Correct Drift Cut-off for BR Standards

Recently been having a bit of a discussion over the correct drift cut-off position for BR Standard locos. The Black book has nothing to say on the subject. I'd like to see the diffinitive answer to this one. Already got lots of opinions based upon locos like GWR that have drift buttons, so on need for any further guesses, just the hard facts if anyone can provide them!

 

The Railway Executive "Instruction Book for Standard Steam Locomotives" says the following: -
Experience with new engines has indicated that coasting in long cut-offs leads to dirty valves, and the gear should not be moved any lower than 40% when coasting. There is no objection to coasting at normal running cut-offs, ie 20 to 25%.

I hope this helps you.

 

Thanks std tank: that looks like a book I should keep a lookout for.

 

That's an interesting statement and one worthy of further discussion. firstly, is there a distinction between drifting and coasting? I apply the former to running with a breath of steam on and the latter to running with the regulator firmly shut. A previous shedmaster on the NYMR (ex BR Midland) used to advocate coasting with the reg shut and the reverser wound back to 15-20% to get some compression in the cylinders; about 50 psi on the steam chest gauge.. Test carried out in conjunction with different grades of cylinder oil indicated that the very high cylinder temperatures occurred under these condition. After this, I started coasting with the reverser wound back until the stam chest needle just lifted off the stop, which as usually at around 25-30%. Nowadays, the preferred method is to drift (ie with a breath of steam) at about 45-50%. That accords with the 'D' on Stanier reversers. A lot of privately owned locos have instructions to this effect, as well. Only applicable to piston valve locos, though. Slide valve locos always in full gear.

 

The complete text about coasting from the Instruction Book.

 

Would dearly love to find a copy of the above mentioned book. saw a guy offering copies of it a few months ago on ebay, fingers crossed an original will turn up!

Chris