On the London Underground trains there was a "rate switch", that could be switched to give a lower than normal rate of acceleration in conditions of low adhesion. Was there something similar on BR electric multiple units?
Coasting Control on D78s is nothing to do with the rate of notching of the equipment.
That was (and still is) selected by selecting FOR1 or FOR2 on the Reverser Switch, the Coasting Control Cut Out Switch cuts out the coasting control relays, which cut traction power at a speed determined by the speed sensing equipment.
Weak field simply allows the weak field contractors to come in by enabling the weak field wires when the Combined Traction Brake Controller is in Parallel.
The "Rate Switch" on D78 was formed up as part of the Reverser Switch and coded up into the Traction Control Coding wires 1-3 on circuits A and D.
The first mass produced LUL stock not to have a rate switch or rate selection of some kind was 1992TS.
Some SR Stock as a similar selection, with "Emergency Rate" being available on the DC Powered Class 442s for example, this has also been carried forwards into other fleets and retractions to include "Power Reduction" modes.
As a more general note, although using the rate switch did make you accelerate slower, it did nothing to help wheel slip in the 1st series notch and very little in the 1st parallel notch, hence why wheel slip relays were introduced on LUL stock for the last two or three interactions of camshaft controlled equipment.
All you have to do on an EPB is rather than leave it in series, for example to run up to full series, is to go to series and swiftly back to shunt to hold a lower level of amps then repeating when required rather than the current limit relay dictating a much higher level.
It is correct, 72ts on the Bakerloo have rate switches. Normal service is using Rate 2 but if adhesion problems then we can switch it to Rate 1.I'm just repeating the information I got off District Dave's website. As a driver I assumed his information would be accurate.
It is correct, 72ts on the Bakerloo have rate switches. Normal service is using Rate 2 but if adhesion problems then we can switch it to Rate 1.
But we can also hand notch it which gives us a bit more control, we can also hand notch in Rate 1 too but it's verrry slow only useful for fully iced rails. Most of us just keep it in Rate 2 and hand notch it if needed.
To hand notch, you hold the TBC (traction brake controller) in shunt, slip it in to series, let the cams take away one bit of resistance (one click) and back into shunt. You can repeat in twice more until you reach full series. You can't however do it between series and parallel but by that point you should be doing a good enough speed to have enough grip.
The closest thing would be the 'Series only' switch on 400 stock. However this was normally used where the power supply to the third rail couldn't handle the power taken if a train went into parallel or weak field. The only place I can recall the use of this being mandated was between Seaford and Newhaven Harbour if formed of more than 4 coaches. It wasn't used for low adhesion purposes, as stated above the use of the hand notching technique was used at those times.
Paul
The series only switch was also used on 4CEP units between Folkestone Harbour and Folkestone Junction.The closest thing would be the 'Series only' switch on 400 stock. However this was normally used where the power supply to the third rail couldn't handle the power taken if a train went into parallel or weak field. The only place I can recall the use of this being mandated was between Seaford and Newhaven Harbour if formed of more than 4 coaches. It wasn't used for low adhesion purposes, as stated above the use of the hand notching technique was used at those times.
Paul
Not strictly true as I believe the Mk1s have it on the reverser rather than the No.4 switch panel.It is correct, 72ts on the Bakerloo have rate switches. Normal service is using Rate 2 but if adhesion problems then we can switch it to Rate 1.
But we can also hand notch it which gives us a bit more control, we can also hand notch in Rate 1 too but it's verrry slow only useful for fully iced rails. Most of us just keep it in Rate 2 and hand notch it if needed.
To hand notch, you hold the TBC (traction brake controller) in shunt, slip it in to series, let the cams take away one bit of resistance (one click) and back into shunt. You can repeat in twice more until you reach full series. You can't however do it between series and parallel but by that point you should be doing a good enough speed to have enough grip.
Brake rates depend heavily on the generation of stockThanks, not being au fait with LUL stock you have to take what little information there is at face value. With the braking rates, how much of a difference is it? Is it 50% vs 100% or less of a difference 75% against 100%?
