Meridians and Wheel-flats

[222001]

Is it just me or has anyone else noticed that Meridians seem to get a lot of wheel flats compared to Voyagers and the EMT HSTs. Almost every 7 car Meridian always seems to have a wheel flat. 222001 at the weekend had 3 wheel flats one of which sounded really bad.
Most of the wheel flats are on the front wheels leading cars which must get really annoying for the driver.

Can anybody think why this is?

This must also cost a lot of Meridians being in service.

 

[91101]

Is it a recent issue?

It'll be due to leaffall, and wheels slipping, causing friction and wearing the wheel profile down. The leading wheels will be the worst as the rear wheels will be able to grip the rail better.

 

[222001]

Is it a recent issue?

It'll be due to leaffall, and wheels slipping, causing friction and wearing the wheel profile down. The leading wheels will be the worst as the rear wheels will be able to grip the rail better.

It seems to be all year round. But it has got worse recently. But why do Meridians get more than HSTs or Voyagers. Is it down to the routes they operate? With the Meridians compared to HSTs I suppose it could be down to that they have more power to put down so are more likely to slip.

Edit: I remember around April/May time EMT mentioned that the Meridians were showing poor performance due to wheel-flats on one of their performance posters at stations and that the were giving them tougher maintainance. Could it be a fleet problem?

 

[class 313]

Slipping wouldn't cause a wheel flat would it? Its mote to do with the brakes locking the wheel. Or that's what I thought.

 

[P156KWJ]

not been overley noticeable but they do seem to have wheelflats a lot

 

[CosherB]

323s are another type that suffers lots of wheel flats. They are our local Northern Rail train on the Manchester Crewe line, and every set seems to have a few flats. The standard sound these units make always includes the rapid bang-bang-bang-bang of at least one flat.

Why is that? Don't they have ABS to prevent wheel-locking under braking?

CS

 

[TheSlash]

Slipping can turn out a wheel flat, but it often causes defects in the rail and the wheelset due to the localised heating created by the speed of the slip.

It always amazes me that when you go on a WSP course, you are led to believe a wheel should never slip or slide because the WSP should predict it and take preventative action

 

[CosherB]

It always amazes me that when you go on a WSP course, you are led to believe a wheel should never slip or slide because the WSP should predict it and take preventative action

Is WSP the rail equivalent of Anti lock Brake System (ABS) on cars? I.e. it releases the brake if the wheel is about to lock.

If so, do you ask the WSP course instructor why wheel flats still happen with WSP-equipped trains?

CS

 

[mbonwick]

I thought it just stuck sand down.......

AFAIK, the rail industry doesn't really have an alturnative to ABS.

 

[222001]

I just think it's strange that Meridians get a lot more wheelflats than Voyagers do. What could it be as they are practically the same train and the Voyagers cover a lot more distance.

 

[TheSlash]

Is WSP the rail equivalent of Anti lock Brake System (ABS) on cars? I.e. it releases the brake if the wheel is about to lock.

If so, do you ask the WSP course instructor why wheel flats still happen with WSP-equipped trains?

CS

Wheel Slip/Slide protection. The idea is the system takes constant speed readings from a vehicle's axles and compares them to what should be happening. It then pre empts a wheelset lock by releasing and re applying the brake with lesser force.
I think the flats occure during the split second that it takes to calculate the data
--- old post above --- --- new post below ---
More and more Transits are appearing with switchable traction control, but even with the TC switched on, i can still get one wheel spinning nicely

 

[adc82140]

I was on an FGW HST on Thursday morning that had the most horrendous flat- it sounded like there was an underfloor engine it was so bad- one of the commuters even commented that he though the train had square wheels.

 

[class 313]

Meridians slip so much in the rain that its quite funny when trying to leave as you feel the slipping.

 

[O L Leigh]

It always amazes me that when you go on a WSP course, you are led to believe a wheel should never slip or slide because the WSP should predict it and take preventative action

Then the instructor doesn't have a complete grasp on how WSP works. No system can predict a slip or slide and prevent it from happening; it can only react to it when one happens.

Generally what happens is that it is the leading wheelset that will start to slide first. The WSP will kick in and attempt to keep the wheelset turning but, if it's operating for more than a certain amount of time, it will give up and allow the wheelset to lock. This is a design feature of the system. The idea is that the locked wheelset will slide along the railhead, scrape off any contaminants and "condition" the railhead so that the following wheelsets will have better grip. This is the reason why the sanders are fitted ahead of the second bogie and not under the leading one, as it would negate this benefit.

Of course, if the railhead conditions are sufficiently bad the WSP may allow more than just the leading wheelset to lock which can cause flats elsewhere along the train. You can also get flats under any coach if the WSP is faulty and does not intervene quickly enough to prevent a lock-up.

