Class 158 Step One

[Railengineer]

Unless it's a ScotRail 158, regularly less than 1 bar in 1 and a marked deterioration over the last month or so. 1 was usually enough for a PSR/TSR, not recently.

Ah good old Scotrail....did they fit all the brake pads?

 

[Railengineer]

The difference when driving a mixed formation of tread and disc braked vehicles is quite marked from that of just one type. There is no way that applying step 1 brake in the same general location at the same speed with a mixed tread/disc formation (say 150+158) can be relied on at all to brake the train in the same distance.

Tread brakes seem to adhere more linearly to the 1/3 - 2/3 - 3/3 principle in brake step 1/2/3 respectively, disc brakes throw that linearity out. A tread brake in say a 150 is more 'progressive' than the disc brakes on 158s - eg the slower your speed, the more effective the brake is but this effect seems much less pronounced in 158s which brake from higher speeds much better.

Indeed, tread brakes are a whole different story due to the variable friction at different speeds

 

[Railengineer]

Unless you have a train, such as the 165/166 whereby a step 2 then to step 1 within a few seconds results in about 0.4/0.5 higher bar in step 1 than the equivalent pressure if you go into step 1 directly.

I don't know if there are any other trains like that?

I used to work on these and don't think recall them doing it to that extent. There can be a slight difference due to the system hysteresis sometimes caused by the relay valve balance, but this should not be relied upon to provide an increased brake force

 

[Wst71Pa2]

Ah good old Scotrail....did they fit all the brake pads?

You know you're in for fun when the last entry in the fault book is a brake pad change

 

[Llama]

With the Westcode three step brakes I have driven there is sometimes (but not always) a slight increase in step 1 pressure if reducing from step 2 to step 1, but only maybe 0.1 bar. I have never noticed one give more than this amount though. Recently I was trying to demonstrate to a trainee driver this 'characteristic' and the pressures on the unit in question were exactly the same regardless of step 1 being selected from release or from step 2, which served as a good demonstration that this doesn't always happen and obviously shouldn't be relied upon.

 

[CC 72100]

I used to work on these and don't think recall them doing it to that extent. There can be a slight difference due to the system hysteresis sometimes caused by the relay valve balance, but this should not be relied upon to provide an increased brake force

Interesting - I'll do some investigations.

Agreed, never rely on the increased force that way, and indeed it isn't always helpful nor desired!

 

[37057]

Ops sorry, I only quoted your exact words...I thought the train pipe provided brake control pressure but will bow to your superior knowledge. Perhaps you can enlighten me as to the 'blue star' braking system you are referring to please?

Blue star isn't a braking system, it's a multiple working system used on old locos. 'Control air pipes' are used to control the speed of the trailing locos engine while electric train wires control the switchgear etc.

Not sure what relevance it is to this thread though.

 

[43096]

Ops sorry, I only quoted your exact words...I thought the train pipe provided brake control pressure but will bow to your superior knowledge. Perhaps you can enlighten me as to the 'blue star' braking system you are referring to please?

It’s the blue star multiple working system that I’m referring to in my original post, nothing to do with brakes. It is an electro-pneumatic system.
https://en.m.wikipedia.org/wiki/Multiple_working

 

[Bigfoot]

Straight to full power. Non of our pussy cat driving there.

Which is exactly what I do. Unless it's slippy...

 

[EvoIV]

Vaguely related, if you're driving a train with a class 70 loco on the front you have to make your initial application at more than initial (you can then come back to initial if you want) to gain the dynamic brake, which is like a rheostatic brake. If you linger in initial too long you lose the dynamic brake again, so you have to release the brake, pause, then reapply to regain the dynamic brake. Makes hitting a stopping point a bit more interesting, not that it is often that critical on freight.

 

[Railengineer]

It’s the blue star multiple working system that I’m referring to in my original post, nothing to do with brakes. It is an electro-pneumatic system.
https://en.m.wikipedia.org/wiki/Multiple_working

Bit off topic then really...

 

[hexagon789]

Those units still have three-step braking. Electrical contacts closed (and opened) by the position of the power/brake controller. In addition the same camshaft drives an encoder for variable brake.

I know it's a form of EP braking control but I'm sure it's fully variable rather than 3 fixed steps plus emergency.

 

[Railengineer]

I know it's a form of EP braking control but I'm sure it's fully variable rather than 3 fixed steps plus emergency.

If referring to Desiro's then you are correct.

 

[hexagon789]

If referring to Desiro's then you are correct.

