Class 158 Step One

[TheEdge]

This query is based solely on my experience of driving 158s belonging to EMT, so I don't know if this is true across the entire fleet

When braking we are advised to start braking in step 2 the move it back to step 1 to get a full step 1 application. If we just go to step 1 all you get is a very gentle braking action rather than a proper application. This isn't unique to one unit, it seems true for all 158s.

Does anyone know why? Is it an intentional feature to help with maintaining high speed on falling gradients perhaps? Or is it just a quirk of the braking system?

TIA

 

[Wst71Pa2]

I was thinking the same the other day whilst cursing the effectiveness of Step 1 for a Morpeth board.

ScotRail policy is that first application is step 2

 

[Eccles1983]

I think all disc brakes units are step 2 for the initial brake.

 

[CC 72100]

Interesting discussion here.

Whilst I can't offer an answer to the question, on 165/166 if you go from step 2 to step 1 then you get about 0.5 bar extra than when you just go to step 1 only.

Indeed we too are first application in step 2. For those that use a lot of step 1, this often means a 5 mile an hour reduction in step 2 and then back to step 1 for the remainder of the braking.

In some places I'll use step 1 only - for example a gentle 60 to 50 where I'm coasting already having done 70 to 60 as it is sufficient enough to gradually bring the speed down and there is no great rush or high initial speed to kill.

 

[Fincra5]

Interesting discussion here.

Whilst I can't offer an answer to the question, on 165/166 if you go from step 2 to step 1 then you get about 0.5 bar extra than when you just go to step 1 only.

Indeed we too are first application in step 2. For those that use a lot of step 1, this often means a 5 mile an hour reduction in step 2 and then back to step 1 for the remainder of the braking.

In some places I'll use step 1 only - for example a gentle 60 to 50 where I'm coasting already having done 70 to 60 as it is sufficient enough to gradually bring the speed down and there is no great rush or high initial speed to kill.

Thats noticeable on 313s too. We're told to use Step 2 Initial. Of course for low speed decrease it isn't necessary. 377s with Regen aren't required to have Step 2 initial (unless its leaf-fall season).

 

[sw1ller]

Same for the TfW 158’s too. Like has been said, I’ll use step one only if I need to reduce the speed by 5-10 mph, mainly for comfort but I wouldn’t use it for anything greater (usually). I’ve been in a vehicle that suffered from brake fade once and it was like flicking a switch, so I’m quite weary of it now and don’t like over using them.

 

[TheEdge]

I think all disc brakes units are step 2 for the initial brake.

The only other disc braked stock I drive is 170s and they don't seem afflicted by it, into step 1 to start with will happily give you a full step 1 that is often plenty to bring it to a stop.

Nothing like the land anchors fitted to the 156s though!

 

[bengley]

A BR training video somewhere on youtube (I think for 321s) states a step 3 initial brake application is ideal, then reducing to 2 or 1 as necessary (apt considering the class of unit!)

 

[hexagon789]

A BR training video somewhere on youtube (I think for 321s) states a step 3 initial brake application is ideal, then reducing to 2 or 1 as necessary (apt considering the class of unit!)

I think that technique was ammended soon after, certainly it's not common practice now. BR switched from Step 3 initial with disc-braked units for several reasons:

Such liberal use of Full Service was costing a fortune in disc pads.

If a driver misjudged the braking point, he couldn't brake any harder (most units at the time didn't have enhanced emergency braking, emergency simply gave a fail-safe full brake application but no greater brakeforce).

It was leading to station overruns in poor rail conditions.

Certainly since the early 1990s, Step 2 intially has been common and I believe Step 1 or 2 initial is the policy of all TOCs, I don't think any have Step 3 initial policies anymore.

Nevertheless, use Step 3 is of course allowed in normal service, primarily for 'correcting' retardation as necessary but over-reliance on it is generally frowned upon.

 

[bengley]

I think that technique was ammended soon after, certainly it's not common practice now. BR switched from Step 3 initial with disc-braked units for several reasons:

Such liberal use of Full Service was costing a fortune in disc pads.

If a driver misjudged the braking point, he couldn't brake any harder (most units at the time didn't have enhanced emergency braking, emergency simply gave a fail-safe full brake application but no greater brakeforce).

It was leading to station overruns in poor rail conditions.

Certainly since the early 1990s, Step 2 intially has been common and I believe Step 1 or 2 initial is the policy of all TOCs, I don't think any have Step 3 initial policies anymore.

Nevertheless, use Step 3 is of course allowed in normal service, primarily for 'correcting' retardation as necessary but over-reliance on it is generally frowned upon.

Indeed. The policy at TL with 319s was a step 3 running brake test at 80-90mph, with a 10mph reduction in speed in order to condition the brake pads and allow the slack adjusters to do their thing. You really could feel the difference even in step 1 and 2 after doing such a brake test.

