The first couple of weeks of 2023 has already seen some progress for two of the Fylde Transport Trust’s trams. The two in question are Twin Motor Car 281 and Coronation 304 with the former’s repaint almost completed in St Helens whilst for the popular Coronation Car there has been a significant delivery ahead of its eventual return to service.
We’ll start in St Helens where Twin Motor Car 281 is now residing having been moved from Rigby Road Depot on 18th April 2021. We featured the tram at the North West Museum of Road Transport last November where we saw that work was underway on its repaint to the original cream livery. Since then more work has been undertaken and now, save for a few finishing touches, the paintwork is complete and the tram now has its original number of 281 applied once more.
It is intended that 281 will remain on display at St Helens in this condition with it showing the period of its life when it had been converted to a Twin Motor Car but was not permanently coupled to a trailer. Its former trailer partner, latterly 681, remains in Blackpool and is owned by Blackpool Transport.
Meanwhile, the second week of January saw a significant delivery for the overhaul of Coronation 304. The seats were delivered back having been fully refurbished complete with new moquette. Once the interior of the tram has been completed this will allow them to be refitted inside the saloons again.
Elsewhere for 304, the new electrical equipment for the emergency braking system has arrived at the electrical contractors. Work on the modification on the tram will take place over the next month as well which will then allow testing and certification to take place. It remains the plan that the tram will be able to return to service during Coronation year although there does still remain some work to be done before this plan can be turned into reality.
Can anyone tell us what the modifications to the braking system entail exactly? I was told many years ago that fully electric VAMBAC cars such as ‘Pussyfoot’ at Crich had a design problem where it was possible for a contactor in the control gear to jam in the up position so the arm that swipes around the contactors to make the circuit could not physically go back into the braking notches. I understand Crich solved it by adding a button in the cab that when pressed would override the ‘knitting machine’ controller and dump full power into the track brakes when an emergency stop was required. However, if memory serves me correct, the Coronations have traditional air brakes as well as the VAMBAC electrical system and the normal handbrake.
As a passenger I’ve always liked the Coronations, but technically and financially they were definitely a very bad idea indeed! Hats off to anyone trying to get one back into service.
The PCC and early versions of VAMBAC c1946 (the PCC copy that was fitted to Blackpool208 and Glasgow 1005) used batteries to supply power to all the control systems It ensured that the electric brake was ALWAYS available, even if traction power was lost. As part of the changes to VAMBAC to overcome copyright issues (the UK was not allowed to purchase the licence due to wartime finance constraints post war). The system was re-designed so the accelerator would no longer stay in the correct position when coasting for the re-application of acceleration or brake. This was implemented by a clutch and return spring mechanism to reset the acclerator when the driver de-selected power or brake. With PCC the car never coasts, when the control is at off there is a small brake current flowing to keep the accelerator at the correct position.
At the same time some of the contactors were replaced with line voltage versions and the pilot motor for the accelerator also required line voltage to operate. This measn that is the trolley comes off the wire no electric brake can be activated (although the brakeing effect is still coming from the motors when it works).
To overcome this shortcoming the last brake position on the controller is an emergency brake which connects the motors directly to the track brakes using the battery supply to operate these contactors. BUT Blackpool removed the batteries to reduce weight so it only worked via a resistor from the traction supply!!! (these have been re-instated on 304)
The other problem (Coronation trams at Blackpool) was the weight combined with a poor air-brake which made stopping the tram very difficult during a Vambac failure or loss of traction supply. It is a requirement that trams have a secondary brake system and as the air brake is so poor the Coronation trams can not be stopped in the event of a Vambac failure or by the conductors emergency valve in the event of a driver colapse. This problem also applies to the Z-cars, in fact its worse as the conducuctors air valve can now not cut off the traction supply in the event of a driver colapse whist under power. There is no dead-mans controls on most first gen trams.
Now 602 aka pussyfoot. This was an all electric car (no airbrakes) and had electrically released shaft brakes (on the motor shaft-drive) and low voltage battery supplied track brakes (hence the size of the track brakes – 4 foot long!). As it still had some basic weaknesses in the Vambac braking system Crich modified it by adding over-ride switches in the cabs and platforms which cut traction power (opened the line-switch) and applied the track and shaft brakes independently of any traction supply or any other part of the Vambac system, a manual over-ride.
Just to add the use of the Guard’s emergency valve uses a primitive way of cutting power – the brake action on the wheels causes the breakers to blow (or should) and cuts power. In the case of the Coronations they were still too heavy to stop with the air application!
There was only one all-elecric Vambac car and that was/is Leeds 602.
Whether this design fault was common to Glasgow 1005, Blackpool 10-21, 208, 303 and their Vambac equipment is something I don’ recall reading about, except in a very generalised way. In fact I don’t recall seeing anything reliable about Vambac equipment’s faults in service, though we all know there were plenty.
Were they simply teething troubles, were there more fundamental design flaws in Vambac equipment or was it just a case of a steep learning curve that was never wholly surmounted? Tens of thousands of sets of all-electric PCC equipment were made from 1940 until at least the 1970s and the troubles they had initially were soon ironed out.
As I understand it, VAMBAC differed from PCC control systems in one major way. The thing often in the trolley towers of a VAMBAC that is often called the ‘knitting machine’ was a circular arrangement of contactors, which a main contact wiper would work it’s way around, making the corcuit with one of the array of contactors in turn. It went one way for the power notches and the opposite way to ‘throw off’ and then go into the braking notches. The PCC design had a statin set of contactors and a wiper arm that moved down slightly to meet each one in turn and make the circuit. However to get around patents the VAMBAC system employed multiple contactors that moved up to meet the wiper rather than the wiper being pulled down. The problem arose when a contactor that had been passed got stuck and remained in the up position. This meant that when the driver threw off the power the wiper could not retirn to rest or into the braking notches because the stuck contactor blocked it’s path. The result was not being able to brake and sometimes not even being able to cut power using the normal driving controls. I believe Blackpool got around the problem to some degree by using the air brakes as the service brake, rather than the VAMBAC which was intended to be used as a service brake. That’s why I’m a bit surprised that a Coronation requires modification as it’s got both an air brake and a hand brake. However I’m not sure how good either of these would be if the VAMBAC system was stuck in a power notch. At least that’s the story I was told by a now long dead electrical engineer.
In reply to your question, the modification being undertaken on 304 is to add a completely independent emergency brake system that can be activated from either cab and also from a saloon mounted emergency stop. The new system will safely bring the tram to a stop bypassing the VAMBAC controls. This sounds a simple modification, but is actually quite a complex modification that has been designed by a specialist company and approved by BTS (as the operating authority).
Andy you cannot stop a Coronation on the air – 304 went into the back of a bus at Beamish at slow speed when a novice deiver tried to. The Z4 converts were always braked with the rheostatic brake. The air is holding only. Likewise the handbrake is parking only. The VAMBAC railcoaches could be stopped with the air as they are lighter. But neither would be effective if it was still drawing power and you would cause the breakers to blow. It would also take too long to stop and therefore be dangerous.