MPV Rear Tripping (Back Tripping)

[Gunjani]

I don't know much about MPVs, but does anyone know anything about MPVs rear or back-tripping, generally and specifically on the MerseyRail. I heard it is a frequent nuance on the Merseyrail, which I find odd. I would like to know if it is a common occurrence on all North West Network Rail Infrastructure or just specific to MerseyRail?
It would be great to receive some useful feedback on root causes: tripcock gauging, speed, train length etc.

 

[Bletchleyite]

Tripcocks aren't used outside of Merseyrail and London Underground, so they wouldn't be triggering anywhere other than those places?

 

[Gunjani]

Which also raises the question why are Tripcocks used on MerseyRail, as they are oddly not located every signal, they are only primarily at crossovers. Why not just stick to one protection system, would it not be cost effective?

 

[Bletchleyite]

Which also raises the question why are Tripcocks used on MerseyRail, as they are oddly not located every signal, they are only primarily at crossovers. Why not just stick to one protection system, would it not be cost effective?

They are at high risk locations - crossovers (didn't know that) and all signals (I think) in the tunnel sections. They predate TPWS (they have been installed from the start of the underground operation). It is certainly conceivable that they could be replaced by TPWS which does the same thing a different way, but if it ain't broke...

Were they installed on underground railways (Tube) as a result of the Moorgate accident or similar? I can't remember to be honest.

TPWS is now used on other parts of the network where tripcocks were not installed, if I recall rightly.

 

[pdeaves]

Were they installed on underground railways (Tube) as a result of the Moorgate accident or similar?

Trip cocks were around way before Moorgate. Some other control was introduced after that accident but I can't remember what.

 

[Taunton]

Tripcocks have I understand been installed on both the London Tube and Merseyrail since earliest times. They originally came from the USA, whose signalling contractors brought them over to both systems.

Moorgate would not have been prevented by conventional tripcocks, as there was no signal passed at danger. The advent of "Moorgate controls" was putting additional signals spaced a short distance apart, with timing relays between them clearing so one can't exceed a certain speed on the final approach to the end of the line. However, as a serious accident on the Toronto system showed, where these are called "Grade Timing Signals", even that similar concept was not immune.

 

[The exile]

Tripcocks have I understand been installed on both the London Tube and Merseyrail since earliest times. They originally came from the USA, whose signalling contractors brought them over to both systems.

Moorgate would not have been prevented by conventional tripcocks, as there was no signal passed at danger. The advent of "Moorgate controls" was putting additional signals spaced a short distance apart, with timing relays between them clearing so one can't exceed a certain speed on the final approach to the end of the line. However, as a serious accident on the Toronto system showed, where these are called "Grade Timing Signals", even that similar concept was not immune.

The Tooting Broadway accident of ?1970 led to LT changing the default aspect of a signal on the approach to a dead end from “all clear” to “caution”. The programme was still ongoing in 1975 and possibly because of the impending transfer to BR this had not been implemented at Moorgate.

 

[Lucy1501]

Which also raises the question why are Tripcocks used on MerseyRail, as they are oddly not located every signal, they are only primarily at crossovers. Why not just stick to one protection system, would it not be cost effective?

They were seemingly a favourite of the Mersey Railway, and the line to James Street was fitted before the loop and link schemes. When the loop line was constructed they continued with the same and only practical method of train protection.

As part of the construction of the link and loop, the Northern Line stock was fitted with trainstops to allow interoperability, and the Mersey stock modified to work with the BRB standard design.

All signals in the link and loop, and on the approach, were fitted with tripcocks. The number proposed was 50 - how that stacked up in the end I don’t know.

I suppose the rationale behind keeping the tripcocks in the scheme was the relatively unique metro style signalling system and the whole risk from tunnels. Certainly in the loop most of the signals do not have a yellow aspect. The sighting distance is the braking distance, and the tripcock has to guarantee the train stops in the overlap.

Trip cocks were around way before Moorgate. Some other control was introduced after that accident but I can't remember what.

Two sidings were fitted with “Tooting” controls halfway down the sidings at James Street and Liverpool Central. These were set to lower on a timer after track circuit occupation, which was based off of the maximum permissible speed.

It would be great to receive some useful feedback on root causes: tripcock gauging, speed, train length etc.