 

[hexagon789]

Indeed. The policy at TL with 319s was a step 3 running brake test at 80-90mph, with a 10mph reduction in speed in order to condition the brake pads and allow the slack adjusters to do their thing. You really could feel the difference even in step 1 and 2 after doing such a brake test.

I imagine giving it a strong application like that heats the pads up and gives better brake performance and more bite, rather as with a car.

On my local line, all 156s, drivers nearly always make a running brake test application at the same point, unless having to slow previously for signals. When they perform this however, it seems to vary driver-to-driver - some brake quite lightly (presumably Step 1), others harder (presumably Step 2) and often hold the application for different amounts of time (as though some shave of say 5mph and others 10-15).

 

[londonmidland]

Certainly no expert in this field of topic though I find the 156's have pretty solid brakes. You can certainly hear and feel a (I think) step 2 brake application. Same goes for the 150's, too.

 

[Llama]

Step 1 brake on a Westcode EPB1 brake is/was only intended as a 'holding' brake, not for actual retardation. Some companies have a policy which includes the permitted use of step 1 brake to maintain speed (eg on steep falling gradients) or to slow the train gently at low speeds or in low adhesion conditions. However a 'normal' brake application should be initially step 2.
Step 1 on a Westcode brake in a tread braked unit (eg 156) equates to approx 0.3m/s^2 (3%g) deceleration, on a Westcode unit with disc brakes the rate of deceleration would be less than that.

 

[JonathanP]

Nevertheless, use Step 3 is of course allowed in normal service, primarily for 'correcting' retardation as necessary but over-reliance on it is generally frowned upon.

Step 1 brake on a Westcode EPB1 brake is/was only intended as a 'holding' brake, not for actual retardation. However a 'normal' brake application should be initially step 2.

So discounting the 'retardation' notch and the 'reserve' notch, you actually only have one choice, Brake(Step 2), or don't brake(Release), right? I am both baffled and impressed that British drivers can drive efficently under these conditions.

I have always found the seemingly purposeful simplicity of UK cab controls a little strange. In Germany the standard setup has 9 brake notches. In the computer-controlled traction era there is to need to have power notches on units at all, yet British cabs seem to stick stubbornly with providing a fixed set of noteches instead of having a inifintely variable controller.

 

[hexagon789]

So discounting the 'retardation' notch and the 'reserve' notch, you actually only have one choice, Brake(Step 2), or don't brake(Release), right? I am both baffled and impressed that British drivers can drive efficently under these conditions.

I have always found the seemingly purposeful simplicity of UK cab controls a little strange. In Germany the standard setup has 9 brake notches. In the computer-controlled traction era there is to need to have power notches on units at all, yet British cabs seem to stick stubbornly with providing a fixed set of noteches instead of having a inifintely variable controller.

Not all British trains have a 3-step brake mind you. A lot of more modern stuff has a fully variable brake such as the various Desiro units (185, 380, 444, 450), fairly certain 334s, 175s and 180s are also fully variable. High-speed stuff such as InterCity 125s and 225s have six service brake steps.

I think that if a driver knows their route well, having only 3 brake levels isn't all that inflexible, I believe that on units/trains with fully variable braking, drivers are often taught to treat certain levels of braking as akin to 'steps' and brake based on that rather than making use of small, incremental adjustments.

 

[Bigfoot]

On the majority of 3 step brake units making a step 2 or above application means if youve left the power handle open then it cuts the power aswell as applying the brakes.

 

[anamyd]

Not all British trains have a 3-step brake mind you. A lot of more modern stuff has a fully variable brake such as the various Desiro units (185, 380, 444, 450), fairly certain 334s, 175s and 180s are also fully variable. High-speed stuff such as InterCity 125s and 225s have six service brake steps.

I think that if a driver knows their route well, having only 3 brake levels isn't all that inflexible, I believe that on units/trains with fully variable braking, drivers are often taught to treat certain levels of braking as akin to 'steps' and brake based on that rather than making use of small, incremental adjustments.

Desiros are German and Coradias/Junipers are French

 

[Llama]

On the majority of 3 step brake units making a step 2 or above application means if youve left the power handle open then it cuts the power aswell as applying the brakes.

That's true, but the main intent of the design was to allow a driver to hold the train using step 1 brake when taking traction power when starting away (especially on rising gradients).

 

[hexagon789]

Desiros are German and Coradias/Junipers are French

And fully variable braking seems pretty common on Continental multiple units.

Though I get the impression that many German and Dutch units seem to have stepped braking though with far more notches than we have here (7 or 9 seems common).

 

[43096]

I have always found the seemingly purposeful simplicity of UK cab controls a little strange. In Germany the standard setup has 9 brake notches. In the computer-controlled traction era there is to need to have power notches on units at all, yet British cabs seem to stick stubbornly with providing a fixed set of noteches instead of having a inifintely variable controller.

Having power notches and brake steps does have an advantage in that it is inherently suitable for digital control, as train wires can be energised (or not) to transmit the relevant notch/step to other units. The HST multi-working system is a good example and is failsafe - and no control air pipes to faff around with either.

