Parry People Movers

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Parry People Movers
Bristol Electric Railbus.jpg
PPM No. 35 at the Ecclesbourne Valley Railway, Wirksworth.
Track gauge 1,435 mm (4 ft 8 12 in) standard gauge

Parry People Movers Ltd. (PPM) is a British company manufacturing lightweight trams and railcars that use flywheel energy storage (FES) to store energy for traction, allowing electric systems to operate without overhead wires or third rails, and railcars fuelled by small gas, diesel or hydrogen engines.

Current usage[edit]

London Midland, owner of the West Midlands franchise, began operating a single PPM50 (Class 999) unit on the Stourbridge line on Sundays in 2006, with a Class 153 diesel multiple unit (DMU) providing a weekday service. In June 2009, the Class 153 was replaced by two PPM60 units, classified as Class 139 (with one as spare), providing a 10-minute frequency in both directions. Although the capacity of the unit (60 passengers) is less than the DMU, overall capacity is increased due to the greater frequency, up from 4 to 6 trains per hour.

From 24 January 2011, Go! Cooperative planned to be operating a trial service between Alton and Medstead & Four Marks on the Mid-Hants Railway using the Class 999 unit.[1] This was abandoned after a series of mechanical and electrical failures and due to the unit proving to be unsuitable for the long and steep gradients on the line[2] the unit is now being reconfigured to address the problems with a redesigned chassis and conversion from LPG to Diesel power and the trial will be repeated.[3][4]

In January 2012, plans emerged for new bigger PPMs to be used on the South Staffordshire Line between Stourbridge Junction and Brierley Hill, providing passenger services on the line for the first time since the Beeching Axe.[5]

Earlier trials[edit]

Trial on Stourbridge Town Branch Line

The Parry flywheel storage technology was tested on the Stourbridge Town Branch Line in the West Midlands in 2006. Since Central Trains had no Sunday service on the branch, the initiative was brought to test a PPM50 model at that time, with a view to replacing the Class 153 single-car Diesel Multiple Unit that previously worked the Branch with a unit with much lower operating costs. The trial lasted for a year.

Parry People Movers have also been demonstrated on narrow gauge railways (Welshpool and Llanfair Light Railway, Ffestiniog Railway, Welsh Highland Railway).[6]


PPMs utilise a rotating flywheel as a store of kinetic energy which is then used to power the vehicle. A typical PPM flywheel is made from steel laminates, approximately 1 m (39 in) in diameter and 500 kg (1,100 lb) in mass, designed to rotate at a maximum speed of 2,500 rpm.[7] The flywheel is mounted horizontally at the centre of the unit, beneath the seating area. The flywheel is driven by an internal combustion engine or an electric motor. The flywheel is connected to the rail wheels via a hydrostatic variable transmission system.

The flywheel allows the direct capture of brake energy (when slowing down or descending gradients) and its re-use for acceleration (called regenerative braking). When the vehicle brakes, the hydrostatic transmission feeds the energy back into the flywheel. Since the short-term power demand for acceleration is provided by the energy stored in the flywheel, there is no need for a large engine. A variety of small engine types can be used including LPG, diesel or electric traction.

On a route with stations a short distance apart it is theoretically possible to use the unit as a tram without any engine or overhead electrification at all. Instead the flywheel could be re-energised at each station storing enough power to carry it on to the next.


Class Operator No. Built Year Built Cars per Set Unit nos. Carriage nos. Length Seated Standing
Class 139 Pre-Metro Operations on behalf of West Midlands Railway 2 2008 1 139001 - 139002 39001 - 39002 9.6 m 25 35
Class 999 Pre-Metro Operations 1 2002 1 999900 999900 8.7 m 20 30


  1. ^ (retrieved 18 January 2011)
  2. ^ (retrieved 19 January 2011) Archived 17 May 2011 at the Wayback Machine.
  3. ^
  4. ^ "Archived copy" (PDF). Archived from the original (PDF) on 26 April 2012. Retrieved 12 April 2012. 
  5. ^
  6. ^ Welsh Highland Railway Society web site
  7. ^ "PPM Technology". Parry People Movers. Retrieved 2008-10-13. The rotating flywheel is a store of kinetic energy that is used to power the vehicle. A typical PPM flywheel is made from steel laminates, 1 m (39 in) in diameter and 500 kg (1,100 lb) mass, rotating at a maximum speed of 2,500rpm 

External links[edit]