Variable Valve Timing - 1886
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  1. #1
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    I was intrigued by this unusual(?) type of valve gear on a steam engine. It can be difficult to figure out how the cut-off of steam admission valves is varied, but this is simple and ingenious.

    Poppet valves, roller cam followers, and variable geometry inlet cams whose axial position is determined by the governor.

    The engine is at my local steam museum at Westonzoyland.
    It was patented by the engine maker, a local firm called Wills, of Bridgwater. It was a small general engineering company, who also made special purpose machines for the local brick and tile industry, and things as mundane as cast iron signposts. I think they were connected with W D & H O Wills, the Bristol tobacco company, whose cheap and thin Woodbine cigarettes, in affordable packets of 5, doubtless lured some UK members into the habit at a very early age. As far as I know, Wills Engineering is still in business. Several years ago I ordered some hollow stainless steel ‘O’ rings from them, for use on a high pressure steam system. The rings were rolled from tube and butt-welded, and silver plated. They were filled with pressurised gas, but they wouldn’t tell me how they achieved this.






    Governor:-



  2. #2
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    Looks similar to the reversing gear on some marine diesels, where the camshaft was slid to engage the reverse cams.

    Is that a saddle key on the short cam?

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    Asquith,
    Thats pretty cool! I guess the cam shaft is drilled and has an internal rod connecting the sliding cam to the governor?
    It looks like you got someone to hold the weights up for one of the shots?

    I am trying to remember how the cams worked on the very first Mercedes engines (ie c.1901-03). These engines had very little rev range (probably around 1200rpm max from memory), no throttle to speak of. I think the cam moved longitudinally to control valve lift, and so give some control over engine power. Not a very good system.

    Gas-filled rings - on another forum, someone mentioned using what I think were called 'Coopers' rings to seal the cylinder heads on a racing engine. I think these were nitrogen filled tubes. Could be wrong....

    I see you have been posting some great photos lately - always interesting to me.

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    Hi Asquith! Thanks for sharing the photos. Ames Iron Works in Oswego, New York used a similar set-up for their vertical Unaflow steam engines. These were 3 or 4 cylinder engines similar in appearance to a modern marine diesel. The Ames set up was totally enclosed, the governor was on
    the end of the camshaft. I never get tired of seeing how the various manufacturers engineered variable cut-off gears for their engines. -JM

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    Asquith, we have noticed that you folks from the British Isles have some of the best antique machinery. You folks raise the whole tone of this group!! [img]smile.gif[/img]

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    Interesting machinery Asquith, as usual.

    The gas filled sealing rings have always been known as Wills rings in the UK, though Coopers does sort of ring a bell, perhaps they were the American producers ?

    My old Wasp sidecar motocross engine used Wills rings for the head to barrel joint, if installed with appropriate care they proved quite reliable. If I remember correctly their usage for internal combustion engines originated with the Coventry Climax / Hillman Imp racing engines.

    regards

    Brian

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    Any one seen or heard of a TWilley steam valve adjusting device,was a small cylinder place a paper in it and a lead pencil made a mark on the paper as the cylinder turned by a device hooked to a turning shaft never seen it used but the old man that explained it was a stationary steam engine mechanic probably in his 80s

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    I was thinking the same thing J tiers was, thsoe old reversible engines are something I could was operate for hours on end.

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    Asquith:

    The mechanism shown on that engine is the same that Harris used to control the amount of water applied to the plate of an offset printing press by it's dampening system.

    I have a bit of real time experience with that type of cam set up.

    It is simple and cheap and does a good enough job for most purposes.

    The cams are subject to localized wear making the system jumpy if it has been run in one position for a long time and then wants to change.

    George Corliss's claim to fame was the variable admission valve timimg that was independent of the exhaust valve events.

    To accomplish this, Corliss had to use separate valves for admission and exhaust. Corliss's work was circa 1849.

    Subsequent mechanisms had the main objective of getting rid of the drop cut off links and dash pots charachteristic of the Corliss gear.

    The device mentioned as the steam valve adjuster is called the steam engine indicator. It plots a graph of cylinder pressure vs. piston position.

    The thing was invented by James Watt and later improved by the rotating paper drum and the pantograph pencil linkage (Watt parallel motion) between the steam piston and the scriber.

