Sounds Like a Flat...

[O L Leigh]

...but isn't.

There's a section of route I cover regularly that appears to have started exhibiting a strange phenomenon. Driving along that route you would swear that the train has a wheel flat with the telltale banging and even an accompanying vibration through the floor. It happens every trip and seems to affect every unit, but I know that it's not a wheel flat because it starts at a certain location, runs for several miles on curves as well as straights, and then disappears.

I was wondering whether or not any other driver has encountered this and would know what it might be. I'm assuming that if it's not the train it must be the track. But what could cause it? Is it to due with rail grinding or could it be something else?

O L Leigh

 

[321446]

Could it have been caused by a bad flat on another unit/freight damaging the railhead? I admit it would have to be one hell of a flat, but it's all I can think of, particularly as it has manifested itself in a way that the regular symptoms sound like a flat.

One thing I've noticed is sometimes I pick up a flat that runs for a short while then clears. I've put it down to a bit of contamination on the wheel, but I'll take more notice now as it may be happening in the same place like yours.

Curiouser and curiouser said Alice.

 

[wheel tapper]

could it be that the rail head has lost it profile and is need of grinding and the unit is hunting maybe

 

[DownSouth]

I've seen/felt/heard something that sounds like it might be similar in Adelaide, South Australia.

Up to the start of last year, one of the two lines I use at times was served by some old DMUs getting near retirement age which are prone to bad wheel flats, and some modern DEMUs from the mid 1990's which use mostly dynamic braking and are not. It was common to feel these 'false flats' when riding through the acceleration zone leaving stations on a DEMU, but which would mostly disappear in cruising areas and completely disappear in braking zones. The intervals were completely wrong for the smaller wheel size on the newer DEMUs.

After the line was subject to a full track rebuild and electrification, the old DMUs were banned from service on that line due to their raised driver's cab (with a fibreglass roof!) being unsafe for use under the wires. Coincidentally, the 'false flat' sensations are also now completely absent on both the modern DEMUs (still seeing limited service until all the EMUs are delivered) and the brand new EMUs.

I put it down to the rails being hammered by the squared off wheels on the old DMUs.

It's worth noting that the other route I use has not seen any of the old DMUs for about 10 years (because a DEMU is far better for climbing long 2.3% grades) and after the 2009 track upgrades it doesn't have any of the 'false flat' sensations either.

 

[455driver]

could it be that the rail head has lost it profile and is need of grinding and the unit is hunting maybe

That was my guess as well.

Oh and a wheel flat wont normally be over the entire tread width of the wheel either so it could be, for example, that it bumps on the straight and left hand bits of track but not on right handers because that part of the tyre isnt damaged.

 

[Bald Rick]

Almost certainly rail corrugation. I would be surprised if the local track maintenance engineer didn't know, but it wouldn't do any harm to report it via your DM to pass on to Network Rail.

 

[O L Leigh]

One thing I've noticed is sometimes I pick up a flat that runs for a short while then clears. I've put it down to a bit of contamination on the wheel, but I'll take more notice now as it may be happening in the same place like yours.

Oh and a wheel flat wont normally be over the entire tread width of the wheel either so it could be, for example, that it bumps on the straight and left hand bits of track but not on right handers because that part of the tyre isnt damaged.

Both of these options I had already considered. However, I have discounted them both on the basis that the affected section is a not insignificant number of miles (potentially as many as 20-25 miles) which would rule out contamination, and covers straights and curves in both directions which would also rule out localised tyre damage. It is the suddenness with which it disappears and the fact that it does not occur elsewhere on lines with similar characteristics I find curious.

could it be that the rail head has lost it profile and is need of grinding and the unit is hunting maybe

I was wondering whether it could have been that the rail had been incorrectly ground.

Almost certainly rail corrugation. I would be surprised if the local track maintenance engineer didn't know, but it wouldn't do any harm to report it via your DM to pass on to Network Rail.

I did mention it to a gaffer today and he looked equally baffled. I might have to take one out for a little spin tomorrow.

Anyway, thanks for all the answers so far.

**EDIT**

On the subject of hunting, I was always of the impression that this was a high speed phenomenon. The sounds I've been hearing have been happening at all speeds, even when braking to a stop.

O L Leigh

 

[TDK]

Both of these options I had already considered. However, I have discounted them both on the basis that the affected section is a not insignificant number of miles (potentially as many as 20-25 miles) which would rule out contamination, and covers straights and curves in both directions which would also rule out localised tyre damage. It is the suddenness with which it disappears and the fact that it does not occur elsewhere on lines with similar characteristics I find curious.



I was wondering whether it could have been that the rail had been incorrectly ground.



I did mention it to a gaffer today and he looked equally baffled. I might have to take one out for a little spin tomorrow.

Anyway, thanks for all the answers so far.

**EDIT**

On the subject of hunting, I was always of the impression that this was a high speed phenomenon. The sounds I've been hearing have been happening at all speeds, even when braking to a stop.

O L Leigh

Jointed track? Only joking Mr Leigh. There was a section on the North Wales coast where it seemed that the wheels had picked up something but you would only get the sound when in a 158, nothing on a 175. It disappeared as quick as it came, was like it for about 2 weeks and then it just went!