The other thing to bear in mind is that WSP is not a very fast system because it uses air. ABS on a car will pulse the brakes many more times per second than WSP is capable of. Also, from watching the speedo's behaviour when you get a WSP intervention, it would appear to allow a much wider range of wheel speeds relative to the train's actual speed before activating.

O L Leigh

 

[CosherB]

Thanks, OLL. Very informative post. I understand what's going on a lot better now.

CS

 

[222001]

Yes that post explained it very well. I now understand why it is mainly the front wheels of the Meridians that have the flats.

I found a video of 222001 two wheel flats one of which sounds very bad! - http://uk.youtube.com/watch?v=CZUFq6ZQevQ

 

[westcoaster]

also when the wheel gets a flat, iirc the flat spot will nearly always be where the wheel locks up in relation to the rail thus making the flat bigger.
also if you get a lot of wsp activity and it continues for about a minute, and you are still slipping along you may cause the low main air govenor to kick in and lock up all the wheels.

 

[Siggi155]

It's a well-known problem of all disk-braking vehiles, some more, some less. Leaffall and mud causing a slippery film on the wheel's running surface and the electronic WSP is not fast enough to prevent from blocking while breaking. Here in germany they had huge problems with the whole range of new intruduced city train EMU's every year in autumn. There were too many signal overruns and platform passings.
So someone reminded the old brake block system and invented a "cleaning brake". When the brake is applied, a cleaning shoe moves and presses the block against the wheels at a small pessure. So it cleans the surface from mud, squished leaves and all the things causing a slippery film on it. That effectively solved the problem. And some types of goods train electric locos were also equipped with the same system.

 

[TheSlash]

Here we go again, O L Leigh talking technical :roll:

The WSP works by taking a speed reading from a probe on each of the 4 axles on a vehicle. These readings are fed into the WSP and compared. Any axle travelling 4mph slower than the rest is deemed as about to lock up, so the brakes are released and re applied.
A situation could arise where all 4 axles lock up at the sametime. This could fool the WSP into thinking that the vehicle was stationary, when in fact it was sliding.
To combat this, early versions of the WSP used to a Capacitor discharge to simulate the braking curve of a 5th axle. This was then used as a Datum to compare the 4 axles against.
More recent versions feed the values of the 4 real axles into a computer, which compares them against braking curve graphs to determine if the axles are declerating at the correct rate.

My instructor worked for the Brakes performance department at Selhurst, O L Leigh, i'll pass on your kind sentiments about his knowledge.
--- old post above --- --- new post below ---
A wheel set will always lock on a flat spot because of the increased forced needed to rotate two flat surfaces. The harder you brake, the more energy is needed for the flat spot to rotate away from the rail head, if that energy isn't available, then the flat surface will just skim along the rail head.

I'll get some pictures of Wheelburns, Squats and Skid Marks and post them up.
--- old post above --- --- new post below ---

So someone reminded the old brake block system and invented a "cleaning brake". When the brake is applied, a cleaning shoe moves and presses the block against the wheels at a small pessure. So it cleans the surface from mud, squished leaves and all the things causing a slippery film on it. That effectively solved the problem. And some types of goods train electric locos were also equipped with the same system.

That technology has been in use for years over here, called a scrubbing block. Not only does it clean the tyre for increased traction, but it reduces electrical resistance between the tyre and the railhead, making it easier for the wheels to operate the track circuit.

 

[O L Leigh]

Thank you, Slash.

I'm sorry if my technical explanations are too taxing. I felt that it was merited given the direction that the discussion was taking. If you'd rather I didn't bother then perhaps you should just say, or are you concerned that I'm undermining you.

I believe that, as with many things, the theory and practice do not always marry up. I certainly intended no offence, so perhaps you failed to accurately represent the information you were trying to get across which caused me to draw an inaccurate (though not incorrect) conclusion. The suggestion you made was that your instructor teaches that WSP means that a wheel should never slip or slide, but we both know from practical experience that this is patently not the case. So he's either taught you only the theory of the system but failed to explain how it works in practice or you've failed to give him the proper credit, because WSP actually permits a full-on slide with at least one wheelset when things get really hairy.

I'm sorry if this appears to be a rant as it isn't intended as such. I am a bit miffed that you seem set on disagreeing with me over this and other topics, but I'm not mad at you because of it. The information that between us we have posted is correct and not contradictory. The only difference is in our perspective. You fix them (or so I gather, so forgive me if I've got that wrong) while I drive them. I don't understand the componentry that makes up the WSP system, but I do know what it does, doesn't, should and shouldn't do operationally. I've zero'd speedos and had them waving up and down all over the place while waiting for the unit to decide whether or not it's going to go into a proper slide and what it's going to do about it.

