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Tread brakes

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Bletchleyite

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By pushing a pad made of friction material against the tread (running surface) of the wheel, as distinct to disc brakes which do so against a brake disc bolted to the wheel.
 

Ken H

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so all sprinters up to class 156 have tread brakes
all after have disk braking

not so sure about EMU's Do 317's have disks?
 

edwin_m

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All EMUs have discs from at least class 313 onwards. I think some of the older AC units did too, but pretty sure the DC slam-door units didn't.
 

hexagon789

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All EMUs have discs from at least class 313 onwards. I think some of the older AC units did too, but pretty sure the DC slam-door units didn't.

310 had disc brakes and WSP, not sure if the 312s did as well. The 100mph-rated 309s were tread-braked.
 

Domh245

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As I believe all the new aventuras aswell?.

No, Aventras have disk brakes, although the 345s have the first/last axle of the train with a different arrangement, seeminly with inboard disks (as opposed to wheel mounted). Also worth noting that it is only the motored bogies of the 700s which are tread braked, the unpowered bogies have inboard disks
 

Shimbleshanks

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Do tread brakes have any advantage over discs when there is leaf slime or other stuff leading to low adhesion? Does the tread brake have a cleaning action on the wheel surface?
 

Bald Rick

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Do tread brakes have any advantage over discs when there is leaf slime or other stuff leading to low adhesion? Does the tread brake have a cleaning action on the wheel surface?

Very much so. But they are less good at actually braking than disc brakes.
 

hexagon789

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Do tread brakes have any advantage over discs when there is leaf slime or other stuff leading to low adhesion? Does the tread brake have a cleaning action on the wheel surface?

Yes, they do clean the wheels, but disc brakes provide a higher more consistent level of braking particularly at higher speeds.

In poor rail conditions while the tread brakes may be less inclined to lock-up the wheels, the disc brake will always at least match if not still exceed the braking performance of the tread brake.
 

furnessvale

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Yes, they do clean the wheels, but disc brakes provide a higher more consistent level of braking particularly at higher speeds.

In poor rail conditions while the tread brakes may be less inclined to lock-up the wheels, the disc brake will always at least match if not still exceed the braking performance of the tread brake.
Not sure about the last sentence.

IMO, the best compromise is disc braking with tread conditioning blocks operating at, say 10psi.
 

hexagon789

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Not sure about the last sentence.

If your maximum braking rate is 9%g with disc brakes and 7%g with tread but railhead conditions are so poor that a brake rate of say only 1%g can be supported then you will get 1%g deceleration with either type of brake. Modern WSP-equipment will typically give the disc-brake the edge even in poor conditions.

That's how I understand it anyway.
 

TheEdge

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I think now with the improvement of disc brakes and WSP the advantages of tread brakes in low adhesion is mostly a thing of the past.

I believe the only time now tread brakes still trump anything else in low adhesion is where stock has tread and rheostatic or regenerative braking, as those really can be appalling in poor conditions. I know on black adhesion days (and sometimes successive red ones) the AGA Class 90 will have their rheostatic brakes isolated so the tread brakes's cleaning effect help with keeping wheels clear of contamination.
 

edwin_m

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Only on the driven wheels I think. Definitely not all wheels though.
Yes, I believe they couldn't find room for the disc brakes on the powered axles. Something like a 700 will use a lot of electric braking, so the friction brakes get an easier life although they still have to be specified for the full braking load in case of a failure in the electrics.
 

ComUtoR

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Only on the driven wheels I think. Definitely not all wheels though.

Yes, I believe they couldn't find room for the disc brakes on the powered axles. Something like a 700 will use a lot of electric braking, so the friction brakes get an easier life although they still have to be specified for the full braking load in case of a failure in the electrics.

From what I was told, nothing I can confirm, is that the tread brakes only kick in at low speed and emergency and are used to hold the train rather than brake. You can certainly feel a difference when a unit will change from the rheo/regen to friction. Less obvious on a 700 compared to a 376.
 

dk1

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From what I gather the new 745/755 fleet from Stadler have disc brakes but also a form of brush to clear the wheel itself preventing the build up of leaf mulch.
 

CC 72100

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From what I gather the new 745/755 fleet from Stadler have disc brakes but also a form of brush to clear the wheel itself preventing the build up of leaf mulch.

Scrubber blocks?

Designed to make up for the fact that disc braked trains when braking don't clean the wheels in the same way that tread brakes trains do.
 

dk1

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Scrubber blocks?

Designed to make up for the fact that disc braked trains when braking don't clean the wheels in the same way that tread brakes trains do.
Most likely. Not been on the course yet so only getting hear say.
 

furnessvale

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If your maximum braking rate is 9%g with disc brakes and 7%g with tread but railhead conditions are so poor that a brake rate of say only 1%g can be supported then you will get 1%g deceleration with either type of brake. Modern WSP-equipment will typically give the disc-brake the edge even in poor conditions.

That's how I understand it anyway.
I understand that, but does it take into account poor TREAD condition, which scrubbing blocks can eliminate, rather than dirty rails?
 

hexagon789

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I understand that, but does it take into account poor TREAD condition, which scrubbing blocks can eliminate, rather than dirty rails?

WSP does work to condition the rails on disc-braked trains, but yes tread brakes are definitely better at getting rid of all that leafy muck, I can't deny that ;)
 

Ken H

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What happened to network South Easts leaf fall train, the 'Swedish Scrubber'? Is it still working? It had wire brushes and squgees to clean the railhead.

Didnt Thameslink have a converted MLV that did sandtite but would work as a DVT in a Class 319 formation?
 

TRAX

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Is that even allowed? Does it not have an inboard axle-mounted disc brake then?

I don’t know if this is the reason on the 345, but a lot of trains have unbraked end axles because these are the two axles which enable the speed to be measured.
 

LOL The Irony

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Do tread brakes have any advantage over discs when there is leaf slime or other stuff leading to low adhesion? Does the tread brake have a cleaning action on the wheel surface?
Yes. I believe that 158's are fitted with discs and treads. (the treads were retrofitted later after their first autumn in Yorkshire resulted in 156 158 hybrid sets being formed.)
 
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