effectively because of the contrary blast. Hence the two fireboxes ever since.

Steve B

 

I concur. I used to drive both types at the FR and WHR. When leaving Penrhyn on an Up train, for example, a Fairlie would often be out-of-sync as the train pulled away, but by the other side of the road crossing both exhausts would synchronise and remain "locked" together. Much the same would happen with an NGG16 and there would never be any phasing of the exhausts as described.

Why it happens is a mystery to many more learned than myself, but I am told the effect also occurs when a number of out-of-sync grandfather clocks are left in room but after a while they will all be ticking together.