Piston rod

“ When the piston was raised by the action of the steam, a vacuum was produced by the condensation of the steam in a cold-water tank placed underneath the engine, on which the piston was again forced back by the pressure of the atmosphere. The motion was communicated to the wheels by rack-rods connected with the piston-rod, which worked on each side of a drum fixed on the hind axle, the alternate action of which rods upon the tooth and ratchet wheels with which the drum was provided producing the rotary motion. ”

“ Unless the piston rod is kept tight in the cross-head, there is liability of a bad crack. A small strain will bring the piston out of the cross-head entirely, when the chances are you will knock out one or both cylinder-heads. If a nut is used, there will be the same danger if it comes off. ”

“ When piston rods are threaded into the cross head, or into the piston, the threads are made an easy fit, and taper seats or split hubs secured by clamping screws are relied upon to keep the rod true to the cross head or piston, it being found that the screw alone cannot be relied upon for this purpose. ”

“ The cover, when bolted on, forms a part of the cylinder; the piston rod is cast solid with the piston, and is made sufficiently large at its outer end to receive the tool. These two parts constitute an engine, and with less than one fixed and one moving part it is obviously impossible to develop power in a machine by the action of an elastic fluid. ”

“ The piston-rod, D, passes through a sleeve in the cylinder cover, I, which should be long enough to steady it and act as a guide, and is limited in its upward motion by the collar, d. E is a conical exhaustvalve, seating upward against the bottom of the piston, G. F is the steam-valve, also conical, and seating upward, containing within itself the tail of the exhaust-valve, E; such an amount of motion being permitted between the two that the steam-valve, F, will be raised to its seat, and the exhaust-valve, E, be opened as the piston approaches the upper end of its stroke. ”

“ The space for the stuffing or packing is marked C. This is filled with lamp cotton, and when the gland is [134] screwed down the cotton is compressed, so that it makes a steam-tight fitting for the piston-rod to slide in. The hole for the piston-rod is shown through the centres of both sections. As before explained, the gland on the left is secured by two screws shown in the section; it is fitted into a plain cylindrical hole. The other gland is threaded to screw direct into the cylinder cover, which is tapped to receive it. The first method is the one always employed in large engines. ”

“ It will be readily seen that as the disc revolves it gives a reciprocating movement to the rod, causing the slide valve to which it is connected to open and close the ports in the cylinder, and the object in attaching the eccentrics to the crank shaft is that the piston rod and valve rods may have an equal and corresponding action, which it will be understood is absolutely necessary. ”

“ Thus, cross-heads are frequently fractured by main-rod connections pounding; and weaknesses, that ultimately bring crank-pins to disaster, originate in a similar way. A loose piston-key is liable to crack the piston-rod, if it does not give trouble by jumping out. Loose guides have a tendency to spring piston-rods, and throw unnecessary strain upon them. Pistons lined out of true, are dangerous for the same reason. A pump-plunger working out of line, or badly secured in the lug, throws a distressing load upon the cross-head. ”

“ Cast-iron arms, if bulky enough to be safe against external blows, are awkward in shape. The sectional area necessary for any arm depends upon the means provided for preventing a sidewise strain on the lever, due to rotation of piston or friction of its connection to piston rod. The spool or crosshead on the piston rod should be so designed that no sidewise strain can be thus produced on the lever. ”

“ To the connecting rod was attached a rather ordinary ringed piston, over which was fitted a free, ringless piston, machined to fit closely the cylinder bore. This floating piston could move freely a distance equal to the compression space. The intention was that on the intake stroke, suction would open the intake valve, which had no positive opening arrangement, and draw in the mixture which then was compressed as in a regular Otto engine. ”