Hind Cylinder Cover

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A steam locomotive produces steam in its boiler which is fed through a regulator to the 2 cylinders fitted at the front of the locomotive. In the cylinders, the energy in the steam is converted to reciprocating motion. The connecting rod, connected to the piston in the cylinder converts reciprocating motion into rotary motion at the driving wheels.

The main, motion cylinder is the larger of the 2 cylinders in the cylinder block and contains a 2 way acting piston. At the appropriate time, steam is applied to one side of the piston to create movement. When the piston reaches the end of its stroke, steam is applied to the other side of the piston to reverse the stroke.

The valve cylinder sits above the main cylinder and its role is to control the entry of live steam and the exhausting of spent steam. The valve cylinder also acts like the gears of a car in that as the locomotive accelerates, steam is only applied for part of the stroke using the expansive properties of steam. This aids fuel economy.

The front of the main cylinder is closed by the front cylinder cover. This is essentially a circular disc closing off the front of the cylinder. A pressure relief valve is fitted to the cover.

The rear or hind cylinder cover is more complex as it has to provide for the exit of the piston rod. A gland seal (made of metal packing pieces) allows the piston rod to move while retaining steam pressure within the cylinder - which can reach a maximum of 250psi. The hind cylinder cover is also fitted with a pressure relief valve.

The rear of the piston rod is attached to a crosshead which, in turn, supports the little end of the connecting rod. The crosshead is supported by the slidebars. The purpose of the slidebars is to support the end of the piston rod thus ensuring that the piston is always perpendicular to the walls of the cylinder.

The piston is sealed in the cylinder by 2 piston rings fitted in circumferential grooves of the piston. From research we know that these locomotives suffered from abnormal wear of the piston rings. We believe that one cause was poor lubrication - which we will deal with separately. The other cause was likely to be movement of the slidebars.

We know that Bill Harvey, the shedmaster at Norwich in the 1950s (see Bill Harvey's 60 Years in Steam - Chaper 13) had been able to record movement of the front of the slidebars. If the slidebars were moving, then the piston rod would not be rigidly supported, inevitably leading to some undesirable wear of the piston rings.

We also know that British Railways had problems with loosening of the fasteners that secured the ends of the slidebars. This led to a fatal accident at Settle in 1960. It can be surmised that movement of the slidebars led to loosening of the fasteners.

British Railways made a modification to a small subset of locomotives whereby an extension to the hind cylinder cover casting provided a support to the front of the slidebars. This modification has recently been applied to an engine in preservation, namely 71000 Duke of Gloucester.

In June 2024, SSLC's team visited 71000 at Tyseley in Birmingham and the photo above was taken then. The hind cylinder cover has been modified to include an extension. The front fasteners of the slidebars are extended to also bolt the slidebars to the extension. We were able to obtain the original British Railways drawing for the modification and discuss the change with 71000's overhaul team. We were unable to use exactly the same design as 71000 as its cylinders are a smaller diameter. 71000 is a more powerful locomotive but has 3 cylinders as opposed to the 2 cylinders in our locomotive.

Since then our design team has been working to produce the Computer Aided Design model and drawings for the modification.

A formal Request for Quotation has been drawn up and issued to potential suppliers. After reviewing quotations, an order has been placed with Sutton Castings in Nottinghamshire. Casting is pencilled in for February 2025.