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It seems local uses vacuum, but the engine rented uses pressure, told not permitted to use simple pnewvac can any one explain why?
Rail cars or carrages. Method of braking.
- Thread starter ericmark
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Maybe spell check and grammar , can’t make head nor tale of your question.
Vacuum can be produced using a venturi with minimal moving parts. Also far less condensation in the pipes of a vacuum system.
Being lazy so took this text from Wikipedia
Driver's brake control on a combined control and ejector. The ejector steam nozzles, large and small, are beneath the hexagonal brass plugs on the left.
Vacuum brakes were initially favoured over air brakes because of the ease of producing the vacuum. A vacuum ejector was a simpler and reliable device, compared to the reciprocating pump.[3]
Typically two ejectors are fitted, large and small. The large ejector is used to 'blow off' the brakes, by producing the vacuum, and is then shut off. The small ejector is left running continuously in order to maintain it.[4] The Gresham & Craven 'Dreadnought' ejector was a combination ejector, with both large and small ejectors within the same body.[5] The vacuum produced depended on the total number of vehicles in the train and the sum of their various minor leaks. A train of stock due for maintenance could make it difficult to maintain a vacuum, even requiring intermittent use of the large ejector when running. The widely used Super-Dreadnought ejector combined a large ejector with two small ejectors in one.[6] If needed, two of the smaller nozzles could produce more vacuum, yet were more efficient in their use of steam then a single larger nozzle.[3]
The Great Western Railway was noted for its idiosyncrasies, including the use of a higher brake vacuum than other lines. To maintain this without excessive steam consumption in an ejector, they also favoured the use of a crosshead-driven mechanical pump.[6]
Being lazy so took this text from Wikipedia
Ejectors[edit]
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Driver's brake control on a combined control and ejector. The ejector steam nozzles, large and small, are beneath the hexagonal brass plugs on the left.
Vacuum brakes were initially favoured over air brakes because of the ease of producing the vacuum. A vacuum ejector was a simpler and reliable device, compared to the reciprocating pump.[3]
Typically two ejectors are fitted, large and small. The large ejector is used to 'blow off' the brakes, by producing the vacuum, and is then shut off. The small ejector is left running continuously in order to maintain it.[4] The Gresham & Craven 'Dreadnought' ejector was a combination ejector, with both large and small ejectors within the same body.[5] The vacuum produced depended on the total number of vehicles in the train and the sum of their various minor leaks. A train of stock due for maintenance could make it difficult to maintain a vacuum, even requiring intermittent use of the large ejector when running. The widely used Super-Dreadnought ejector combined a large ejector with two small ejectors in one.[6] If needed, two of the smaller nozzles could produce more vacuum, yet were more efficient in their use of steam then a single larger nozzle.[3]
The Great Western Railway was noted for its idiosyncrasies, including the use of a higher brake vacuum than other lines. To maintain this without excessive steam consumption in an ejector, they also favoured the use of a crosshead-driven mechanical pump.[6]
As above but in summary!
Vacuum, free from a steam engines ejector with no moving parts. Limited to pressure differential of 1 bar - i.e. atmospheric pressure down to nothing.
Air, requires a compressor with moving parts, but can be far more effective with a working pressure of up to 10 bar.
An air leak is also far easier to find than a vacuum leak!
Sorry though, I don't understand the pneuvac part!
Vacuum, free from a steam engines ejector with no moving parts. Limited to pressure differential of 1 bar - i.e. atmospheric pressure down to nothing.
Air, requires a compressor with moving parts, but can be far more effective with a working pressure of up to 10 bar.
An air leak is also far easier to find than a vacuum leak!
Sorry though, I don't understand the pneuvac part!
appart from the brilliant 2 desciptons by random grinch and bernard green
general comments
brakes on passenger trains must be continuous from end to end and there must be a way for passengers to give alarm warning on old trains pulling the alarm cord causes the brakes to go on by making a big hole in the brake pipe or a speaker connection to the driver allowing controlled action dependent on actual emergency
general comments
brakes on passenger trains must be continuous from end to end and there must be a way for passengers to give alarm warning on old trains pulling the alarm cord causes the brakes to go on by making a big hole in the brake pipe or a speaker connection to the driver allowing controlled action dependent on actual emergency
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Pneuvac is the name given to the ejector in industry, where instead of steam it used compressed air, all the passenger carriages use a brake using a partial vacuum well OK no such thing really vacuum means no air, so bad English to refer to partial vacuum, but this is because we normally use steam, so if we use diesel like this
some method is required to produce the vacuum, however it seems the ejector is not permitted, they have to have a vacuum pump fitted, the exhauster the same things were used to suck up milk and empty grids on the road side, so I have seen these many times, a more sophisticated type was used with blowers where the paddles did not rub on the outer shell but were held off.
