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Post by Deleted on Sept 21, 2005 15:30:02 GMT
There's a thread doing the rounds in u.t.l. right now about all the issues being experienced by the Northern Line; somebody named bowroaduk@yahoo.com posted the following: "The normal testers only check that the tripcock is 1) in place, 2) in gauge - the present problem was caused when a train was tripped travelling at slow speed (not "in slow speed") and the tripcock effectively reset itself, thus failed to operate the Tripcock Pressure Switch which applies the brakes." La poste de reference. Is anyone able to expound on this issue, and explain as to how a tripcock could reset itself? |
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Phil
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RIP 23-Oct-2018
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Post by Phil on Sept 21, 2005 15:53:07 GMT
Surely irrelevant: does not every train pass a tripcock tester as it leaves the depot each morning??
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Post by Deleted on Sept 21, 2005 16:16:24 GMT
As bowroaduk's post said, the tester only checks to see if the tripcock is present and properly gauged - it doesn't actually see if the tripcock actually works...
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Post by Deleted on Sept 21, 2005 17:57:10 GMT
Surely irrelevant: does not every train pass a tripcock tester as it leaves the depot each morning?? The problem didnt lie with the lack of tripcocks, it was an issue that the tripcock was resetting itself automatically. A tripcock tester purely tests to see it a tripcock is there rather than if it actually does what it should do. Contrary to BBC news, all of the affected sets of 95ts have been withdrawn from service pending the modification to stop this problem re occuring. Strangely the defect isnt affecting the whole of the fleet, thus meaning they can keep some sort of service on the road. The quote from the news group refers to the 'tripcock pressure switches'. I wouldnt say that is 100% right, as i was under the understanding that when the tripcock is operated, it allows air to escape, this makes the pressure switches drop out, which applies an emcy brake as the RTC is broken. Am I right ?! |
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Post by Deleted on Sept 21, 2005 19:01:12 GMT
Surely irrelevant: does not every train pass a tripcock tester as it leaves the depot each morning?? The problem didnt lie with the lack of tripcocks, it was an issue that the tripcock was resetting itself automatically. A tripcock tester purely tests to see it a tripcock is there rather than if it actually does what it should do. Contrary to BBC news, all of the affected sets of 95ts have been withdrawn from service pending the modification to stop this problem re occuring. Strangely the defect isnt affecting the whole of the fleet, thus meaning they can keep some sort of service on the road. That's odd. Are the affected tripcocks part of a certain build set or are they randomly distributed? The quote from the news group refers to the 'tripcock pressure switches'. I wouldnt say that is 100% right, as i was under the understanding that when the tripcock is operated, it allows air to escape, this makes the pressure switches drop out, which applies an emcy brake as the RTC is broken. Am I right ?! solidbond explained it thus: Not true  If the tripcock was to act directly on the 50v DC circuit, there would have to be some pretty robust contacts that could withstand the onslaught of the tripcock being hit at up to 50mph or more  What actually happens is that, as stated in my previous post, there are pressure switches kept in circuit by main line air. When the tripcock is operated, main line air is vented causing the pressure switches to drop, thus breaking the safety brake circuits, thus applying the brakes. I will say, however, that there is a choke in the main line supply to the tripcock to restrict the amount of main line air that is lost when the tripcock is operated, to prevent a complete loss of main line air. |
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Post by Deleted on Sept 21, 2005 23:03:55 GMT
If, everytime you tested the tripcock, you tripped the train, it would cause no end of delays. Which is what the u.t.l. thread said was going on - trains were being deliberately tripped at all of the termini to test their tripcocks; any train that did not behave appropriately after getting tripped was taken out of service. Apparently it quite thoroughly b*****ed the service... |
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Post by Deleted on Sept 21, 2005 23:11:25 GMT
Which is what the u.t.l. thread said was going on - trains were being deliberately tripped at all of the termini to test their tripcocks; any train that did not behave appropriately after getting tripped was taken out of service. Apparently it quite thoroughly b*****ed the service... Yep, that has been done to purely test the train, however as you say, if it was more permanent, it would knacker the service sideways!  |
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Post by robots on Sept 21, 2005 23:43:52 GMT
Just to clarify , after being tripped some units were automatically resetting so no time
delay was operating. It 's not entirely clear from the news reports or the thread what
exactly is causing this.
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Post by trainopd78 on Sept 22, 2005 8:40:12 GMT
The thing that's confusing me is that trains are physically tripped by the fitters when being prepared overnight in the depot's or sidings, so the defect could have only been a few hours old  |
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Post by Deleted on Sept 23, 2005 17:13:30 GMT
From what I've read on LU's Intranet, the problem was a fairly simple remedy.
Fixed train stops were inserted in 5 locations, and all trains on Saturday operated past these train stops under failure conditions.
Half the fleet were found to have a problem, which was fixed on Sunday.
On Monday, the tests remained, to test the problem had been fixed....
My understanding of the problem was more mechanical in nature.
But I've only read the reports and haven't heard first hand.
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Post by markextube on Oct 2, 2005 22:42:41 GMT
I see there was another report about this in the papers last week.
When i drove the 95's i had a few incidents where the trip would hit somthing then spring back. Sometimes it would activate the brakes but very briefly with a jolt then release.
To be honest with what i've experienced with this stock and with the camden derailments i'm suprised they were passed as fit.
Few examples
Brakes failing on more then one occasion
Trip playing up or not resetting
Door closing by themselves
Pilot light loss because of passengers in the train
deadman not doing what its supposed to and train runs backwards....etc
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If the tripcock was to act directly on the 50v DC circuit, there would have to be some pretty robust contacts that could withstand the onslaught of the tripcock being hit at up to 50mph or more 
What actually happens is that, as stated in my previous post, there are pressure switches kept in circuit by main line air. When the tripcock is operated, main line air is vented causing the pressure switches to drop, thus breaking the safety brake circuits, thus applying the brakes. I will say, however, that there is a choke in the main line supply to the tripcock to restrict the amount of main line air that is lost when the tripcock is operated, to prevent a complete loss of main line air. 
