Hot Axle Box Detectors

[Western 52]

I have some questions about HABDs:-
Are there specific criteria regarding where they are placed?
Are they integrated with the signalling system?
Are they effective with inside frame bogies, where the axle box is behind the wheel?

 

[Supercoss]

It was mileage related when most first installed with further restrictions if two adjacent were defective in same direction of travel .
No integrated to interlocking, sounds an audible alarm and generates display or print out, don’t forget to count axles including loco
Some more modern stock has in built hot acre box detectors with inside frame gobies

 

[Annetts key]

Are there specific criteria regarding where they are placed?

Yes, by distance. HABD sites are located so that trains pass over one within a defined distance. Just don't ask me for the number!

Are they integrated with the signalling system?

It depends on the signalling system, the type of HABD equipment and the requirements at the time. The HABD equipment itself is not classed as signalling equipment. Although it's the S&T who install, maintain and fault find it.

The following is former BR WR practice for Panel signal boxes (PSBs). Modems are provided to transmit the data from the site equipment (which is not connected to the signalling system at all) to the PSB. At the PSB in the equipment room, the receiving modem is located (typically in a 19 inch rack cabinet) along with any required power supply equipment (which is powered from the signalling 110V AC power system). The modem output feeds along a cable to the HABD equipment cabinet (normally located on the signal box operating floor). The HABD equipment has an alarm output. This goes back to the signalling equipment room where it goes into an interface box (that contains various relays) or to individual relays.

When the HABD equipment detects a hot axle or a fault is detected (loss of incoming modem signal, integrity error etc.) It signals to the appropriate relay. this is wired as a latch circuit. This then causes a sounder to 'alarm' on the signallers panel. Often a light illuminates as well. The signaller has to push the button corresponding with the alarm/light to acknowledge the alarm. Some older systems also take an output from the relevant track circuit (at the signal box) and feed this to the HABD equipment to reset the axle counter signal box equipment as a train approaches.

Are they effective with inside frame bogies, where the axle box is behind the wheel?

I don't know much about rolling stock. So this may not answer your question. But the HABD sensor (called the scanner) is located on the four foot side of the rail (one for each rail) and scans the rear of the axle box (at an angle) as the train passes over it (assuming the train is travelling in the normal direction of travel). The scanner is not aimed at the wheel and is not obstructed by the wheel. There is a standard that defines the alignment and field of view of the scanner. The scanner itself is an infrared sensor which only receives radiated IR light. Separate wheel flange sensors tell the HABD equipment when an axle should be in view so that sunlight and other heat sources can be ignored.

For rolling stock where the lineside equipment is not suitable, that stock should have it's own axle box sensors.

 

[Belperpete]

One of the things the detector measures is the difference in temperature between opposite wheels, so it used to be the case that they weren't put close after a sharp bend , or somewhere where a train might have run a significant distance with the sun full on one side. Likewise they were not put immediately after a significant speed restriction, where trains were likely to have braked heavily.

Somewhere where there was a suitable siding or somewhere to put a train that had been alarmed, so that it wasn't stopped blocking the line, was also a consideration.

 

[Western 52]

Thank you both for your amazing replies, I've learned a lot about HABDs from them and didn't realise there was so much to them. I also didn't know some vehicles have detection built in, but that certainly makes sense.

One final question - is there a particular temperature that would activate the sensors or is it based mainly on temperature differences between axle boxes?

 

[172007]

Class 172's have FlexEco bogies sane as I believe in class 220 and 222. Not 221.

The class 172 bogie will not set HABD off. They are inside roller bearings. They have a fusible plug bolt that once a certain temperature is exceeded melts and dumps the air out of the train, causes an emergency brake application and a Hot Axle warning light in the cab.

 

[Annetts key]

Depending on the type of HABD equipment, there are typically three trigger points.
All have:
Absolute temperature for each axle box,
Differential temperature between the left and right axle box on the same axle.

Later computer based systems (now the current standard) also have:
Differential temperature between an axle box and the average of the whole train for either plain bearings or roller bearings.
IIRC it’s the average for each vehicle that determines if the HABD decides which bearings a vehicle has.
These have some data stored so that they can work out the type of train. I don’t know how detailed this information is. I do know that steam trains and engineering vehicles (machines etc.) do rather confuse them.

Note that the temperatures on the systems I have the most experience with (made by Servo) are not calibrated in degrees C (a different system is used), and I have long forgotten how to do the conversion.

 

[Boilinthebag]

Are there specific criteria regarding where they are placed?

Yes, by distance. HABD sites are located so that trains pass over one within a defined distance. Just don't ask me for the number

Following an HABD activation where no fault is found with the relevant axles, trains can proceed but must pass over /be checked by another HABD within fifty miles. A second activation with no fault found means proceeding at a reduced speed. I think these rules lie within company specific instructions so may vary. In terms of location, they are in my experience far enough ahead of a suitable location to recess the train, bearing in mind the time taken for the alarm to be acknowledged and the train to be bought it a stand.

 

[gingertom]

Following an HABD activation where no fault is found with the relevant axles, trains can proceed but must pass over /be checked by another HABD within fifty miles. A second activation with no fault found means proceeding at a reduced speed. I think these rules lie within company specific instructions so may vary. In terms of location, they are in my experience far enough ahead of a suitable location to recess the train, bearing in mind the time taken for the alarm to be acknowledged and the train to be bought it a stand.

