Valves
Steam regulator used in Newcomen's steam engines
In Newcomen's engines, the regulator is placed in the boiler itself, or in the steam box beneath the cylinder. It has two pieces, one of which is movable and the other fixed. The movable component is a flat brass plate in the shape of a fan, whose upper surface perfectly fits the entire circumference of the steam pipe's orifice and completely prevents steam from entering the cylinder. The regulator can be turned aside by a lever fixed on the upper end of the axis to uncover or open the passage
The orifice of the steam passage is formed in the fixed part of the regulator, which is a brass plate of a sectorial shape. It is fixed into an opening in the top plate of the boiler, or of the steam-box, by several rivets. From the upper side of this fixed brass regulator plate, the steam pipe rises for a few inches and is united to the iron part of the pipe, which projects downward from the bottom of the cylinder. A plate of sheet lead is wrapped around the outside of both pipes to cover the joint and is bound fast by a lapping of small cord. The two parts of a steam pipe are made the same size on the outside, and a piece of canvas soaked in white lead and oil is applied immediately on the pipes beneath the sheet of lead. This was the universal practice for many years, and despite that the vibrations of the cylinder rendered it leaky so often, the attendant could always renew the cloth and cord.
The orifice of the steam pipe beneath the fixed brass plate is not circular, but sectorial, and the regulator is borne upwards by a spring to keep it in close contact with the fixed regulator plate. The lower surface of the regulator has a protuberance in the middle to rest on a spring, which presses it towards the steam pipe, so that it applies very close. [Farey, page ]
Mr. Curr also describes an atmospheric engine with two stop-valves that rise and fall perpendicularly into conical apertures or seats for the alternate admission of steam and cold water into the cylinder instead of the regulator and injection cock. This is the modern form of construction for such engines and will be described in its proper place, because they are improvements adopted from Mr. Watt's engines, which will be described in the fifth chapter. [Farey page 211]
Watt's improvements
In his first essays at Kinneal, Mr. Watt employed cocks and also sliding valves, such as the steam regulator of the old engine, but he always found them to become leaky after a short time. This is not surprising when we consider that they were always perfectly dry and kept boiling hot. He was therefore obliged to change them all, except for the spindle-valves, which, being truly ground and nicely fitted at first, were not found to be so liable to get out of order. The spindle valves were then a new application to steam engines, except for the safety valves in the boilers; they were also called puppet-clacks or button-valves.
The spindle-valve is a flat circular plate of bell-metal, with a round iron spindle passing perpendicularly through the centre of it, and projecting above and below it ; this valve is very exactly fitted by grinding, into a circular seat or aperture, which forms the passage that the valve is required to open or shut, and the valve being conical on the edge, fits like a plug into the aperture of the seat, which is also conical, so as to entirely stop the passage when it is let fall ; but when the valve is raised up above, or out of its seat, a free passage is allowed on all sides of it. The spindle of the valve is supported in two sockets, one above the aperture and the other below, to retain it in its exact perpendicular direction and cause it to drop exactly into its place.
The spindle valve
The "lift-tenter," a device used to control the sluice of water mills, was reportedly proposed by Mr. Clarke of Manchester as a way to control the motion of the steam engine. James Watt had to modify the much bigger "lift-tenter" so that he could apply it in his steam engines. [Robert Scott Burn, "The Steam Engine - It's history and Mechanism ", London, 1854, page 51] ;
The spindle-valve is a round, flat plate of bell metal with protrusions above and below that is perpendicularly pierced by a round, iron spindle. The valve is extremely carefully installed by grinding into a circular seat or aperture that creates the passage that the valve must open or close. When the valve is raised above, or out of its seat, a free passage is provided on all sides of it. But, when the valve is lowered below, or in its seat, the passage is completely blocked by the conical edge of the valve, which fits like a plug into the aperture of the seat, which is likewise conical. Two sockets, one above the aperture and one below, support the valve's spindle.
The spindle or tail of the valve b continues upward and is formed into a small rack. This works into the teeth of a quadrant e, which is moved by the spanner or lever d, worked by the plug-frame of the engine. [Farey]
Murdock's socket valve
Following Mr. Watt's retirement from the industry, Mr. Murdock used this construction for large house-built steam engines for factories for the first ten years that he oversaw the Soho factory. This engine's action is identical to that of Mr. Watt's original rotative engine. Instead of using a sun and planet wheels, a simple crank and flywheel are used to generate rotation. The main structural variations are found in the nozzels and the equipment used to open the valves. An eccentric circle fixed to the crank's axis generates motion that opens and closes the valves. The valves are opened and shut by the motion derived from an excentric circle fixed upon the axis of the crank.This motion actuates upright rods 10,13, which control the opening and closing of a steam valve b and an exhaust valve h contained in a valve box. Murdock returning from Cornwell to Soho had already devised two machines with these socket valves, which were used in Soho in May 1799 and dispatched to a client in late 1799. [H.W. Dickenson p. 189]
The steam valve b and the exhaust valve h are fitted into brass seats within the valve box thus separating a valve box into three compartments. A branch from the valve box's middle compartment c extends into the top of the cylinder E. The exhaust valve's h spindle travels up through the steam valve's b spindle, which is hollow like a tube for that purpose, and then travels through a stuffing box, which is situated on top of the steambox cover. Hemp is used to make tight junctions in the stuffing boxes around those tubes. These stuffings stop steam from escaping or air from getting in. In order to open the passages through the valve seats, the valves b, h are raised by suitable short levers 18, 19, which engage with the spindles on the outside of the boxes. The two valves b, h can be opened or closed independently of one another.
The exhaust valve's h spindle is held in place vertically by its upper end being received in a fixed guide, and its lower end is held in place by a socket in the valve seat's center. The valves will rise and fall into their seats very accurately because the spindles are guided at their upper and lower ends in this way.
While the rod 13 is obscured by the rod 10 in the above drawing, the 3D view shows that the rod 10 is connected to the exhaust valve lever 18 and the rod 13 is connected to the steam valve lever 19. The working gear shown in the lower part is still intricate.
