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Post by up1989 on Jan 8, 2018 22:59:36 GMT
Hello all!
Just wondering what the point of the Rate 1/2 switch on the 72 tube stock. I know it slows acceleration but what was the need for it when the stock was produced?
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Post by philthetube on Jan 9, 2018 3:16:29 GMT
I think I initially answered the wrong question but left in the answer as some may find it interesting. Rate 1/2 switch is commonly known by crew as the flag, they exist on many stocks, certainly on S8 stock although not on S7's. They basically are a gearing system which allow Higher top speed or better acceleration. On the Met the flag is down Rate 1 between Finchley Rd and Aldgate and up for the rest of the route. Max speed with flag down is approx 40mph and 60 mph with it up. The operation of the flag is done automatically on S8's. on A stock it was done by the driver. Sorry I dont know more about the Bakerloo but I do know that they were not used on 72 stock on the Northern line. Having re-read your question I realise I may have barked up the wrong tree so here is an alternative answer. From memory I think it was Rake and not rate, but I would not swear to that. If this is the question then you are talking about the option on the control barrel, 1 provides much slower acceleration and is used when tracks are slippery to avoid/reduce wheelspin when moving off. the control key would normally be moved to position to as soon as the train was happily on its way with no wheelspin. Whichever the question I hope this helps.
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Post by Dstock7080 on Jan 9, 2018 7:41:10 GMT
From memory I think it was Rake and not rate, but I would not swear to that. The Rate switch is certainly labelled as such on 1972 Stock, as was on C Stock too. Is located away from the Master Controller and allows different rates of acceleration to be selected by the driver. On other Stock it was in the reverser barrel to be selected by the Reverser (or RKL) Key; 1956/‘59/‘62, 1973, 1983, R, A, D. On A Stock depending on whether the weak-field flag was raised this would lock the acceleration Rate to I. With the flag down Rate II could be used. I’m trying to remember how 1938 Tube Stock were fitted? I seem to recall that on CO/CP Stock there was a separate switch, not unlike a domestic light switch, which altered the Rate. commonly known by crew as the flag, they exist on many stocks, certainly on S8 stock although not on S7's. As an aside, S7 Stock also have an automatic Weak-Field flag, it’s operation only visible to the driver.
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Post by 100andthirty on Jan 9, 2018 8:19:50 GMT
There are two devices here........rate switch and flag switch. They only apply to trains with camshaft.
The rate switch modifies the rate at which the camshaft notches through the resistors, affecting the acceleration rate; rate 2 produces higher acceleration.
The flag switch, which displays a black/yellow tell tale visible from outside, provides field weakening once the train is in full parallel, in practice, it's an extra notch to give extra tractive effort to increase speed.
The rate switch and the flag switch act independently except on A stock where rate 1 is imposed when the flag switch is operated imposing a lower acceleration rate in the higher speed areas for power supply reasons
Of current camshaft trains, as far as I recall, Bakerloo trains don't have a flag switch, and Piccadilly line trains do.
Modern trains with chopper or 3-phase AC control have a variable rate motoring controller instead of rate/series/parallel and the allowable performance is set in software. Uniquely, S stock has a number of pre-set rates to emulate A stock (without the rate 1 restriction, power supply fixed), C/D stock, and the post upgrade setting which will be similar to VLU with a higher top speed. Trains automatically switch between the A and C/D settings using the CSDE system.
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Post by philthetube on Jan 9, 2018 9:29:07 GMT
The reason I said S7's dont have a weak field switch is that they are only capable of 40mph between Finchley Rd. and Harrow so I assumed that was the reason.
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Post by norbitonflyer on Jan 9, 2018 12:05:42 GMT
The reason I said S7's dont have a weak field switch is that they are only capable of 40mph between Finchley Rd. and Harrow so I assumed that was the reason. Capable, or permitted? Presumably the S7+1s can/could do more than 40mph - they would be a bit of a liability for timekeeping otherwise - and it would surely be too much trouble to have had that capability installed, only to be removed when two of them were converted to S7.
