Sunday, 14 December 2008

Medway Queen - Rebuild of a Dunkirk Veteran Part 1

Part 1 - Machinery arrives in Bristol
(words by G Stewart, Photos by Dave Elms)

Back in September it was announced by the Medway Queen Preservation Society that a contract had been placed with David Abels (Boatbuilders) in Bristol to manufacture a new rivetted hull for the 1924 Clydebuilt paddler Medway Queen.

Machinery has now started to arrive at the Albion Dockyard in Bristol and thanks to good friend and Abels engineer Dave Elms the moment on Sat 6th December was captured on camera.

The following shots show the main engine cylinder block arriving and being offloaded. Medway Queen has a compound diagonal steam engine which was manufactured by her builders Ailsa.

In this shot of the Main Engine the Andrews Cameron low pressure (LP) slide valve can be seen. This valve facilitated the transfer of exhaust steam from the LP cylinder to the condenser and also admitted steam to the LP cylinder from the high pressure (HP) cylinder.


This valve would be driven via rods and linkages from the Main Engine Crankshaft.



Another view shows the engine control levers on top of the engine block. There are 5 levers in all - the throttle which regulates the admission of high pressure steam from the boiler to the HP cylinder, ahead /astern direction control lever, 2 x cylinder drain control levers which open the cylinder drains to allow any condensate which may have collected in the cylinders whilst the engine was stopped to be evacuated by the live steam entering the cylinder and finally the impulse valve lever. This lever permits the
entry of HP steam into the LP cylinder

which, due to the vastly greater surface area of the LP piston, gives the engine a "kick" of HP steam. This was used to start the engine if it stopped in a position which did not permit steam to be admitted to the HP cylinder or if a short burst of speed was suddenly required.

On the right of the photo the LP psiton rod can be seen which still has its crosshead complete with "slippers" attached. The crosshead permitted connection of the piston rod to the crankshaft connecting rod. The slippers would normally be making contact with slides which ensured that the piston rod remained supported and also was allowed to slide in and out of the engine block - the slippers are usually lubricated via grease or oil. The crosshead permitted connection of the piston rod to the crankshaft connecting rod. This connection pivots which allows the crankshaft connecting rod to rotate the crankshaft.



A shot of the Main Engine Crankshaft complete valve gear eccentrics attached. These operate the HP & LP valves which control the admission and exhaust of steam from each cylinder. In the case of the Medway Queen the rotating motion of these eccentrics was converted to a sliding motion via a rocking link. Another smaller crosshead connection is used to attach the valve rod which slides in and out of the engine block. This type of valve actuation is called Stephenson Valve Motion and was widely used in steam locomotives as well as reciprocating steam engines. Waverley's Rankin and Blackmore main engine also utilises Stephenson Valve Motion. Another method of actuating the valvegear on paddlesteamers was called Brock Valve Motion and was invented by the Chief Engine Designer at Denny Bros of Dumbarton. This type of valve motion was used for the engines of the famous Clyde paddler Caledonia and her sister Mercury.

In this final shot we can see what looks like a steam operated boiler feed pump in the foreground - perhaps built by the famous company Weirs of Cathcart. The red coloured equipment behind this could possibly be the air pump - which permits the transfer of condensate from the condenser back to the hotwell to be pre-heated prior to transfer back to the boiler via the forementioned boiler feed pump - but I am open to suggestions via the comments facility below!!



I am hopeful that Dave will continue to provide us with fascinating photos such as these as it is not every day a new paddler hull is commissioned!


Thanks Dave!


Gavin Stewart

2 comments:

valve replacement said...

Complex control systems using valves requires an automatic control based input of an actuator. The actuator strokes the valve allowing the valve to be positioned accurately and allowing control over a variety of requirements.

james mitchell said...

yes, engine driven air pump unlike Waverley or the Maid, which are self powered.
two simplex weir feed pumps... We need two for the Maid, if anyone falls over one (or two) on their wanderings!