More generally there was a document released under a FOI request for the loop & link working instructions which has details on trip cocks, found here: https://files.whatdotheyknow.com/re...str/NR_L3_ELP_27051_MANUAL (003)_redacted.pdf

 

[Gunjani]

Thanks for the pdf. I may come back to you once I have digested it.

They were seemingly a favourite of the Mersey Railway, and the line to James Street was fitted before the loop and link schemes. When the loop line was constructed they continued with the same and only practical method of train protection.

As part of the construction of the link and loop, the Northern Line stock was fitted with trainstops to allow interoperability, and the Mersey stock modified to work with the BRB standard design.

All signals in the link and loop, and on the approach, were fitted with tripcocks. The number proposed was 50 - how that stacked up in the end I don’t know.

I suppose the rationale behind keeping the tripcocks in the scheme was the relatively unique metro style signalling system and the whole risk from tunnels. Certainly in the loop most of the signals do not have a yellow aspect. The sighting distance is the braking distance, and the tripcock has to guarantee the train stops in the overlap.




Two sidings were fitted with “Tooting” controls halfway down the sidings at James Street and Liverpool Central. These were set to lower on a timer after track circuit occupation, which was based off of the maximum permissible speed.



More generally there was a document released under a FOI request for the loop & link working instructions which has details on trip cocks, found here: https://files.whatdotheyknow.com/request/merseyrail_drayton_park_dc_instr/NR_L3_ELP_27051_MANUAL (003)_redacted.pdf

Thanks for the detail response and the pdf. I may come back to you. I am attempting to
find a solution to the rear trips on MerseyRail for the MPVs.

== Doublepost prevention - post automatically merged: 19 Mar 2026 ==

They were seemingly a favourite of the Mersey Railway, and the line to James Street was fitted before the loop and link schemes. When the loop line was constructed they continued with the same and only practical method of train protection.

As part of the construction of the link and loop, the Northern Line stock was fitted with trainstops to allow interoperability, and the Mersey stock modified to work with the BRB standard design.

All signals in the link and loop, and on the approach, were fitted with tripcocks. The number proposed was 50 - how that stacked up in the end I don’t know.

I suppose the rationale behind keeping the tripcocks in the scheme was the relatively unique metro style signalling system and the whole risk from tunnels. Certainly in the loop most of the signals do not have a yellow aspect. The sighting distance is the braking distance, and the tripcock has to guarantee the train stops in the overlap.

What stations or are fall under the link? I assume the link is the Northern line part of the underground?

 

[Lucy1501]

What stations or are fall under the link? I assume the link is the Northern line part of the underground?

The link is the Northern Line’s underground section, so named because it linked Liverpool Central Low Level with the line to Liverpool Exchange which was closed as part of the project.

 

[john prytherch]

What does "MPV" stand for please?

 

[Bletchleyite]

What does "MPV" stand for please?

Multi Purpose Vehicle I believe. They're purpose built Network Rail "2 car DMUs" used for various forms of maintenance; they replaced the old converted EMUs.

 

[Taunton]

They were seemingly a favourite of the Mersey Railway, and the line to James Street was fitted before the loop and link schemes.

I suppose the rationale behind keeping the tripcocks in the scheme was the relatively unique metro style signalling system and the whole risk from tunnels.

They were installed by Westinghouse in the 1923 resignalling of the Mersey Railway, which used components from the USA including train stops and automated operation. When through running from the LMS began in 1938 their new trains, which later became Class 503 and now formed alternate trains through the tunnel, were likewise fitted, and this signalling carried on until the loop was built in 1977, when it was replaced. This article on the 1923 resignalling refers to the train stops:

Westinghouse Brake & Saxby Signal Co. Ltd. Hamilton Square signal box

The 1938 LMS trains were built by Met-Cam and Birmingham RCW at the same time as the Underground sub-surface O and P stocks, and many aspects of the design carried from one to the other, so the designers and builders would have been very familiar with incorporating train stops in the vehicles.

 

[matchmaker]

The Glasgow Subway did have tripcocks, but they are no longer needed with the new rolling stock. The previous Metro-Cammell stock was fitted with them.

 

[Belperpete]

Didn't some of the LMS DC lines in the London area also use trip cocks? Such as the NLL. And the Liverpool Overhead?

The Waterloo and City also used trip cocks long before it came under LT control. I remember being told by the ASE at Clapham Jcn that the trip cocks for the W&C, Wimbledon and Richmond branches were all sent to LT when they needed refurbishment, but they had to make sure they didn't get mixed up as the W&C ones were not LT-standard size.

