Dog Star
Western Thunderer
No.... because I cannot clarify the vacuum pump on this loco (or the 1361 class) for myself. I shall try to explain in a day or so.
simond
Western Thunderer
Chris, Graham,
thanks both.
The “pot” on the most recent photos is in the same place as the curiously shaped pot on Dave’s earlier post, but is a different shape. I’m going to have a look through my books and see if I can find out more. Might get a chance tomorrow evening.
atb
Simon
thanks both.
The “pot” on the most recent photos is in the same place as the curiously shaped pot on Dave’s earlier post, but is a different shape. I’m going to have a look through my books and see if I can find out more. Might get a chance tomorrow evening.
atb
Simon
Dog Star
Western Thunderer
Simon,
This link... GWR locomotive lubrication in the 1930's | Model Engineering Clearing House ... includes a decent photo of a pepper pot, also known as a vacuum relief valve; there is going to be one of those in the vacuum system somewhere. Until I started looking for the pepper pot on a 1366 class I believed that the valve was screwed into the top of the vacuum pump.... I cannot see it in any photos of either 1361 or 1366 class locos.
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Rgds, Graham
This link... GWR locomotive lubrication in the 1930's | Model Engineering Clearing House ... includes a decent photo of a pepper pot, also known as a vacuum relief valve; there is going to be one of those in the vacuum system somewhere. Until I started looking for the pepper pot on a 1366 class I believed that the valve was screwed into the top of the vacuum pump.... I cannot see it in any photos of either 1361 or 1366 class locos.
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Rgds, Graham
James Spooner
Western Thunderer
Hi Simon,
Just had a quick look on Google and came across the attached, which, towards the bottom, has a sectioned drawing of a GW vacuum pump. One of the three pots on top is a vacuum relief valve.
cheers
Nigel
Just had a quick look on Google and came across the attached, which, towards the bottom, has a sectioned drawing of a GW vacuum pump. One of the three pots on top is a vacuum relief valve.
cheers
Nigel
Pencarrow
Western Thunderer
I should have added that both photo snips are preservation era.
Many thanks for that - it is a brilliant resource (particularly GWR Mechanical Institute Papers - K&ESR Virtual Mutual Improvement Class) The papers listed there by some real experts of their day are a real goldmine and the provide a real insight into what was really going on - and not only on the GW. I cannot understand how I missed it until now!
simond
Western Thunderer
Thanks Graham,
my understanding of that vacuum relief valve is that it is in the steam circuit to prevent the ingress of cinders etc through the blastpipe by the avoidance of a vacuum in the live steam supply when the regulator is closed. I'd have called it a snifting valve, but I rather thought they were much bigger - perhaps this one is used on the ejector supply? It also looks rather like the valves that are fitted fore and aft on all standard GW cylinder end plates, which I took to be overpressure relief valves - if that is the case, it will make the engine rather freer running with regulator closed.
Putting one of these into the vacuum pipework would break the vacuum, as it allows air in through the holes in the cover, and the pressure differential across the valve head (which is hidden) pulls the valve open against the spring. This would not be helpful in a vacuum system and I don't think it belongs on the vac pump.
We want something like this - the "bicycle dynamo" which is definitely a lubricator.
cropped from Dave's photo
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Dave Holt
Western Thunderer
Simon.
Loco vacuum brake systems are provided with a spring loaded relief valve to prevent the system vacuum exceeding the specified maximum - 25 inches Hg for the Western and 21 inches for everyone else. The vacuum relief valve generally has a cover perforated by small holes to prevent debris being sucked into the system when the valve opens - hence the slang term "pepper-pot".
Because the vacuum pump still created a vacuum when the brakes were applied, a device called the retaining valve isolated the pump from the train pipe but continued yo evacuate the reservoir. It was then important that the relief valve prevented the reservoir vacuum exceeding the maximum, otherwise it would be impossible to release the brakes. According the the Handbook for Steam Locomotive Enginemen, the relief valve on the pump was set to 23 inches.
Dave.
Loco vacuum brake systems are provided with a spring loaded relief valve to prevent the system vacuum exceeding the specified maximum - 25 inches Hg for the Western and 21 inches for everyone else. The vacuum relief valve generally has a cover perforated by small holes to prevent debris being sucked into the system when the valve opens - hence the slang term "pepper-pot".
Because the vacuum pump still created a vacuum when the brakes were applied, a device called the retaining valve isolated the pump from the train pipe but continued yo evacuate the reservoir. It was then important that the relief valve prevented the reservoir vacuum exceeding the maximum, otherwise it would be impossible to release the brakes. According the the Handbook for Steam Locomotive Enginemen, the relief valve on the pump was set to 23 inches.
Dave.
simond
Western Thunderer
Thanks Dave, that makes sense, so not so much a relief, but limiting, valve. I was aware of the retaining valve.
simond
Western Thunderer
Interestingly, the drawings that Rob scanned at the NRM suggest no oil pot, and the brass casting that Chris had purchased (which I did not use because it was faulty) also had two valve boxes, and an outlet flange, and no oil pot.