They do indeed but we're still able to change the rate of acceleration, you could call it a "rate switch".Not strictly true as I believe the Mk1s have it on the reverser rather than the No.4 switch panel.
Brake rates depend heavily on the generation of stock
EP brakes do a set retardation rate set by the retarders for example. (Only on 72TS now)
Westcode braked does technically have loadweigh to balance the rates, but it rarely works.
Smart valve units are much l, well, smarter.
The series only switch was also used on 4CEP units between Folkestone Harbour and Folkestone Junction.
Indeed, it was to allow drivers to take weak field power in series to make the best use off power available for the steep grade.The series only switch was also used on 4CEP units between Folkestone Harbour and Folkestone Junction.
The only one that truly matters is the EB Rate, and that should be the same on all stocks as part of S1180, 1-180 or however far back in the standards you want to go.I was meaning more what the difference between the rates on one stock type is rather than of different stocks
The only one that truly matters is the EB Rate, and that should be the same on all stocks as part of S1180, 1-180 or however far back in the standards you want to go.
Nothing, it's acceleration only. You still get a full rheostatic brake.But what does the rate switch do to the braking rate? That's what I was asking, sorry.
Nothing in pneumatic. I'd need to check the schemes for rheo braking, but on D78 it's nothing whatsoever, the rate coil isn't brought in as part of the braking curve, that's just brought in by 0 and 29 wire and takes its ques from Westcode. The "rate" coding isn't sent.But what does the rate switch do to the braking rate? That's what I was asking, sorry.
Is a discussion I've had many times that Reho braking should be allowed to be cut out, but it should be operationally nessesary and monitored.Nothing, it's acceleration only. You still get a full rheostatic brake.
We have ways of avoiding using the rheo brake but there's no way to cut it out.
First way is to use the Westinghouse brake, this is purely mechanical and if used properly can give a nice smooth stop.
Another way is to "fan the handle" where you go from "off and release" round to "Max EP" and back again quickly, this doesn't give enough time for the rheo brake to kick in but you still get some brake applying, you have to do this multiple times over a long stretch.
When the train gets below 19mph and you start braking then the rheo won't come on and you just get normal EP. There's 3 steps of EP (technically 4 if you include the holding brake), minimum, normal and max which give enough control to avoid a slide.
There's other braking methods that some drivers use but I won't go in to details on those!
Nothing, it's acceleration only. You still get a full rheostatic brake.
We have ways of avoiding using the rheo brake but there's no way to cut it out.
First way is to use the Westinghouse brake, this is purely mechanical and if used properly can give a nice smooth stop.
Another way is to "fan the handle" where you go from "off and release" round to "Max EP" and back again quickly, this doesn't give enough time for the rheo brake to kick in but you still get some brake applying, you have to do this multiple times over a long stretch.
When the train gets below 19mph and you start braking then the rheo won't come on and you just get normal EP. There's 3 steps of EP (technically 4 if you include the holding brake), minimum, normal and max which give enough control to avoid a slide.
There's other braking methods that some drivers use but I won't go in to details on those!
Nothing in pneumatic. I'd need to check the schemes for rheo braking, but on D78 it's nothing whatsoever, the rate coil isn't brought in as part of the braking curve, that's just brought in by 0 and 29 wire and takes its ques from Westcode. The "rate" coding isn't sent.
On Westcode stock it's one or the other.Thank you, I've obviously misunderstood a previous post. So braking is a sort of 4-step Westcode with rheo overlaid?
I've heard that the emergency setting was for use in the tunnels on the Watford DC route out of Euston if one of the powered bogies failed in use.I have an old book that says the North London (Broad Street) units, (later class 501 ?) had a special setting for emergency towing of another unit
Will try and find it
On Westcode stock it's one or the other.
The Westcode braking is inhibited when Reho braking is proven on a car by car basis (essentially).
EDIT: provided you're over the Reho enabled speed.
Bakerloo Line 1972TS is done differently.
Only Westcode stock on LUL left with Reho now is 1973TS.
I've heard that the emergency setting was for use in the tunnels on the Watford DC route out of Euston if one of the powered bogies failed in use.