Deleted
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Post by Deleted on Jul 30, 2005 21:49:25 GMT
I understand the basic principle of a tripcock, but does anyone have any information on how the tripcock actually works?
I'm mainly curious as to how the tripcock is linked to the main line air, and how the valve that exhausts that system is actuated by the lever.
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Tom
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Post by Tom on Jul 30, 2005 22:25:04 GMT
I understand the basic principle of a tripcock, but does anyone have any information on how the tripcock actually works? I'm mainly curious as to how the tripcock is linked to the main line air, and how the valve that exhausts that system is actuated by the lever. Haven't got a clue about how it exactly works, but I know that it's train line air that gets vented.
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solidbond
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Post by solidbond on Jul 30, 2005 22:31:58 GMT
I understand the basic principle of a tripcock, but does anyone have any information on how the tripcock actually works? I'm mainly curious as to how the tripcock is linked to the main line air, and how the valve that exhausts that system is actuated by the lever. Haven't got a clue about how it exactly works, but I know that it's train line air that gets vented. Depends on the stock On stock that HAVE train line air, then indeed it is train line that is vented when the tripcock is operated. However, with the introduction of the 73 stock, and all stock since then, it is main line air that is vented, which causes pressure switches to drop, breaking the electrical circuits of the braking circuit ;D
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Deleted
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Post by Deleted on Jul 30, 2005 22:34:32 GMT
Hm, I thought it was called main line air.
Tubeprune implies that the 1973TS was the first to make the switch to a single air circuit, but I could be reading it wrong.
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Tom
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Post by Tom on Jul 30, 2005 22:39:43 GMT
Tubeprune is correct, in stock prior to 1973 it was train line air that gets discharged, post 73 main line air is the only supply used so has to be vented.
Though I thought the tripcock on 73TS directly operated on the 50v round the train circuit which in turn opened the air to atmosphere?
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solidbond
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Post by solidbond on Jul 30, 2005 23:16:06 GMT
Tubeprune is correct, in stock prior to 1973 it was train line air that gets discharged, post 73 main line air is the only supply used so has to be vented. Though I thought the tripcock on 73TS directly operated on the 50v round the train circuit which in turn opened the air to atmosphere? 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 piccadillypilot on Jul 30, 2005 23:25:34 GMT
I can confirm that Solidbond is correct.
When the trip arm is activated it opens a valve which releases a small amount of air that has been supplied by the Mainline.
That air escaping allows two pressure switches to open breaking the Full Speed and 10mph Safety Brake Circuits. Via a sequence of relays this in turn opens the brake application valves which admits Mainline air to the brake cylinders.
If the train loses Mainline air for any reason then the Spring Applied Parking Brakes will apply.
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Post by piccadillypilot on Jul 30, 2005 23:34:24 GMT
Haven't got a clue about how it exactly works, but I know that it's train line air that gets vented. On those trains so fitted the trip arm being activated simply open a stonking big hole in the valve which allows Train Line Air to escape to atmosphere. This causes the Control Govenor to open, breaking the motor control circuit and disconnecting the traction from the motors. The escape of Train Line air cause the Primary Piston in the Triple Valve to move over hard against the Buffer Spring allowing ports in the Slive Valve to open and air from the Auxiliary Reservoir to enter the Brake Cylinder. The force of the Primary Piston moving causes additional ports to open in the Slide Valve causing an additional 5lb of air from the Triple Valve bulb to enter the Brake Cylinder. Curently this only applies to A60/6s stock as later trains are fitted with distributor valves instead of Triple Valves, however the principle remains the same.
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towerman
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Post by towerman on Jul 31, 2005 0:08:35 GMT
Thats the correct theory,had a train come out of service at Hainault once,tripped past 3 sticks during a signal failure and nothing happened.Tested it myself with a shoe paddle,sure enough there was a little puff of air but no emergency application.On closer inspection the chamber on top of the tripcock was hanging off and the mechanism to vent train line air was jammed. The guy who signed the trip sheet the previous night was dipped to a cleaner for a year.
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Post by piccadillypilot on Jul 31, 2005 8:15:21 GMT
As always on the railway, if people don't do their job properly other people are put in danger. Someone must have been on his side. People have been sacked for less.
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Deleted
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Post by Deleted on Jul 31, 2005 22:47:57 GMT
If you are behind the cab, you can hear the noise of the pressure switches dropping out, nothing spectacular, but noit a noise you want to hear! The Spring Applied Parking Brake comes on if Main Line air drops below 4 bars, the Train Operator cannot release it until air is restored. SAPBs are not fitted to trailer cars, they are only on motor cars, one per axle, and as stated the train operator has no direct control over hem.
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towerman
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Post by towerman on Aug 3, 2005 3:49:55 GMT
Actually,It cost the guy a lot of money,as well as going down to cleaner's wages,he was one of the senior car examiners so he lost a lot of higher duty pay and overtime.
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