Garden Railway Forum

Hi all
One for the live steam enthusiasts.
As some will know, I'm presently working on constructing Glyn Valley Tramway rolling stock. I've decided to construct the locos in their later form, with their condensing apparatus removed. Apparently, they discovered it was affecting the performance of the locos by raising the temperature of the water in the tanks.

My question is, why would warming the tank water adversely affect performance? Wouldn't pre-heating water before it is put into the boiler improve the loco's efficiency? Or does it adversely affect the way the injectors work?

Rik

I THINK that the injector operation is affected by water temperature. So warmer water makes it harder to get the water into the boiler.

Injectors do not work with warm water, the colder the better. The cold water condenses the steam jet completely, allowing its velocity to be imparted to the water.

Some years ago a water tanker company thought they were being helpful when they delivered a tanker of warm water to a main-line steam rail tour. They didn't mention it was warm until it had been pumped in to the tender. Diesel to the rescue!

Many were the times on Linda or Blanche the injectors would give up around Rhiw Goch on a warm day. We used to switch to tender water, drain the saddle tank and re-fill with ice-cold Tanybwlch water when we got there.

ge_rik wrote: ↑Tue Dec 21, 2021 8:13 am My question is, why would warming the tank water adversely affect performance? Wouldn't pre-heating water before it is put into the boiler improve the loco's efficiency? Or does it adversely affect the way the injectors work?

As Greg and Tony indicated, injectors eventually stop working as the feed water gets warmer and it's vapour pressure increases. Water pumps can pump hot water, but need to be specially designed for the job.

To top it all off, diverting exhaust steam into the tanks also reduces the draught and therefore the steaming rate of the boiler, which reduces power output.

The usually given reason for fitting condensing gear to a tram loco was so it wouldn't frighten horses. One can only assume british horses scared easily, as the Americans didn't fit condensing gear to their steam trams and neither did the Australian steam tram systems.

Theoretically feeding the boiler with water heated by the exhaust increases overall thermal efficiency, but it requires more sophisticated equipment than that fitted to the GVT locos. Things like the ACFI feedwater heaters used in France, or the 25 Class condensing locos used in South Africa certainly increased thermal efficiency, but the extra maintenance usually cost more than was saved on the coal bill.

Regards,
Graeme

Thanks for the detailed and comprehensive responses, chaps. I knew there would be someone on the forum who could enlighten me (and others).

I read somewhere that they soon discovered the precautions they imposed on tram locos generally in the UK were quite unnecessary (ie no smoke, no steam, no visible connecting and coupling rods and a bell instead of a whistle). Horses were unperturbed by their clanking, chuffing road mates just as (it seems) they were in the rest of the world.

Rik