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Steam Engine Details

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  • Steam Engine Details

    I came across this lovely old illustration / engraving:

    Lots of nice details in there - I especially liked the boiler feedwater pump driven from one of the valve gear eccentrics. Even the valve gear has crossheads!

    Question; there are handwheels, spindles & glands on the outer ends of both cylinders and both valve chests. What would these be for? I haven't seen this feature before, and can't think what their purpose would be. The rest of the illustration is pretty accurate, so I don't think that these will just have been dreamed up.


    All of the gear, no idea...

  • #2

    I can't see any hand wheels on the cylinders. The piston (tail) rods continue into the air pumps (?) via glands.

    There is a hand wheel on the nearest valve chest. I think we are looking at an expansion valve. This was an auxiliary valve fitted on top of the slide valve and it allowed the steam cut-off to be adjusted (without affecting any of the other valve events).

    You have noticed the two eccentrics, but there are also two rods, one attached to each eccentric. I think there will also be two valve spindles and the one valve spindle we can see is for the expansion valve. The main valve spindle is hidden. Actually, I am not exactly sure what the drawing shows in the cross head and valve spindle area!

    There were a few expansion valves invented for slide valve engines, but Meyer is commonly mentioned, invented around 1842 and still in use as long as slide valves were used.

    The hand wheel allowed the cut-off to be adjusted while the engine was running. The hand wheel worked right and left hand threads which adjusted the cut-off faces.

    All the other events were controlled by the main slide valve, just the steam cut-off was controlled by the expansion valve.

    You can probably find illustrations of this, but I can post some if you or anyone is interested.

    I think I have seen this type of valve gear fitted to an old Marshall portable steam engine (though Marshall had their own cut-off gear too).

    My apologies if you are well aware of expansion valves, and were merely wondering about the peculiarities of this particular engraving
    Last edited by Peter S; 03-16-2020, 07:29 AM.


    • #3
      Hi Peter,

      Ah yes, the cylinders indeed have rods going into those boxes. Any idea what the boxes are for? They don't look like pressure vessels. They appear to have glands on them where the extended piston rods enter.

      Hard to tell with the double eccentrics; the rods look dead parallel, as do the eccentrics themselves - almost as if one rod drives each side of the same crosshead, but that would be an expensive way of doing a simple thing. I can see how right & left threads would have made the slide valve wider or narrower - interesting way of doing it, I hadn't seen that before. If you do have an illustration, yes please.

      All of the gear, no idea...


      • #4
        The Boxes may be oil Tanks to lubricate the Engine.
        The rods ( very small) could be pump rods , OR may be tubes OR both ?
        There seems to be a sight glass at the bottom to show low oil .
        The Bevel gear on the crank is for powering the Governor, but the drive shaft between it and the Governor is not displayed ?
        Having two rods on the cross-head is weird , but not unknown. John Ericsson used two piston rods (right !) from each piston to the cross-head
        on his 1858 Vibrating Lever Patent Model seen at the Smithsonian .
        It may be seen here

        What is weird is having two different eccentrics which could bind (?)

        Green Bay, WI


        • #5
          Regarding the two eccentrics - on Meyer's valve gear the expansion valve sheave is about 90 degrees in advance of the main eccentric.

          In my opinion, the two boxes are air pumps, as found on any condensing engine. They are connected to the condenser and extract air and non-condensing gases, and probably do other things I can't remember at present! For example, some air pumps return the condensate to the hot well. Perhaps help starting the engine by contributing vacuum.

          If you do a Google search on Meyer expansion valve or similar, there are plenty of diagrams etc.

          Here is the first one I found (click and click again for full size):

          Click image for larger version  Name:	Cross_compound_engine,_plan_section_(Ripper, Heat_Engines,_1913).jpg Views:	0 Size:	173.8 KB ID:	1861990

          Click image for larger version  Name:	MR3WY0.jpg Views:	5 Size:	183.8 KB ID:	1861993
          Last edited by Peter S; 03-16-2020, 10:28 PM.