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Post by 100andthirty on Jan 9, 2018 12:33:13 GMT
The reason I said S7's dont have a weak field switch is that they are only capable of 40mph between Finchley Rd. and Harrow so I assumed that was the reason. I'm being pedantic, but there is no such thing as "weak field" on three phase ac trains. The required performance is switchable in software via CSDE and it'll be the performance change aspect of that which won't operate if S7s pop up north of Finchley Road. norbitonflyer: S7+1 is, for this purpose, S8 The traction packages and motors are the same on both S8 and S7; both are capable of very considerably more performance than they are currently delivering; wait for the new signalling to be fully commissioned.
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Post by norbitonflyer on Jan 9, 2018 13:01:45 GMT
. The required performance is switchable in software via CSDE and it'll be the performance change aspect of that which won't operate if S7s pop up north of Finchley Road. S7+1 is, for this purpose, S8 The traction packages and motors are the same on both S8 and S7. So the capability can be (realtively) simply switched in or out depending on whether the eight car is present - i.e whether the train is configured as an S7 or an S7+1 ?
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Post by piccboy on Jan 9, 2018 13:45:50 GMT
. The required performance is switchable in software via CSDE and it'll be the performance change aspect of that which won't operate if S7s pop up north of Finchley Road. S7+1 is, for this purpose, S8 The traction packages and motors are the same on both S8 and S7. So the capability can be (realtively) simply switched in or out depending on whether the eight car is present - i.e whether the train is configured as an S7 or an S7+1 ? Configured in software I believe. The weak field flag on S7 is activated east of Bow Road, west of Turnham Green, and memory alludes me on the Wimbledon Branch of the District. In either flag up or down, the S7 are limited to 47mph. And performance wise, instead of seeing 25mph from a standing start at a platform to 7 car passing the headwall barrier flag down, flag up sees about 27/28 mph.
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Post by Dstock7080 on Jan 9, 2018 15:46:34 GMT
In either flag up or down, the S7 are limited to 47mph. In flag-down mode they are limited to 42mph. Putney Bridge is the Wimbledon branch changeover.
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Post by t697 on Jan 10, 2018 6:34:44 GMT
Just curious about the 1973TS Flag switch. Is there any external indicator now? When new there was one built into the original Train Number Indicator just under the offside windscreen. That's gone now.
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Post by 100andthirty on Jan 10, 2018 7:59:41 GMT
I have a vague memory that 73ts was put into permanent flag up performance; I could be wrong
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Post by Dstock7080 on Jan 10, 2018 11:14:12 GMT
Just curious about the 1973TS Flag switch. Is there any external indicator now? When new there was one built into the original Train Number Indicator just under the offside windscreen. That's gone now. I have a vague memory that 73ts was put into permanent flag up performance; I could be wrong Done at refurbishment I believe.
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metman
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Post by metman on Jan 10, 2018 21:05:00 GMT
Was the old flag indicator the Maltese cross icon?
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Post by Deleted on Jan 11, 2018 5:55:47 GMT
I have a vague memory that 73ts was put into permanent flag up performance; I could be wrong Im sure there is a rotary type switch on the offside of the cab by the door which selects weak field could be wrong though been a while since i been in a 73 stock
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towerman
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Post by towerman on Jan 12, 2018 11:19:12 GMT
On the converted 72Mk1s when in rate 2 it often caused loss of pilot light when starting off causing the motors to drop out.On the Mk1s the rate switch selector is on the reverser barrel rather than a separate switch.
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Post by fish7373 on Jan 12, 2018 14:33:22 GMT
Hello all! Just wondering what the point of the Rate 1/2 switch on the 72 tube stock. I know it slows acceleration but what was the need for it when the stock was produced? HI That`s forward 1 and 2 switch selector is on the reverse barrel the 73 tube stock has the same but it is not weak field for wet rails on pull away.
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