 

[philthetube]

Technically the tripcock is the bit on the train and the trainstop is the bit on the ground.

I struggle to see why rear tripping should be an issue, perhaps someone knows more?

The protection provided by train stops at termini on London underground is normally one or 2 located a distance from the end of the line which will lower at ten mph in order to ensure a slow arrival into the station. This is not needed when lines are converted to ATO

A less technical solution than is used on the main line but equally effective

 

[MrJeeves]

Some other control was introduced after that accident but I can't remember what.

The helpfully named "Moorgate protection". Or its proper name, TETS (Trains Entering Terminal Stations) which applies the emergency brakes if the train travels over 12.5 mph into a terminal platform.

It was actually already being installed before the crash at Moorgate, but they hadn't gotten round to installing it at Moorgate by the time of the incident.

 

[AndrewE]

post #13 has an interesting date, I thought the Liverpool Overhead might have been the pioneer. Wikipedia says

The first automatic train-stop system was installed on the line and was electrically operated. An arm on the trackside would be struck by each passing train, activating an electromagnet, resulting in a 'danger' signal being shown until the train had passed through the next station. As a result of automation, the number of staffed signal boxes was reduced to two. The line upgraded the signalling from semaphore to a Westinghouse permanent daytime colour-light system in 1921: the first to be installed in Britain.[32] The track also contained automatic braking systems for trains which ran through a red light; the current could be automatically disconnected and air brakes applied

but doesn't give a precise date for the train-stops, but presumably the same as the 1921 signals.

I suspect that if a 2-vehicle train has train-stop trips at each end and the signal reverts to danger pdq as the cab passes it then the rear cab trip-cock night well be triggered by the red signal...

 

[Friary Yard]

As I understand it "Moorgate Protection" consisted of train stops located at intervals along the platform line and lowered in a timed sequence to allow a train travelling at permitted speed to pass but that a train travelling at excess speed would be tripped before the train stop had lowered

 

[Stuart-h]

I might be able to help as I sign mpv’s round Mersey side.

 

[philthetube]

As I understand it "Moorgate Protection" consisted of train stops located at intervals along the platform line and lowered in a timed sequence to allow a train travelling at permitted speed to pass but that a train travelling at excess speed would be tripped before the train stop had lowered

yes.

As I understand it train speed was measured by track circuits

 

[Belperpete]

I suspect that if a 2-vehicle train has train-stop trips at each end and the signal reverts to danger pdq as the cab passes it then the rear cab trip-cock night well be triggered by the red signal...

Surely the rear-end trip-cocks should be disabled?

Having said that, I recall the designer responsible for the W&C installation saying that it was more complicated than an LT installation, by the need to lower the "Moorgate" trip-stops for departing trains, due to the W&C trains' trip-cocks being active at both ends of the train.

 

[Dstock7080]

Surely the rear-end trip-cocks should be disabled?

Having said that, I recall the designer responsible for the W&C installation saying that it was more complicated than an LT installation, by the need to lower the "Moorgate" trip-stops for departing trains, due to the W&C trains' trip-cocks being active at both ends of the train.

LT/LU tripcocks remain active at both ends, middle cabs are isolated by the process of coupling.
LT terminal protection trainstops remain lowered until the train departs.

 

[jamesst]

The track trip equipment is on the right hand side of the track (as is the trip cock under the train) so rear tripping is only generally a thing is theres some kind of item on the right hand side on the track at the other end.

In the case of bidirectional lines the train stop of the opposing signal will be lowered before the signal can be cleared in the correct direction. On Merseyrail this can be heard for example if you stand at the Liverpool end of the up platform at Hamilton Square Station and a train is being signalled into the opposite platform.

As for the 777s (&the 50xs before them) if running in 8car formation the 2 trip cocks in the middle cabs automatically raise as part of the coupling process.

 

[norbitonflyer]

The track trip equipment is on the right hand side of the track (as is the trip cock under the train) so rear tripping is only generally a thing is theres some kind of item on the right hand side on the track at the other end.

In the case of bidirectional lines the train stop of the opposing signal will be lowered before the signal can be cleared in the correct direction.

This provision is presmuably only considered necessary on a bidirectional line, so rear tripping could occur, if for any reason, a train was required to run "wrong line". I guess MPVs, by the nature of the work they do, are more likely to be required to do this. (eg in an engineering possession)