Parkandillick Gallery 3: This page has images of the Middle Chamber which houses the top of the 50″ cylinder, the valve chest and the piston rod rising to the beam above.
Parkandillick Gallery 3.1 – The first view of the Middle Chamber. The balustrading, so commonly found in engine houses. The timber work was really something to be proud of, it did not matter if it was a clay engine or a mining engine.Parkandillick Gallery 3.2 – The top of the 50″ cylinder along with the piston rod. In the wooden beam at the top of the image is graffiti dated 1935.Parkandillick Gallery 3.3 – Apart from the heaters on the wall this room has changed little since the engine was retired.Parkandillick Gallery 3.4 – When the engine was in work the building would have been spotlessly clean along with potted flowers on the window cills. The big round beam at the top of the frame is the anchor point for the parallel motion radius rods. This is also braced to the bob wall.Parkandillick Gallery 3.5 – The top of the cylinder and the piston rising to the floor above.Parkandillick Gallery 3.6 – Detail of the oil feeder arrangement on the top of the cylinder.
A feature of special interest is the arrangement of three valves in the top valve chest or ‘nozzle’. These usually stand in line with the valve admitting steam to the cylinder in the middle. In this engine the ‘equilibrium’ valve, controlling the exit of steam on the return (pumping) stroke, occupies this position.
This makes a convenient arrangement for joining to the equilibrium pipe, which can be seen in front of the cylinder, but is not conducive to thermal efficiency because the live steam impinges on surfaces cooled by the equilibrium steam on its way to the cylinder. (Courtesy of The Trevithick Society)
Parkandillick Gallery 3.7 – The top of the Valve Box, governor, steam and equilibrium valves.Parkandillick Gallery 3.8 – Beautifully made, also functional and beautiful to look at.Parkandillick Gallery 3.9 – The rear of the valve box with the control arms which are controlled by the driver. Also the name T James Engineer 1853 is mounted on the chest.Cornish Mine Images 3.10 – Another image of the wonderfully preserved valve chest from the opposite side.Cornish Mine Images 3.11 – Looking up towards the beam above. The bracing rods are part of Watt’s parallel motion which kept the piston rod in a straight line .
The engine also has the sole, surviving working example of a St. Austell governor – a ratchet device which may be seen upstairs in the middle chamber.
Its purpose is to sense the length of stroke the engine makes and then to adjust the throttle valve to admit more or less steam to keep the stroke constant.
Cornish Mine Images 3.12 – A closeup of the St. Austell Governor.
So this was not a normal fitment on a mine pumping engine. But was used in the clay district to enable the engine driver to leave the engine to operate a steam hoist, supplied from the same boiler.
The invention of the St. Austell governor is credited to local engineer, ‘Jackie’ Menire. Other features include the use of hardwood pins in the valve gear to make it work more quietly. (Courtesy of The Trevithick Society)
Cornish Mine Images 3.13 – The Middle Chamber from behind the Valve Chest, the piston rises up to the beam above. Cornish Mine Images 3.14 – Finally on this page, the Middle Chamber looking down from the stairs.