 

[Railengineer]

Having power notches and brake steps does have an advantage in that it is inherently suitable for digital control, as train wires can be energised (or not) to transmit the relevant notch/step to other units. The HST multi-working system is a good example and is failsafe - and no control air pipes to faff around with either.

Just for the record HST's have a digitally-controlled two-pipe brake control system, so there are plenty of '....air pipes to faff around with' !

 

[Railengineer]

This query is based solely on my experience of driving 158s belonging to EMT, so I don't know if this is true across the entire fleet
When braking we are advised to start braking in step 2 the move it back to step 1 to get a full step 1 application. If we just go to step 1 all you get is a very gentle braking action rather than a proper application. This isn't unique to one unit, it seems true for all 158s.

Does anyone know why? Is it an intentional feature to help with maintaining high speed on falling gradients perhaps? Or is it just a quirk of the braking system?

TIA

Interesting question;
The three-step braking system is designed for simplicity and reliability. The braking on each vehicle is applied consistently throughout the train and the brake pad friction is almost even at all speeds. The three steps provide a low-medium-high selection of brake force which should be managed according to the driving conditions. In most cases under tare (no load) conditions STEP 1 brake equates approximately to 1 bar brake cylinder pressure, STEP 2 equates to approximately 2 bar pressure and STEP 3 equates to approximately 3 bar pressure. Load weighing proportionately increases the brake cylinder pressure by up to 50 % as the passenger load increases. Whilst there are slight pressure variations across all types of rolling stock, the principles are the same for all. The reasoning behind what step is selected first really comes from the train operators driving policy. There is no technical advantage in selecting step 2 then step 1 if you really only want step 1, any suggestion to the contrary is just driver perception. You are not decelerating when you go straight to step 1 so you have nothing to compare the lighter application with, whereas when going step 2 to step 1 it is easy to perceive the difference and you think it is greater.
Some of the posts here suggest that step 1 is not effective? If you apply step 1 at speed and leave it there the train will stop, albeit in 2/3 greater distance (approx) than a step 3 application. Try it sometime.

 

[Llama]

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.

 

[43096]

Just for the record HST's have a digitally-controlled two-pipe brake control system, so there are plenty of '....air pipes to faff around with' !

I’m well aware of how the HST brake control system works, thanks. You are somewhat subjectively quoting about air pipes when I made a specific reference to CONTROL air pipes in reference to (in particular) the blue star system - nothing to do with brake pipes.

 

[CC 72100]

Interesting question;

There is no technical advantage in selecting step 2 then step 1 if you really only want step 1, any suggestion to the contrary is just driver perception. You are not decelerating when you go straight to step 1 so you have nothing to compare the lighter application with, whereas when going step 2 to step 1 it is easy to perceive the difference and you think it is greater.
Some of the posts here suggest that step 1 is not effective? If you apply step 1 at speed and leave it there the train will stop, albeit in 2/3 greater distance (approx) than a step 3 application. Try it sometime.

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?

 

[37057]

Not all British trains have a 3-step brake mind you. A lot of more modern stuff has a fully variable brake such as the various Desiro units (185, 380, 444, 450)

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.

 

[Wst71Pa2]

Interesting question;
The three-step braking system is designed for simplicity and reliability. The braking on each vehicle is applied consistently throughout the train and the brake pad friction is almost even at all speeds. The three steps provide a low-medium-high selection of brake force which should be managed according to the driving conditions. In most cases under tare (no load) conditions STEP 1 brake equates approximately to 1 bar brake cylinder pressure, STEP 2 equates to approximately 2 bar pressure and STEP 3 equates to approximately 3 bar pressure. Load weighing proportionately increases the brake cylinder pressure by up to 50 % as the passenger load increases. Whilst there are slight pressure variations across all types of rolling stock, the principles are the same for all. The reasoning behind what step is selected first really comes from the train operators driving policy. There is no technical advantage in selecting step 2 then step 1 if you really only want step 1, any suggestion to the contrary is just driver perception. You are not decelerating when you go straight to step 1 so you have nothing to compare the lighter application with, whereas when going step 2 to step 1 it is easy to perceive the difference and you think it is greater.
Some of the posts here suggest that step 1 is not effective? If you apply step 1 at speed and leave it there the train will stop, albeit in 2/3 greater distance (approx) than a step 3 application. Try it sometime.

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.

 

[sw1ller]

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.

Now that’s interesting. Personally, I prefer a weak step 1 and then a strong step 2, but this sounds like an actual maintenance issue and it’s quite scary.

 

[superkev]

Wasn't defensive driving highlighted as one of the reasons for delays round Waterloo.
Fans of Japanise railways may want to look at 1 min 25 of youtube video

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

 

[Railengineer]

I’m well aware of how the HST brake control system works, thanks. You are somewhat subjectively quoting about air pipes when I made a specific reference to CONTROL air pipes in reference to (in particular) the blue star system - nothing to do with brake pipes.

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?