Here is an internal R & D document about the experimental hydrostatic drive single car unit Hydra and a few pictures.

Single car unit No: RDB 975385 (formerly a Cravens parcels car No:M55997) was converted as a test bed for hydrostatic drive in 1980 and was known as 'Laboratory 9  Hydra'.

It was fitted hydrostatic transmission having the normal Leyland 680 six cylinder engine driving two Rexroth Hydromatic axial piston pumps. Each pump supplied fluid to a Volvo fixed displacement compact axle-end motor which drove the axle directly. The maximum system pressure was in the order of 400 bar.

This arrangement was only fitted to one bogie, the other one retaining its normal drive but with the cardan shaft disconnected.

It ran for few years as a development vehicle but the unit was finally scrapped by Vic Berry at Leicester.

What's it all about?

The article explained the background and operation of the hydrostatic drive system

Author's collection


Hydra on Etches Park depot


In the yard

A better version of the article's photo of Hydra in the RTC Yard

Author's collection

In the yard at RTC

Hydra sits in the sidings outside the Advanced Projects Lab in the early 1980's


Hydra at Mickleover

And here it is near Mickleover at the Mickleover test track 

Colin Marsden

Hydra at Etwall

At Etwall station on the Mickleover line in August 1984

Tony Woof

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