May I ask what's the procedure when a hot axle event is detected? The last thing anyone wants is for the thing to seize solid, with the consequential damage and disruption that could cause.

 

[Annetts key]

May I ask what's the procedure when a hot axle event is detected? The last thing anyone wants is for the thing to seize solid, with the consequential damage and disruption that could cause.

This is my understanding, I would be glad if others can add detail or corrections.

When a lineside HABD system alarms, the signaller will bring the train to a stand at a suitable signal as soon as practical. They will explain the reason to the driver. The driver will then check the train for problems. If the driver confirms that there is a problem, the train will proceed at much reduced speed until there is a suitable siding or a loop where either the whole train or just the defective vehicle can be stabled. The unaffected part of the train can continue. The defective vehicle will require fitters to attend and examine it before it can be moved.

Sometimes the problem is that of a brake being on/dragging causing the wheel to heat up. The heat then conducting to the axle box. If the problem with the brake can be dealt with (maybe it can be isolated) then the train may be able to continue to a suitable maintenance depot or to its destination. Often at reduced speed.

 

[Belperpete]

Later computer based systems (now the current standard) also have:
Differential temperature between an axle box and the average of the whole train for either plain bearings or roller bearings.
IIRC it’s the average for each vehicle that determines if the HABD decides which bearings a vehicle has.
These have some data stored so that they can work out the type of train. I don’t know how detailed this information is. I do know that steam trains and engineering vehicles (machines etc.) do rather confuse them.

If they think it is a loco-hauled train, I think they can also ignore the loco, on the basis that a loco's axles are likely to be heated by the motors.

 

[MadMac]

I was in Edinburgh SC one day when Newbiggin HABD alarmed with axle 42 shown: it was dismissed due to the train concerned being a three car DMU! Apparently the exhausts were known to occasionally cause spurious activations…..

 

[Annetts key]

I was in Edinburgh SC one day when Newbiggin HABD alarmed with axle 42 shown: it was dismissed due to the train concerned being a three car DMU! Apparently the exhausts were known to occasionally cause spurious activations…..

Yes, certain classes of DMU are supposed to be fitted with heat shields to prevent their exhaust system interfering with the HABD scanners. But for whatever reason, it's not effective on some units.

 

[Pigeon]

Sometimes the problem is that of a brake being on/dragging causing the wheel to heat up. The heat then conducting to the axle box. If the problem with the brake can be dealt with (maybe it can be isolated) then the train may be able to continue to a suitable maintenance depot or to its destination. Often at reduced speed.

They have specific detectors for hot wheels caused by eg. dragging brakes in addition to those for hot axleboxes. I think some of them are separate units, while some of them are combined with a hot axlebox detector in the form of a single IR-detector unit with two "windows", one looking at the wheels and one looking at the axleboxes. I seem to remember a diagram, probably in the accident report for the seized-brake derailment in South Wales near Llanelli, which showed what parts of the assembly such a detector would look at. I also seem to remember that there are not so many hot wheel detectors as hot axlebox detectors.

 

[Annetts key]

They have specific detectors for hot wheels caused by eg. dragging brakes in addition to those for hot axleboxes. I think some of them are separate units, while some of them are combined with a hot axlebox detector in the form of a single IR-detector unit with two "windows", one looking at the wheels and one looking at the axleboxes. I seem to remember a diagram, probably in the accident report for the seized-brake derailment in South Wales near Llanelli, which showed what parts of the assembly such a detector would look at. I also seem to remember that there are not so many hot wheel detectors as hot axlebox detectors.

Yes, some designs of HABD can also detect the wheel temperature in order to detect wheel or brake problems. The sensor may be in the same enclosure but is separate from the axle box sensor, as it needs to scan at a different angle.

The question in the OP was about HABD systems rather than systems that are specifically designed to detect wheel or brake problems. I only mentioned brakes as this is sometimes the cause of a HABD activation where it’s the elevated axle box temperature that has been detected.

The wheel temperature facility was not included on any of the HABD installations that I worked on. At the time there was no requirement for this facility at these sites.

It is possible that elsewhere there are installations that have been provided with wheel temperature sensor systems.

 

[D6130]

When I was a driver at Skipton, the HABD on the Down West Coast Main Line at Hest Bank was rather prone to being activated by hot water running out of the toilet sink drain pipe on class 156 units. On several occasions I was routed into one of the loops at Carnforth to examine my train - with the consequential delay caused - and it was subsequently established by the conductor that someone had been washing their hands in just the wrong place!

 

[Towers]

Class 172's have FlexEco bogies sane as I believe in class 220 and 222. Not 221.

The class 172 bogie will not set HABD off. They are inside roller bearings. They have a fusible plug bolt that once a certain temperature is exceeded melts and dumps the air out of the train, causes an emergency brake application and a Hot Axle warning light in the cab.

That’s an interesting design! How does the driver reset the air in order to move the thing, presumably a bogie/brake isolation is required?

 

[172007]

That’s an interesting design! How does the driver reset the air in order to move the thing, presumably a bogie/brake isolation is required?

Air isolation cock to stop the leak. Then it's a new fusible plug if that's failed or, most probably, wheel skates.