I'm referring to all of:

444, 450 and 185s

 

[HLE]

Desiro's are variable. Good brake too.

 

[37057]

I know it's a form of EP braking control but I'm sure it's fully variable rather than 3 fixed steps plus emergency.

Three step is there though. The PBC isn't notched for the three step but the microswitches, relays and train wires are there should the variable feature fault.

I've driven enough of them (in redundancy mode too), changed enough PBCs, relay cards and dealt with the schematics often enough to know that much!

The power settings are almost opposite though, they are clearly notched but the variable feature work too (in between each notch).

 

[hexagon789]

Three step is there though. The PBC isn't notched for the three step but the microswitches, relays and train wires are there should the variable feature fault.

I've driven enough of them (in redundancy mode too), changed enough PBCs, relay cards and dealt with the schematics often enough to know that much!

The power settings are almost opposite though, they are clearly notched but the variable feature work too (in between each notch).

I'm sure the base system is there, but it isn't "pure" 3-step as ordinarily it's full variable.

That's what I'm driving at.

Interesting, I hadn't realised one could 'bypass' the five power notches, must be useful for when you want to hold a speed for a bit.

 

[37057]

You're right that ordinary it's variable but also ordinarily, is that both systems are used together. It's just that the three step aspect is descrete. If you drive them, feel for the microswitches, you'll hear the relays working in the cupboard behind you. They're more noticeable on an EMU as they use a pair of bulky relays as apposed to a compact relay card in the DMU's. The BCU will take whatever signal is higher whether it be the MVB signal (originally produced by the encoder) or mode wires. OTMR traces the PBC position by the mode wires.

I would have thought drivers are made aware of this as if there was ever a situation where the variable brake ceased to function, they'd know where they need to put the PBC, brake control is a lot more coarse!

Only four power notches though, that extra one doesn't provide any more power but acts as a speed set position.

 

[hexagon789]

You're right that ordinary it's variable but also ordinarily, is that both systems are used together. It's just that the three step aspect is descrete. If you drive them, feel for the microswitches, you'll hear the relays working in the cupboard behind you. They're more noticeable on an EMU as they use a pair of bulky relays as apposed to a compact relay card in the DMU's. The BCU will take whatever signal is higher whether it be the MVB signal (originally produced by the encoder) or mode wires. OTMR traces the PBC position by the mode wires.

I would have thought drivers are made aware of this as if there was ever a situation where the variable brake ceased to function, they'd know where they need to put the PBC, brake control is a lot more coarse!

Only four power notches though, that extra one doesn't provide any more power but acts as a speed set position.

No, I don't drive Desiros, nor any train for that matter - I just have an interest in the nore technical side of things.

As a non-driver I don't feel I can say whether fixed or variable braking is truly better from a handling point of view, but it seems to me that being able to make more incremental adjustments of the brake would be inherently useful.

So if you were to accelerate to say 60mph in Notch 4, if you then go into to Notch 5 it'll hold speed at 60.

 

[37057]

That's not something I'm 100% on, being only a 5mph type driver inbetween fixing them.

I'll start by saying that the extra notch, to make things simple we'll just call it notch 5 (which has the same effect as notch 4).

I think drivers tend to put it in the 5th notch (otherwise you have to concentrate where the 4th is). When you're doing 50 mph and above (I think), they'll put it back a notch (4th) and back into 5th. Whether putting it into 4th at the beginning then 5th to speed set works, I don't know - one for a mainline driver to answer for as I don't have my notes on me. EMUs have a speed set light, DMU's use a shared light with Eco mode / Category A fault, which blinks to say its set. The notch 4 and 5 action is also used to move the units in 'low speed' setting, there's a separate button to press prior to this though. I've only used it for curiosity but it's not very useful, especially on a 185.

 

[hexagon789]

That's not something I'm 100% on, being only a 5mph type driver inbetween fixing them.

I'll start by saying that the extra notch, to make things simple we'll just call it notch 5 (which has the same effect as notch 4).

I think drivers tend to put it in the 5th notch (otherwise you have to concentrate where the 4th is). When you're doing 50 mph and above (I think), they'll put it back a notch (4th) and back into 5th. Whether putting it into 4th at the beginning then 5th to speed set works, I don't know - one for a mainline driver to answer for as I don't have my notes on me. EMUs have a speed set light, DMU's use a shared light with Eco mode / Category A fault, which blinks to say its set. The notch 4 and 5 action is also used to move the units in 'low speed' setting, there's a separate button to press prior to this though. I've only used it for curiosity but it's not very useful, especially on a 185.

Well thanks for the info anyway.