With the Milk Tanker the pump was electrically driven as did not want a diesel engine running in farm yards, and the vehicle had Nickel Iron batteries to run the pump.
So as an ex-motor vehicle fitter producing a vacuum seems easy, with either an air powered or electric powered vac pump, but it seems not allowed to use these with trains, and I can't understand why. OK these
are only like an alternator to fit, so sure the engine can be modified, but why are electric and air powered units not permitted.
some method is required to produce the vacuum, however it seems the ejector is not permitted, they have to have a vacuum pump fitted, the exhauster the same things were used to suck up milk and empty grids on the road side, so I have seen these many times, a more sophisticated type was used with blowers where the paddles did not rub on the outer shell but were held off.With the Milk Tanker the pump was electrically driven as did not want a diesel engine running in farm yards, and the vehicle had Nickel Iron batteries to run the pump.
So as an ex-motor vehicle fitter producing a vacuum seems easy, with either an air powered or electric powered vac pump, but it seems not allowed to use these with trains, and I can't understand why. OK these
Thanks,
I hadn't heard of the pneuvac.
It looks as though the exhauster uses the same principal as a laboratory rotary vane vacuum pump; and as such relies on a film of oil to maintain a seal between the vanes and the casing.
Oil contamination of the milk would not be desirable!
They also consume a quantity of oil in use that is smoked out of the exhaust.
Or could it be that a safety critical system would be relying on other systems, with multiple points of failure?
Sorry, don't know!
I hadn't heard of the pneuvac.
I suspect there may have been a slight difference for the milk pumps.
It looks as though the exhauster uses the same principal as a laboratory rotary vane vacuum pump; and as such relies on a film of oil to maintain a seal between the vanes and the casing.
Oil contamination of the milk would not be desirable!
They also consume a quantity of oil in use that is smoked out of the exhaust.
I can only guess that there could be so little demand for such units, that to get them certified for rail use would be untenable?
Or could it be that a safety critical system would be relying on other systems, with multiple points of failure?
Sorry, don't know!
completely random comments
you could drive a southern region 1963 stock with only air brakes have a class 73 edl loco or a class 419 mlv in the middle and vacuum mail vans at the back all under full control off the driver at the front as mlvs and edls have a proportional valve that only works one way as in converts air brake pressure to vacuum as they have a vacuum exhauster so air must be leading
you could drive a southern region 1963 stock with only air brakes have a class 73 edl loco or a class 419 mlv in the middle and vacuum mail vans at the back all under full control off the driver at the front as mlvs and edls have a proportional valve that only works one way as in converts air brake pressure to vacuum as they have a vacuum exhauster so air must be leading
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What versatile little locos the 73's are!
I've seen 73118 out many times near me, making some very unusual stock moves
I've seen 73118 out many times near me, making some very unusual stock moves
lovely locos but on diesel because off the way the field diverts kick in on any heavy gradient your stuck at around 28mph max as it kicks in and out dropping back to around 23mph before regrouping back to series very frustrating as if you could "hold " series you may get perhaps constant 35 mph indeed thumpers with the same engine would be perhaps 45mph at welcome bridge at the top off dorking bank [1 in 96]What versatile little locos the 73's are!
I've seen 73118 out many times near me, making some very unusual stock moves
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But local line has a 16 MPH speed limit, so not really a problem with 2'6" gauge.lovely locos but on diesel because off the way the field diverts kick in on any heavy gradient your stuck at around 28mph max as it kicks in and out dropping back to around 23mph before regrouping back to series very frustrating as if you could "hold " series you may get perhaps constant 35 mph indeed thumpers with the same engine would be perhaps 45mph at welcome bridge at the top off dorking bank [1 in 96]
ahh ok i dont know if the light railway act applies equally to narrow gauge as 4ft 8 i assume it does but i dont know
i would assume continual braking and communication in emergency still applies from end to end ??
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Not seen an emergency cord, guess the guard can apply brakes, but not general public, unlike main line there is also a veranda, 
at 16 MPH OK, would not want to go outside at 30 MPH.
at 16 MPH OK, would not want to go outside at 30 MPH.
Lol. I see what you did there. Spelling and grammar. Is that the same as not making head nor tail? Comma's in the wrong place too. Just sayin'.
LOL, I see what you did there. Apostrophe not needed lol.