Flexity Strip track circuits

Vindaloo 42

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Do lines relaid with Continuous Welded Rail (CWR) still require flexity strips between the track circuit gaps?
 
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I assume they are talking about the continuity bonds found across fishplate joints on jointed track?
 

civ-eng-jim

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Ah.

I know for renewals on points the track panels bond holes are drilled at the rail ends but believe that's just for temporary phase where the track is clamped together before welding up the following week.
 

MarkyT

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Aimed at the Minor Railways Section, this IRSE document covers the traditional methods of track circuit bonding.

Where track circuits are used, some sort of bonding is always required along with insulated rail joints in turnouts and crossings, even where otherwise completely welded construction is employed. On plain line, welds are considered electrically perfect, requiring no bonding around them, although the extremities of track circuits will still need to be connected to the rails by cabling, even where 'jointless' products such as the TI.21 are used. Axle counters change this, however, as will other future train detection methods.
 

mcmad

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As Jim says other than the temporary pre weld situation there are no bonds across welds in S&C. There are 'pigtails' between the switch and stock and sometimes at the crossings if fab'd crossings.
 

MarkyT

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As Jim says other than the temporary pre weld situation there are no bonds across welds in S&C. There are 'pigtails' between the switch and stock and sometimes at the crossings if fab'd crossings.
Examples of S&C bonding from the IRSE document I linked to earlier. The coiled bonds shown in the first example are the 'pigtails' referred to.
bonding.jpg
 

MadMac

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I spent 40 years as an S&T Engineer but have been out of it a few years now. I haven't a clue either :lol: Must be some new fangled thing, or.......?
42 years and counting here, and it’s not a term I’ve ever heard. Suspect it’s some sort of bond.
 

themiller

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42 years and counting here, and it’s not a term I’ve ever heard. Suspect it’s some sort of bond.
Could it be a symptom of autocorrect putting flexity when Vindall 42 actually typed flexible? In typing this, I was corrected to flexitime!
 

Annetts key

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Steel galvanised bond wires are still required across joints until (if) the rails are welded together.
And between different switch and crossing components as described by MarkyT in post #8.

At rail expansion joints (to allow for rail expansion and contraction), although steel galvanised bond wires are sometimes used, normally 2.5mm² flexible rubber single core cable is used.

And with conventional track circuits (not audio frequency jointless types), the same cable is used for parallel bonding (to prevent any dead sections in the event of a broken rail or broken bonds) and for the feed end cables and the relay end cables.
 

seagull

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To turn the initial question around, how are track circuits separated in Continuous Welded Rail areas? Does the rail have to be cut and an insulating piece put in?
 

alxndr

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To turn the initial question around, how are track circuits separated in Continuous Welded Rail areas? Does the rail have to be cut and an insulating piece put in?
No, they use audio frequency track circuits instead, most commonly now EBItrack200 (formerly known as TI21). In these the rail is continuous and voltages of different frequencies are used to divide it into sections. The separation is done entirely electronically.

Is it something to do with the old ASTER Track circuits?

20 years on Track Renewals and never heard of Flexity strips either.
Not something I've come across with Asters either. I'm also of the opinion it's probably a typo/autocorrect error.
 

Annetts key

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To turn the initial question around, how are track circuits separated in Continuous Welded Rail areas? Does the rail have to be cut and an insulating piece put in?
Depends on if conventional track circuits are used, in which case insulated rail joints (IRJ or IBJ) are used. Or instead as said above, audio frequency track circuits are used. These use filter units and different frequencies to separate the different track circuit sections. No need for a IRJ or a break in the rail. Hence the railway preference for this type of track circuit on long sections of CWR.
 

