Member postings for Dick Allan

I am not familiar with the Tich layout but I did once experience similar problems and eventually found they were due to an interaction between the blower and the top water gauge fitting. The latter had been fitted to a turret outlet and one could observe the water level changing when the blower was turned on and off. I imagine this might occur if the top water gauge fitting was closely adjacent to the source of blower steam, although the dynamics of the situation are difficult to understand. As a builder of small G3 locos I often fit the water gauge to an elbow on top of the boiler as this gives room for a longer glass. I have never had any problems with this arrangement.

Dick

Hi Eric,

Ayesha, one of LBSC's most famous engines, is in the care of the 2 1/2" Association and right now is on their stand at Sandown Park

Dick

The Southern Federation of Model Engineers has issued a supplement to its leaflet on boiler testing to cover the testing of liquid gas tanks. It makes it clear that the code does not apply to commercial, non-refillable canisters of gas but makes no mention of commercial re-fillable tanks such as are supplied with test certificates by companies such as Bix and Cotswold/Heritage. Can anyone throw light upon the the position regarding these?

I am delighted to have given so much amusement to you all in worling out what the back end of Derwent's main frames should look like! Martin Kyte is right, I should have given dimensions for the buffer beam (actually the drag beam) and these are 0.842" from the top line of the frame to the top of the beam and 0.470" from the bottom of the horns to the bottom of the beam. That done the exact shape of the curves is not very critical - for my own Derwent I set them out by eye! Neverthe less I am full of admiration for the display of mathematical wizardry.

While I am at it, several of you noticed the errors in positioning the water tender axle boxes (Fig 25, ME4469). Of course it is blindingly obvious the something is wrong and, no, it is not an optical illusion as one contributor wondered! This is what happened. Using Draftsight (CAD programme) when drawing in multiple objects of the same design one designs only the first and then ' copy/paste as a block/ paste as a block etc for as many as required, placing them only roughly in place. The objects are then moved into acurate positions. I did this for the pair on the righthand side of the drawing when an interruption took me away and I forgot to finish the job. Anybody building the model will find it obvious where the axle boxes have to go as they have to fit into the limited spaces in the under frame. I was surprised that the plan was redrawn for ME without this being noticed!

I will be pleased to meet any of you who may be attending the Sandown Park exhibition where I will be exhibiting a gauge 3 model of the Crampton 'Liverpool'.

Dick Allan

Hi Mick

thanks for that. Do you happen to know if 70%/30% butane propane mixed gas is covered by the GIMRA rule? The canisters in the shops are the same for this mix as for pure butane

Dick

Thanks JasonB for that. Looks like 285PSI is right for 70/30 mixed gas. I don't think there is any significant risk of filling with the wrong gas mix as 70/30 is almost universal in the shops and I believe I'm right in saying that the propane proportion decreases during use.

Hi Terry

mixed gas canisters from B&Q which are 70%butane and 30% propane

Hi Michael

I quite agree and it is simple to do the calculations. The problem seems to be that 1. people are not recognising the much lower vapour pressures with butane or mixed gases,2. some seem to think there is a heating problem but in practice the problem is gas tank cooling during evaporation,3.When not in use obviously there is no fire and the only way overheating can occur is by the tank being left in the sunlight or otherwise exposed to temperatures of 50C or above. This of course is precisely the same as for B&Q canisters (the cans have a warning to this effect), also the cans are more likely to be dropped or thrown about than proper installations in a loco and more likely to be left in the sun as the loco tanks are generally covered inside cabs or tenders. An overpressure switch is an interesting idea but would be a complication and expense and is the problem was exposure to direct sun it could make things worse by removing the evaporative cooling whilst leaving the heat source!

Dick

Thanks for all the replies. I'm still not entirely clear about this. There must, for instance, be a capacity limit for the 'rules' or one could not fill a cigarette lighter! Also the difference between propane and butane70/propane30 mixed gas is very large - one contributor to a previous forum on this subject said at 50C the latter would reach a pressure of approx 60 PSI. At more likely working conditions it is close to 40 PSI. In use, everyone knows that the real problem is the gas tank getting too cold! One recent article on a boat installation suggested using a solid copper shunt between the boiler and the gas tank to solve this problem.

Looking at the cylinders in my local plumber's merchant it is obvious that the standards applying to propane and MAPP cylinders are totally diferent from those for butane and mixed gas cylinders. Also I,ve seen a label on a gas tank for a G1 loco saying ' tested to 160PSI' so it looks as if some dfiferent rules were being applied.

Dick

Can anyone advise me on the construction and test requirements for gas cylinders for firing models. I have heard mention of 300 psi but I doubt if the tin cans in B & Q would survive that, Also does GIMRA have a lower ? 160 psi requirement?

Dick Allan

The problems with the main frames were sorted several weeks ago and they are available from SCISS Ltd. A new frame drawing and a list of other minor corrections were published in ME 4423. I will be happy to help with any problems builders might come across so please be in touch [email protected]

Dick Allan