Class 86 Brake controls

[leopardml2341]

Hello Folks,

 

Wondering if any Class 86 drivers or ex drivers can tell me a little bit about how the brake controls work?

 

Are the train brakes applied directly from a proportional air control valve on the driver desk or are they applied through an electrical interface controlling solenoid valves?

 

Also were they used with dvt and if so how were the brakes applied from the dvt end, under tdm control or directly acting on the train brake pipe?

 

I’m aware that at higher speeds 110+(?) mph that the brake pipe is vented from both ends e.g. class 91 + dvt.

 

Thanks in anticipation.

 

Andy

[rodent279]

They were used with DVT's. Can't help with any of the rest though.

[DY444]

Hello Folks,

 

Wondering if any Class 86 drivers or ex drivers can tell me a little bit about how the brake controls work?

 

Are the train brakes applied directly from a proportional air control valve on the driver desk or are they applied through an electrical interface controlling solenoid valves?

 

Also were they used with dvt and if so how were the brakes applied from the dvt end, under tdm control or directly acting on the train brake pipe?

 

I’m aware that at higher speeds 110+(?) mph that the brake pipe is vented from both ends e.g. class 91 + dvt.

 

Thanks in anticipation.

 

Andy

 

My understanding is this:

 

86s have an essentially standard air controlled system however the drivers brake valve has micro switches incorporated and when the valve is moved towards the First Application position those micro switches trigger the initialisation of the rheo brake.  Once initialised a system of relays and valves regulate the degree of rheo braking according to the brake pipe pressure set by the position of the drivers brake valve.  When the rheo fades at low speed or fails the air brake on the locomotive is automatically ramped up to compensate. 

 

86s did work with DVTs but the brakes could only be applied from the leading end via the brake pipe in the normal way.  This was also the case for 87s. 

Edited May 9, 2018 by DY444

[seraphim]

I think that description is pretty good. I cannot remember if anything happened as a consequence of the brief loss of rheo when the loco passed through a neutral section. One clever feature of Class 90 was the ability to continue Rheo braking even through a neutral.

 

DVT plus Class 90 could have brake operation at both ends, similar to HST; the DW3 unit on the loco (or DVT, if loco leading) could be controlled via the TDM system. However, I recall that in practice, this wasn't really used and the DW3 units on the DVTs were left isolated. This was to ensure a consistent feel of the brake - saving the driver having to recall if there was a Class 90 or an 86/7 ten coaches behind him. 

[rodent279]

So as I understand it, from the above, the rheo brake on an 86/87 didn't work if operated from the DVT?

[DY444]

So as I understand it, from the above, the rheo brake on an 86/87 didn't work if operated from the DVT?

 

No the rheo did operate on an 86/87 when the train was driven from the DVT.  

Edited May 9, 2018 by DY444

[leopardml2341]

Thanks for the useful info

[Calimero]

The brake handle is similar to a normal air brake on any other loco but also electrically energises the tap changer, relay valves signal the amount of rheostatic braking in relation to air braking.

 

From the DVT or DBSO (Intercity days) the TDM controls the electrical signals to loco via the RCH cables.

[Supaned]

As Seraphim says , when 86s were used with DVT sets , the usual practise was to leave the DW3 brake control unit isolated when the DVT was being hauled , in effect this meant that it acted as any other item of hauled stock. If the DVT was leading then the DW3 had to be operated to activate the brake controller in the DVT cab.

 

One of the reasons for leaving it isolated when being hauled was that if the TDM de-configured (ie the two computers stopped talking to each other) , which did happen periodically , the DVT would automatically apply the train brakes and it's parking brake, which then obviously was a long walk back for the driver to go and sort out.

 

When Virgin used a hired-in class 90 and short DVT set for Manchester - Birmingham services in the early to mid 2000s , the DW3 was usually left in all the time to give a faster brake application rate as described by the OP - primarily because by that time drivers were more used to Voyager trains with their far better brakes.

 

As far as losing the Rheo brake through neutral sections , all that really happened was a snatch in the train as the rheo dropped out and the tread brakes engaged. TBH the air brakes on an 86 were not that good without the Rheo. If the Rheo did drop out whilst going through a neutral section , the tap changer would need to wind back before the driver could take power again.

[E3109]

When braking near a neutral section with an 86 or 2x86, I tend to release the auto brake momentarily when passing through it, partly to let the rheo do its job when required and partly to avoid the noisy brake block chorus.

 

What I do find annoying as a driver, is when the "blend" between rheo and auto is set up incorrectly, or has gone out of sync.

Also if one or more traction motors are isolated, you have no rheo full stop.

 

As mentioned earlier class 90s are able to maintain the rheo brake through a neutral section but TBH I tend to momentarily release the brake on Skodas too, probably through habit.

[leopardml2341]

I think that description is pretty good. I cannot remember if anything happened as a consequence of the brief loss of rheo when the loco passed through a neutral section.

 

 

Why would rheo brake be lost when passing through a neutral section, was it an interlock with the power handle?

[russ p]

When braking near a neutral section with an 86 or 2x86, I tend to release the auto brake momentarily when passing through it, partly to let the rheo do its job when required and partly to avoid the noisy brake block chorus.