MarkyT

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Depends on if conventional track circuits are used, in which case insulated rail joints (IRJ or IBJ) are used. Or instead as said above, audio frequency track circuits are used. These use filter units and different frequencies to separate the different track circuit sections. No need for a IRJ or a break in the rail. Hence the railway preference for this type of track circuit on long sections of CWR.
Indeed, jointless track circuits have been available since the 1960s, when continuously welded rail really started to become popular worldwide. The Aster 'U type' (universal) and the earlier '1 watt' (self-explanatory!) were early types employed in UK. ISTR the Aster TC was a French product originally. By the 1980s when I started on BR, Aster had given way to the more sophisticated TI21 (EBItrack200) as the standard jointless TC product for new schemes. That had the advantage of being compatible with DC and AC electrification, subject to certain configuration constraints. Of course there were still plenty of Asters out there in existing installations for decades to follow. I suspect Asters have become rather thin on the ground out in the field by now though if any still survive.

An interesting paper about the tech here: https://dickthesignals.co.uk/onewebmedia/aster book.pdf
 

Annetts key

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Indeed, jointless track circuits have been available since the 1960s, when continuously welded rail really started to become popular worldwide. The Aster 'U type' (universal) and the earlier '1 watt' (self-explanatory!) were early types employed in UK. ISTR the Aster TC was a French product originally. By the 1980s when I started on BR, Aster had given way to the more sophisticated TI21 (EBItrack200) as the standard jointless TC product for new schemes. That had the advantage of being compatible with DC and AC electrification, subject to certain configuration constraints. Of course there were still plenty of Asters out there in existing installations for decades to follow. I suspect Asters have become rather thin on the ground out in the field by now though if any still survive.

An interesting paper about the tech here: https://dickthesignals.co.uk/onewebmedia/aster book.pdf
ML engineering (Plymouth) made the ASTER units under licence from the French company. But went on to develop their own version that was compatible. Hence some units had ASTER written on them, but later units did not mention that name...

ASTER ‘U’ type were in use on Western up until about five years ago. The main reason that they were phased out was due to the lack of spare tuning units and ACT track side units. Most were converted to TI21/EBI types, which is a more modern equivalent.
 

MarkyT

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ML engineering (Plymouth) made the ASTER units under licence from the French company. But went on to develop their own version that was compatible. Hence some units had ASTER written on them, but later units did not mention that name...

ASTER ‘U’ type were in use on Western up until about five years ago. The main reason that they were phased out was due to the lack of spare tuning units and ACT track side units. Most were converted to TI21/EBI types, which is a more modern equivalent.
Thanks. So it follows the TI21 has a direct lineage from the Aster products.
 

MarkyT

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The TI21 equipment had the same style of housings as the Aster gear. It was essentially an AC-immune version of the Aster.
Makes sense. The TI was simpler in application too, with only two trackside tuning units per TC boundary rather than requiring a third unit, known as the track transformer, between them for the Aster.
 

alxndr

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ASTER ‘U’ type were in use on Western up until about five years ago. The main reason that they were phased out was due to the lack of spare tuning units and ACT track side units. Most were converted to TI21/EBI types, which is a more modern equivalent.
There were still some in use on the western up until last year, and I’m almost certain that they’re still there now. The spares are indeed becoming hard to come by now though. Some have been turned into hybrids, with TI21 equipment one end and Aster U the other. The frequencies used as close enough that they work.
 

swt_passenger

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So are we any clearer on what a “flexity strip”, (as the OP described it), actually is, because if not aren’t a few replies going off into unnecessary detail? Noting that the first two replies weren’t already aware of the terminology?
 

Annetts key

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There were still some in use on the western up until last year, and I’m almost certain that they’re still there now. The spares are indeed becoming hard to come by now though. Some have been turned into hybrids, with TI21 equipment one end and Aster U the other. The frequencies used as close enough that they work.
Do you have any idea where?

So are we any clearer on what a “flexity strip”, (as the OP described it), actually is, because if not aren’t a few replies going off into unnecessary detail? Noting that the first two replies weren’t already aware of the terminology?
No. I don’t know what he means.

If you go back to the past, to earlier than 1987, there were alternates to Steel galvanised bond wires. But I don’t think they were called “flexity strip”.
 

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