Inglis and Spencer's Corliss valve releasing gear
The firm of Hick Hargreaves of Bolton built many large steam engines using Corliss valves, their 'in house' design of releasing gear was named Inglis and Spencer (or Spencer - Inglis - it depends where you look and who you talk to !) after its two designers. Their engines operated either with a single eccentric and wristplate, driving both inlet and exhaust valves, or two separate eccentrics and two wristplates, one driving the inlet and the other the exhaust valves.
Fortunately two of these engines still survive, one at Forncett (single eccentric) the other at Gurteens Textile Mill in Haverhill - a two eccentric design.
CAUTION
Ensure it is OK to run an MSDOS program at this point - otherwise download it to run later in an MSDOS window.
Here follows some pictures and a description of the action of this valvegear, alternatively you could take the easy way out and look at either this Inglis and Spencer Demo program or this fully configurable valvegear simulation program written specially for this website by Charlie Dockstader of California, USA - this program shows the double eccentric version as configured but you can simulate the single eccentric version by changing the defaults to these parameters :
4B1=0.95 4B2=240.0 4B3=13.03 4C1=0.95 4C2=240.0 4C3=13.03 4D2=0.0 4E1=-0.70 4E2=0.0 4H1=0.63 4H2=0.63 4P1=6.7 4P3=2.25 4P4=2.25 4S1=0.16 4S2=0.16
To run select G when the MSDOS window opens, other options letters are highlighted in the text, to alter the governor position while the graphic is running use shift and the < or > keys
If you refer to the drawings you may be able to see how it all works, (Note that only half of the complete assembly is shown) The eccentric rod A moves left and right, driven by the engine crankshaft, it is linked to a pin at Y and this causes the wrist plate B to rotate so that point D moves between D and Z.
The inlet valve spindle H can oscillate between the open and closed positions as shown, the valve opens as the wrist plate rotates anti clockwise with pin D moving away from position Z, this pulls the linkage O to the left which in turn rotates the valve spindle. The linkage between J and S compresses spring T as this happens, V is a dashpot (which is an air cylinder) and S is a piston, the air flow out of the cylinder is controlled by a valve U
The pallets arms P are spring loaded and try to spring towards each other, there are four hardened steel pallets two on P and two on Q which when engage cause both sets move together.
N is the pallet releasing cam which is controlled by the position of M, an adjustable linkage between M and L which is controlled by the governor rod m, attached to point K and through geared quadrants X which pivot on shafts W (giving an equal action to both ends of the cylinder), the position of M will vary depending on the position of the governor linkage (which varies with the speed of the engine) if the engine is over speed then point M will move to the right if too slow it will move to the left.
The cam N forces apart the spring loaded pallets P, when these release the pallets on Q the spring T will be free to rapidly shut the valve by pulling J to the left, the speed this closes the valve is controlled by the rate at which air compressed by piston S can escape from the dashpot V through valve U. When M is to the right (i.e. the engine is overspeeding) cam N releases the valve earlier, not allowing steam into the cylinder for so long, if M is to the left (the engine is underspeed) then steam is allowed in for a longer time until the engine is 'on speed' again.
When the wristplate rotates clockwise again the pallets on Q slide under the pallets on P, which spring back and they re engage, ready for the next operation.
The exhaust valves rods F are driven from pins C and are opened and closed as shown on the lower right.