What I do find annoying as a driver, is when the "blend" between rheo and auto is set up incorrectly, or has gone out of sync.

Also if one or more traction motors are isolated, you have no rheo full stop.

As mentioned earlier class 90s are able to maintain the rheo brake through a neutral section but TBH I tend to momentarily release the brake on Skodas too, probably through habit.

Odd when you have one motor isolated on a 90 you get rheo on one bogie and air on the one with the defective motor

[Supaned]

Why would rheo brake be lost when passing through a neutral section, was it an interlock with the power handle?

 

No , but passing through the neutral section opens the Air Blast Circuit Breaker on the loco roof (effectively the main circuit breaker) - thus the power circuit that the Rheo brakes work as part of is broken. Once the circuit is tripped , the tap changer automatically winds back to the off position too. 

[leopardml2341]

Why would rheo brake not be permitted in neutral sections?

 

Rheo brake surely dissipates the energy as heat in on board resistors (most usually the same resistors used in the traction circuit) so why would the vcb being opened (by the APC magnet?) or the auto tap changer being 'off' prevent rheo brake please?

[Edwin_m]

Something to do with needing the field coils to be energised to provide braking?  Or does the regenerated current sustain these too?

Edited May 14, 2018 by Edwin_m

[leopardml2341]

Something to do with needing the field coils to be energised to provide braking?  Or does the regenerated current sustain these too?

Depends on motor type, but I believe the traction motors on the 'ALx' locos are straight series wound motors rather than separately excited ones, so the regenerated current will (can) do what you suggest.

[seraphim]

The traction motors on the older AC locos are, as said, series motors - ie the field windings are in series with the armature. They depend on the OLE supply to provide field excitation - hence the loss of rheo when passing through a neutral. To answer a couple of previous questions, braking energy is dissipated in large resistor banks which are force-cooled. The energy being dissipated in these resistors is substantial, so the blower motors must be proven to be operating before rheo can happen. Failures in this area have accounted for a good number of AC loco fires.

It is worth noting that the power density of an AC loco can be quite scary; the one-hour rating of a single Class 90 traction motor is greater than the output of an HST power car. Get the cooling wrong and expect to call the fire brigade.

The roof circuit breaker can be opened with the tap changer in any position, but opening it on-load is bad, as it will burn the contacts; hence (as commented above) drivers are expected to run-back the loco approaching a neutral.

Class 90 are SEPEX motors, so the fields are fed seperately from the armatures. This is largely a wheelslip control thing, and became the in-thing after trials on a Class 58 in the 1980s. 

If memory serves, when a loco is in Rheo, the output from the motors is connected in series. On older locos, this meant no rheo with a motor out. Class 86 & 87 on WCML expresses would eat brake blocks at a phenomenal rate in such circumstances, and would be diagrammed for a nightly block check. 

Never worked on Class 91, funny Eastern Region things.

[leopardml2341]

They depend on the OLE supply to provide field excitation - hence the loss of rheo when passing through a neutral.

Thanks Seraphim, that fills in the missing bit

[45125]

The traction motors on the older AC locos are, as said, series motors - ie the field windings are in series with the armature. They depend on the OLE supply to provide field excitation - hence the loss of rheo when passing through a neutral. To answer a couple of previous questions, braking energy is dissipated in large resistor banks which are force-cooled. The energy being dissipated in these resistors is substantial, so the blower motors must be proven to be operating before rheo can happen. Failures in this area have accounted for a good number of AC loco fires.

It is worth noting that the power density of an AC loco can be quite scary; the one-hour rating of a single Class 90 traction motor is greater than the output of an HST power car. Get the cooling wrong and expect to call the fire brigade.

The roof circuit breaker can be opened with the tap changer in any position, but opening it on-load is bad, as it will burn the contacts; hence (as commented above) drivers are expected to run-back the loco approaching a neutral.

Class 90 are SEPEX motors, so the fields are fed seperately from the armatures. This is largely a wheelslip control thing, and became the in-thing after trials on a Class 58 in the 1980s. 

If memory serves, when a loco is in Rheo, the output from the motors is connected in series. On older locos, this meant no rheo with a motor out. Class 86 & 87 on WCML expresses would eat brake blocks at a phenomenal rate in such circumstances, and would be diagrammed for a nightly block check. 

Never worked on Class 91, funny Eastern Region things.

 

91s rheo works just the same as a Skoda.

[russ p]

Going a bit off topic what is the discis or whatever it is system was that is permanently isolated was?

[seraphim]

OK, you got me. DISC = Drivers's Indicated Speed Control. Essentially cruise control - driver sets a speed, loco accelerates to and sits at the speed. It was isolated in DVTs on West Coast because it was suspected of causing tapchangers to hunt around notches on Class 86 & 87. I THINK it was re-instated on Anglia when it became 100% Class 90, but can't recall.

[russ p]

Thats the automatic speed limiter or ASL that still works on the 90 and DVTs

This other system is called DISCIS I was told its some kind of wheel slip system but no one seems to know

The isolation switch is next to the AWS one