Water Engines: Page 4

The Schmid engine was of Swiss origin.

This engine is not identified in the source, but it clearly corresponds with the drawing below. Having said that, there are some intriguing differences; the flywheel of this drawing has six spokes instead of four, and so on.

As with the Ramsbottom, the valve arrangements are very simple, probably because there is no need to allow for any variation in cutoff. The ports are are in the curved part at the bottom of the cylinder, once more covered and uncovered as the cylinder(s) oscillate. Water comes in through the pipe under the cylinder, and exhausts out to the left.

The purpose of the three small fittings on the top of the cylinder is obscure. The two at each end are most probably some kind of relief valve, but the larger one in the middle is a puzzle. If it is a lubricator, what induces the oil to flow inwards against all that water pressure?

From The International Library of Technology, Hydraulics Volume, 1920. Pub Scranton International Textbook Co.

Not brilliant picture quality, I'm afraid, but it does show (sort of) some extra details.

One common factor in these engines is the small throw of the crank compared with steam engines. This is presumably because of the greater piston force produced by hydraulic pressures of 800psi, much greater than the common steam pressures of 50 - 150 psi. As there was no expansion, this pressure was also maintained for the whole of the piston stroke.

The structure at top left is probably an air chamber to reduce shocks as the amount of water drawn from the supply main varies.

From Knight's American Mechanical Dictionary, 1881.

Probably a unique photograph. This is one of two preserved Schmid engines at the Altes Wasserwerk pumping station in Rothenberg, which from 1902 until the 1960s supplied the villages of Rothenberg, Ober-Hainbrunn, and later Kortelshütte with water.
Power water comes from 40 metres above the pumping station, and water is pumped up 280 metres from the Gammelsbachtal valley to the Rothenberger High reservoirs.

The engines were manufactured by the Maschinenfabrik Schmid in Zurich. The first engine-pump unit was installed in 1902, the other in 1904, allowing alternate operation and thus a continuous water supply during maintenance work and repairs.

Power water comes in through the grey pipe at bottom right, and exhausts through the black pipe to the extreme right. Note the air chamber at upper right. As usual, the two cranks are set at 90 degrees.

Each cylinder has two associated handwheels; I think, but have yet to confirm, that these control the tightness of the packing on the two cylinder trunnion bearings. The aim is to allow a small amount of water leakage- enough to lubricate the bearing without excessive waste of water. The piston-rod gland is a stuffing-box packed with knitted yarn impregnated with tallow.

The copyright status of this image is uncertain. I have tried to contact someone at Rothenberg, to no avail. If anyone feels I have infringed their rights then please let me know at once. I'm sure we can work something out.

At least, I'm pretty sure it is. The two pipes are labelled in German "suction pipe" and "pressure pipe" which sounds as if it was a pump. However, in every other respect it looks like a single-cylinder Schmid engine.

Note the adjusting handwheel on the lower trunnion bearing. The upper bearing is shown in section so only the spindle of the handwheel is visible.

Once more, not brilliant picture quality, I fear.

This description is given in Knight's American Mechanical Dictionary, 1881

"The valve shown at B C is balanced and self-packing. The induction-port a is located at one end, in one of two transverse discs b at the end of the valve. These fit closely the interior of the valve-chest c, and are connected by a flat plate d. A hollow trunnion e admits the water, which flows in the direction of the arrows into the valve-chest. A curved plate f, having openings g serving as eduction-ports for the valve, diffuses the pressure. An orifice h, opposite the hollow trunnion admits water back of the disk nearly balances the end-pressure of the valve, only sufficient excess of pressure being allowed to pack the washer which keeps the joints from leaking. This pressure may be relieved, if necessary, by means of the set-screw i. An auxiliary pipe and valve k, opened by means of a separate eccentric, are arranged to give an additional supply of water when the piston has traversed one fourth of the length of the cylinder, so as to equalise the motion of the crank."

The last bit is rather opaque, but may refer to an attempt to minimise variations in torque on the output shaft. It is also not too clear where the valve goes on the main picture.
Note the importance of making the valves balanced when using such high pressures; otherwise operating friction would be excessive.

From Knight's American Mechanical Dictionary, 1881.