LMS Patriot Project Updates

That's the set up on 35028.

Edit.
Pipped at the post above!

 

I think (but am not certain) that the rules have been tightened since then and the air pump now needs to be on the loco.

 

I would expect it has to be fitted in the vertical plane also, very difficult to hide....
Also, a shame that they are all the reciprocating type !

 

So if vac only you would be limited to WCR, SRPS and Vintage Trains stock as things stand at the moment.

Dave

 

Last Friday the outer firebox back plate was completed ready to send to Crewe. Only the throat plate left to do and then it's time to assemble the firebox!

 

A work of art, the throatplate even more so.
Tucked inside the smoke deflector looks like the best place for an 'air-pump
on this one unfortunately.
Is the braking performance of Air -braked trains( of heritage rolling) stock significantly better than Vac braked ? If so is it likely that regulators will in future decline to accept Vac...?

 

Yes air brakes have more braking power than vacuum brakes, but on steam they have a bit of a tendency to break down, more so than vac brakes.

 

The only other place I can see, is up against the Firemans side cab front and disguise it with a dummy AWS box, which they carried of course, I know an air pump is a big lump, around 370kg. but it may hide the majority of it ? but between the frames would be the ideal location...

 

Sadly this is an incorrect myth. As a for instance, take a dual brake mark 1 where the brake shaft is worked by either air or vacuum cylinders. Given the size of the cylinders, the arm of the relevant brake lever and the effective pressure of the medium applied (air or vacuum) a fairly simple calculation will demonstrate that the difference is around just over 1% in favour of air. That is for vacuum working at the 21"Hg of the average vacuum system. However if you are using the superior Great Western value of 25"HG there is a noticable increase in brake power over and above that resulting from air. Where air does have an advantage is in the propogation time for complete applications at the rear of the train but this is a very small number of seconds difference where vacuum fitted vehicles are equipped with Direct Admission valves, and air only really becomes a necessity at speeds approaching 100mph and above, certainly there is no significant demonstrable difference at the normal speeds experienced with steam operation.

Whilst people keep peddling this myth without any facts to back up their assertions, it can only add to the strength of others similarly ill informed who wish to pursue the demise of the vacuum brake. The path to reliable and more effective brakes on heritage stock is not the less reliable air brake, all you have to do is to up the vacuum to the GWR's 25 inches !

Regards
Bob

 

Scrap that air pump idea now...

 

Oh - Light blue touch paper and retire. Seriously cant fault your logic although you need 25in to cope with the leaky wiper seals on GW stock. Rolling rings seem to seal better. I would not object to 25in as a standard as it would save me pulling all 16 strings when there is a loco swap at Bridgnorth when a 21in loco comes on in place of a GWR one

 

Presumably air brakes COULD operate at a higher pressure that vacuum and so be stronger, maybe this is where the myth comes from?
Clearly a vacuum is physically limited and the GWR's 25inHg is about the practical limit.
What pressure do air brakes normally run at?
I once had a very tedious email set of email correspondence in a professional capacity with a qualified engineer who called himself an expert, who was most indignant about my insistence that his calculation showing he had a 5bar vacuum in his system could not possibly be correct... Not sure he ever did believe me.

 

On 14-6-2014 after we'd been round the Cumbrian Coast behind the 8F and they were changing back to electric traction at Carnforth for the run back to London, there was some delay in getting the coaches switched from vacuum to air. I understood one of the crew to say that they could stay on vacuum if they had to but it was better to run with air if possible. I think he gave a reason but I've forgotten what it was.

Isn't it quicker to release the brakes with dual-pipe air than with vacuum?

 

Air brakes operate in the region of 70 to 75 psi. If you want bar you convert it yourself

 

I very strongly suspect you'll find the limiting factor is that if you increase the brake power the wheels will just lock up and you'll get flats. My understanding is that because air brakes run at higher pressure the cylinders are much smaller, and this was a key reason why freight stock migrated to air brakes. If the air pressure was increased the cylinders could be smaller yet.

 

Interesting...

 

75psi is about 5 bar g.
While 25inHg of vacuum is about -0.85 bar g.
So air has the potential to deliver a much bigger force for the same size of cylinder or, as someone has already said, have much smaller cylinders for the same force.
Presumably that is why some railways preferred it.
Plus the leaks are in the right direction...

 

Depends how you look at it. With a vacuum the tendency is to draw parts such as hose couplings together so helping to seal the system. Positive pressure forces them apart, encouraging leakage.

Vacuum braked vehicles have been known to maintain their vacuum even after standing for several weeks. Not with air, though!

 

True enough!
I'm not very familiar with railway braking systems, as is probably very apparent, but in other applications the problem with vacuum is that leaks draw in water, gunge, etc. Water being particularly dangerous if you get sudden expansion/contraction or of course if hot enough to boil!
The other advantage of air systems is that tubes and pipes are of course stronger against positive pressure difference from inside to outside.