    Steam engine indicators are used while the engine is running. It is the mechanical analogy of the electronic oscillograph or oscilloscope. The instrument takes measurements of changing values in a dynamic situation.

    Variable inlet valve timing has limited application to internal combustion engines.

    Nordberg "Supairthermal" engines of the 1960's used it in order to more effectively match the egine operating characteristics with those of it's turbo supecharger. Of course, these were big four cycle egines.

    Cimmins tried variable inlet valve timing on some of it's truck engines.

    In both cass, the complexity of the valve gear militated against both the first cost of the engine and the engine's overall freedom from abjdutment and repair.

    Nowadays the variable inlet valve timing seems to be used in the efforts to reduce an engine's exhause emissions rather that to further thermal efficiency.

  10. #10
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    Asquith,

    It seems a bit odd, but here I am along way from home, and I have with me an account of this engine, in fact it is apparently the only survivor of W & F Wills of Bridgwater, Somerset. This engine used to drive a pugmill in the brick and tile works of Majors of Salmon Parade, Bridgwater.

    This article appeared in a 1985 ISSES bulletin by Chris Allen, and is titled 'W. & F. Wills patent valve gear - misfit or prophecy.

    It is an interesting article that examines why there was a need for expansion control (ie variable cut-off) by governor.

    There were ways of varying cut-off, but they were fixed or manually adjusted (Meyer etc).

    There were also governor controlled throttle valves.

    Neither of these methods meet the needs for engines running under varying load while remaining efficient.

    The author then comments on the size of engines - how it was in the larger sizes that one expected to find seperate steam and exhaust valves and sophisticated control gear.

    The author then examines the Wills patent of 1885. The engine in the museum is a close copy of the patent, though built in 1896. It has 9" bore and 1'6 stroke, and two steam and two exhaust valves of the double beat type arranged in pairs at opposite ends of the cylinders.

    He then asks - was this engine a misfit or prophecy?

    "At first glance this valve gear appears to be misplaced on small engines. To my mind it appears too complex and costly to be an economic proposition when fitted to a small, basic, non-condensing steam engine. However, at the same time one could regard it as being the forerunner of the modern high efficiency drop valve engine, with widely seperated steam and exhaust ports; on the other hand, it could be perhaps be regarded as an antecedant of the valve gear of the modern internal combustion engine. In reality it is unlikely to have had any bearing on the development of any subsequent types of valve gear and is best regarded as an evolutionary cul-de-sac, but with some features reminiscent of these more sucessful types.

    I feel that I can make these contentious remarks, as the continental manufacturers, led by Sulzer, were already shaping the modern drop valve engine, whilst the divergent technology of the internal combustion engine was already becoming established and its proponents are unlikely to have been influenced by the products of a relatively obscure Somerset firm."

    The patent also had some variants on the valve lifting gear - one was the cam acting directly on the valve spindles. (The valve spindles being extended down through the bottom of the valve chest). Just like an ohc engine.

  11. #11
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    Peter,

    Thanks for the information, and for bringing facts 12,000 miles which have broadened my knowledge on something made 8 miles away! I know little about Wills, but I do know that they made special purpose machinery for the local brick and tile industry in the heyday of fiddly earthenware finials. I’ve seen a picture of a machine they made for extruding V shaped clay ridge tiles. Wills was a very small outfit, but evidently one with a disproportionate amount of skill and ingenuity.

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    Nice little engine Asquith, Does the cam operated valve gear make much noise when operating-- A clip - clop sound like a little horse maybe? Or is it like some of the big Ruston or National horizontal diesel oil engines the valve gear was fairly quiet considering the style of engine, Any chance of getting the volounteers to give her a spruce up & polish?

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    Mac,

    The engine is extremely quiet, the only noticeable sound being a slight ringing sound from the camshaft bevel gears occasionally when the backlash is taken up.

    I was sprucing it up today, but I kept stopping to study and admire the workmanship.

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    Talking

    Thanks Asquith, sounds a nice little engine with most intriguing features Get on with the cleaning, your not there to stand and dream! If i visit will will i be given a handful of cotton waste?

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    Cotton waste? Bring your own! We're short of cleaning materials. Bring some firewood as well, for the boiler, if EasyJet will let you take flammable items on the Bristol flight.


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