To pick up some other points:

It is at least theoretically possible for WSP activity to blow an LMAG and cause an emergency brake application, but it is not likely. When the air gets low the compressor will run automatically to top up the main air. You'd need a LOT of WSP on a healthy unit to be tripped up by low main air. However, it becomes a serious possibility where you only have one operational compressor between two units.

The use of secondary brake tread "scrubbers" is interesting but doesn't deal with the gunk on the railhead. What is the continental solution to railhead contamination?

In the UK the trick is to reduce the build-up of contaminants on the wheel treads by removing them from the railhead using high pressure water jets. This means you get a comparatively clean interface between the rail and the wheel. In conjunction with other measures like vegetation clearance, it works quite well. You can brake almost normally at most locations and still run to time even during the peak leaf-fall season. Just scrubbing up the treads doesn't deal with the contaminants on the rail itself. If the railhead is treated the same on the Continent as it is here in the UK my view would be that the tread scrubbers are probably redundant and wouldn't be of huge benefit.

Would be interested to hear more about that, though.

O L Leigh

 

[valentaman]

the reason the 222's have wheelflats is the severe amount of curves put the units wheels under alot of pressure and 1 unit is away permanently for tyre turning

222003 at the moment!

main problem being market harborough curve and kettering and syston curve dont help!

hope this helps

 

[class 313]

the reason the 222's have wheelflats is the severe amount of curves put the units wheels under alot of pressure and 1 unit is away permanently for tyre turning

222003 at the moment!

main problem being market harborough curve and kettering and syston curve dont help!

hope this helps

But Voyagers also have to go along similar curves and more of them, also Luton Airport Parkway there's a nice S bend which is pretty severe.

 

[222001]

the reason the 222's have wheelflats is the severe amount of curves put the units wheels under alot of pressure and 1 unit is away permanently for tyre turning

222003 at the moment!

main problem being market harborough curve and kettering and syston curve dont help!

hope this helps

Thanks, now I see why Meridians get them more than some other units. No wonder I seen a 7 car Meridian diagram HST subbed if one is away for tyre turning! Hope they don't have to do it too often on the new timetable as 6/7 Meridians are required in service everyday for the Sheffield diagrams which need to be Meridians or they will loose time (apparently)!

On another note I have noticed that the amount of engines working on the 7 car Meridians has improved recently I think. The past few 7 cars I've seen all engines have been working, compared to 4 out of 7 on a few I've seen in the past!
--- old post above --- --- new post below ---

But Voyagers also have to go along similar curves and more of them, also Luton Airport Parkway there's a nice S bend which is pretty severe.

It could be the way the track is built on the MML? Saying that not many HSTs seem to get them.

 

[class 313]

On another note I have noticed that the amount of engines working on the 7 car Meridians has improved recently I think. The past few 7 cars I've seen all engines have been working, compared to 4 out of 7 on a few I've seen in the past!

Having all 7 engines on is a huge waste of resources as they don't add much to the performance. Hence you would never see all 9 engines on when they were 9 car.

 

[222001]

Having all 7 engines on is a huge waste of resources as they don't add much to the performance. Hence you would never see all 9 engines on when they were 9 car.

I agree its wastefull, especially with a 10 car Meridian - I'm sure I seen one of these with all engines running too. Imagine how much fuel that takes!

 

[class 313]

I agree its wastefull, especially with a 10 car Meridian - I'm sure I seen one of these with all engines running too. Imagine how much fuel that takes!

Exactly that's why it was/is rare to see all the engines running. Though all the cars having engines is a good idea, because when they shuffle sets they don't have to worry about trailers and the such.

 

[CosherB]

Well I'm glad OLL did get technical! As a non-railwayman I didn't understand quite a lot about train brakes until his post. Please keep posting techy posts, OLL - and anyone else who has the knowledge and can put it across as he can.

 

[MCR247]

Havent they always had these, because i have always heard this sounds on 220/1/2

 

[class 313]

Havent they always had these, because i have always heard this sounds on 220/1/2

Most if not all trains have them at some point.

 

[TheSlash]

The MPVs are good at cleaning the railheads, but a nightmare for track maintenance.
Blasting high pressure water at steel is never going to come out well. Also they put down some kind of sand in the mixture now, which makes Rolling Contact Fatigue inspections a nightmare, both visually and ultrasonically.

O L Leigh, you are the one that likes to come in making the 'factual' technical statements, i just come along and correct the facts for the good of man kind, sometimes correcting your posts can be quite taxing due to the levels of inaccuracies.
I believe i've met your clone, he tried to tell me it was perfectly acceptable to run trains over bullhead rails with no keys in and totally rotten sleepers.

Regards

Slash

TRKIND, LKT, COSS {CRP}, HSM, BDN, Stress level 1, various TRKs, Small Plant Operator, SCC, MT162, etc etc