In this tiny clip, you can see the '4" x 20" air pump' (well, you can't pump a vacuum!) with its two valve cover plates, and the bracket from the hanging bar down to the pump. It is possible that the circular dotted line directly below the "L" of "Length of frames" is somehow connected to the pump, but it is far from clear. It seems to me that it is more-or-less coincidental with the boss on which the oil pot is mounted in Dave's photo, which suggests that it should be there, so I'll have a go. There are also photos of pumps with remote oil feeds and that too could be connected to the same boss.
Of course, the pump is on the driver's side, and the side views are of the fireman's, so that does not help.
In this tiny clip, you can see the '4" x 20" air pump' (well, you can't pump a vacuum!) with its two valve cover plates, and the bracket from the hanging bar down to the pump. It is possible that the circular dotted line directly below the "L" of "Length of frames" is somehow connected to the pump, but it is far from clear. It seems to me that it is more-or-less coincidental with the boss on which the oil pot is mounted in Dave's photo, which suggests that it should be there, so I'll have a go. There are also photos of pumps with remote oil feeds and that too could be connected to the same boss.
Of course, the pump is on the driver's side, and the side views are of the fireman's, so that does not help.
simond
Western Thunderer
thanks Nigel, it is labelled "3" & "vacuum adjuster valve" in the diagram and it does look like the dismantled valve in Graham's photo - I note that this pump has a remote oil feed.
The said vacuum relief / limiting / adjuster valve does not appear in the NRM drawing, nor, I think, in Dave's photo.
Looks like I was wrong about not having them on the vacuum system!
atb
Simon
Dog Star
Western Thunderer
In case other WT-ers are thinking of enhancing the vacuum pump on their GW locos, my 'net wanderings have, I think, showed me that there might be more than one design of pump... and that is without different "lengths" of pump because a pump from say a Saint would not be used for a Star or a Castle (think piston stroke...). I have found some pump images which I shall reference before the week end.
simond
Western Thunderer
thanks Graham, I have found some faint dotted lines and nothing more. The pump stroke must, of course match the piston stroke, and, as far as I have checked the locos with ejectors didn’t have pumps, and vice versa, it would be useful to confirm that observation.
Happily, many locos have the pump up tight under the footplate so many of the details are hidden!
Pencarrow
Western Thunderer
...but of course the blessed 1366 has to be the problem child!
Dave Holt
Western Thunderer
Simon.
Looks like you're getting there. I would suggest that the "rib" along the top of the body (actually a hollow chamber connecting the end valves) is more rectangular in section rather than semi-cylindrical, as drawn. If you look at the photo, the intersection between the rib and the end valve body and lubricator feed is an almost vertical straight line.
The vacuum pump served to maintain the vacuum and reduce steam consumption whilst in motion. All GWR locos had a brake ejector to create and maintain vacuum whilst stationary, whether or not there was a visible external ejector and/or exhaust steam pipe.
Dave.
Looks like you're getting there. I would suggest that the "rib" along the top of the body (actually a hollow chamber connecting the end valves) is more rectangular in section rather than semi-cylindrical, as drawn. If you look at the photo, the intersection between the rib and the end valve body and lubricator feed is an almost vertical straight line.
The vacuum pump served to maintain the vacuum and reduce steam consumption whilst in motion. All GWR locos had a brake ejector to create and maintain vacuum whilst stationary, whether or not there was a visible external ejector and/or exhaust steam pipe.
Dave.
simond
Western Thunderer
Thanks Dave,
I should have said “large ejector”. Do the big locos (Halks, Castles, Counties, Kings, etc.) have vac pumps?
I've not seen evidence of it, but of course that’s not the same as seeing evidence of not…
I started with a round rib for the passage, and then realised it’s more likely flat sided with a radiused top, but it’s all very small. What can be modelled in CAD and what will print are not always the same. And I haven’t got a drawing, so it is all an artistic impression anyway (oh dear, the Russian judge has marked him down again…) I’ve not printed it yet, so there is still time to modify it.
Ta
Simon
I should have said “large ejector”. Do the big locos (Halks, Castles, Counties, Kings, etc.) have vac pumps?
I've not seen evidence of it, but of course that’s not the same as seeing evidence of not…
I started with a round rib for the passage, and then realised it’s more likely flat sided with a radiused top, but it’s all very small. What can be modelled in CAD and what will print are not always the same. And I haven’t got a drawing, so it is all an artistic impression anyway (oh dear, the Russian judge has marked him down again…) I’ve not printed it yet, so there is still time to modify it.
Ta
Simon
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Lyndhurstman
Western Thunderer
A remove makes my memory strained, but some GWR engines had both ejectors (large/small) and pumps. The pump was on the drivers side, I think between the first and middle axles. Linked to the crosshead, I seem to recall. It would take the place of the ejector once the loco was up and running. Vacuum (said in my head with an associated Midlands accent - 'Vacum' - as my footplate trainer worked out of Birmingham) could be maintained by the small ejector.
Origins of the Great Western Vacuum Brake
Introduction In the development of the locomotive engine the initial challenge was to make the machine go. Stopping was less of a pri...
janfordsworld.blogspot.com
Cheers
Jan