Valve gear

The steam engine control, also abbreviated to control the part of a piston steam engine, which controls the inflow of the vapor and in the outflow from the cylinder. Through the mediated means of a slide valve or switch between inflow and outflow of the steam in the steam cylinder can perform work and move the piston back and forth. The control influences the direction of movement of the steam engine by opening or closing the slide and can be valves or degree of coverage of the slider affect the filling of the cylinder and the expansion of the steam in the cylinder and determine performance and speed of the steam engine and the efficiency of their operation so to a certain extent.

A basic distinction is between the parts of the internal control and those of the external control.

Constructive target steam machine control rapid opening and closing of the steam channels to the cylinder, low vapor velocities and flow resistances, adverse small spaces as well as low heat losses of the steam flow in the internal control for the sake of a low steam consumption.

General structure, Prelude

The following control types of steam engines steam locomotives are mainly described. With regard to stationary steam engines deviating construction principles have been realized in part.

Internal control

Under internal control refers to those components that come into direct contact with the steam in and influence its input and outflow to and from the cylinder.

The central component of internal control is often a slide. This can be implemented as a flat slider ( slider shell ) or a rotary slide valve ( spool ). The slide is surrounded by the vapor-tight slide box which can be opened for maintenance and repair purposes. On the valve body partially extra valves are flanged, the commissioning of the steam engine and its low resistance as possible idle ( pressure compensator ) may be needed.

Instead of valves, but valves can also be employed.

Flat slide

The flat slider is supported on a flat surface, the sliding mirror is incorporated in the slit-shaped channels, passes back through the vapor in the cylinder and from it. The channels are connected by the slide movement in alternation with the supply of steam, and the exhaust. The pressure of the live steam from the top of the loaded slider and presses the sealing sliders mirror. It can be moved only with considerable effort, which is a significant disadvantage of the flat slide. On the other hand, it is, however, apart from weighing on him pressure, loose on the slide mirror and can stand out from the surface and thus condensing water from the cylinder drain also in completed se channels. The latter is a major advantage of the flat slide, as this damage to the steam engine can be prevented by water hammer.

Round slide

Wherein the circular or spool valve is the cylindrical configuration of the slider. Instead of the planar mirror surface of the spool occurs, the cylindrical wall of the slide bush, which is penetrated by the steam channels here. The actual slide consists of two piston bodies that are fixed depending on the design on a common slide rod or placed "on the fly ". Since the vapor pressure of the valve body is not one-sided surface - applied as in the flat slide, but acts on both outer surfaces to spool without great effort and regardless of the vapor pressure can move relatively freely. However, piston valve systems can in a water hammer concluded vapor channels not release as flat slide by " lifting " and must therefore be provided with additional fittings such as cylinder safety valves or rupture disks.

The spool is the most widely used design of the internal control system and can be found in several types with European steam locomotives. A distinction is usually fixed piston valve, where the pressure compensation for idling of the steam engine is made possible by external valves of combined pressure compensated piston valves. The most famous of which are types of Karl Schultz- slide ( Nicolai piston valve ), the Müller- slider and the slider Trofimoff.

Valve control

In place of the relatively heavy flat or round slide smaller and lighter valve can be used to control the ingress and vapor outlet, similar to those used in internal combustion engines. In particular are known the Lentz- control and the Caprotti control. The valve actuation can be done via back and forth moving cam rods and through centrally or eccentrically oscillating or even rotating camshaft.

While mild disc valves must open against the vapor pressure, double seat valves (pipe valves) and piston valves are pressure balanced. Valves offer advantages over slider controls the advantage of great in-and outlet cross-sections, less harmful and less throttling rooms. They are therefore suitable for fast running.

Lentz control

The Lentz control is named after its developer, the engineer Hugo Lentz.

Lentz control with vertical valves and valve actuation via cam rods

In the most common Lentz- valve control system are located above the steam cylinder four standing in line Valves. The two outer valves serve the steam outlet, the two inner valves to the steam inlet. The valves are manufactured as double seat valves made of mild steel. Screwed onto the hollowed valve stem, the valve actuating head. This radially guided the cam rod with the valves operated lift curves, the spring- loaded pressure valve head rolls over glass hard hardened rollers on the reciprocating cam rod from. The movement of the cam bar, parallel to the piston, is produced by an ordinary steam locomotive controller according Heusinger but enlarged in the interest of rapid opening stroke, the controller is, therefore, to use also as a common control valve.

Because of the pressure spring -loaded valves are required to protect the cylinder against water hammer no special facilities. Further, by a probe device in which by means of compressed air or steam, the valve stem head can be lifted off from the cam bar and is a permanent valve opening possible, a particularly lightweight idling of the engine can be achieved. As an advantage over the piston valve control was also considered that the valve seat without expensive machine tools can be reground and accounted for the tendency to leak stuffing the spool.

Lentz control with vibrating centric camshaft

In this embodiment, the Lentz- valve control, the valves are not by a cam rod, but a parallel to the axis lying vertically oscillating (ie not constantly corotating ) camshaft operated. The valves are arranged here lying on the steam cylinder. The camshaft is driven by the drive axis by means of rods and a crank counter.

The Lentz control with vibrating centric camshaft initially found in stationary steam engineering, then as well as in hot steam composite Locomobiles the company Lanz use. A first use in locomotive building was carried out in Italy in 1906. The advantage of this design in particular was the simpler manufacturing of rotating components.

Lentz control with eccentric vibrating camshaft

In contrast to the aforementioned camshaft design of the Lentz- valve timing overlap with this valve spindle axis and cam axis is not, but go at a certain distance, so eccentric, past each other.

External control

When external control is any mechanical transmission parts, such as levers, cranks, cams, or other transmission elements that move the components of internal control. The control is derived directly from the motion of the controlled steam engine piston. By varying the stroke of the slide lever ratios and thus the degree of filling, and even the direction of rotation of the steam engine can be varied. Here, then one speaks of a slide control. Valve controls are regulated by adjustable or movable cam or cams.

Before convertible and adjustable controls have been developed, the steam locomotive could be controlled only with the steam controller for reversing the direction of travel had parts of the engine to be changed in a complex " hand work", as will be apparent from the description of Robert Stephenson in 1831 built locomotive John Bull.

Since the basic structure of the outer control is independent of the internal control, control types are named according to the structure of the outer control.

Control types

Some types of vapor control systems are:

• Stephenson valve by Robert Stephenson ( UK, first half of 19th century )
• Hackworth control of Timothy Hackworth (United Kingdom, first half of 19th century )
• Control by William T. James on a locomotive of the Baltimore and Ohio Railroad, ( U.S., 1832)
• Gooch control of Daniel Gooch ( UK, 1843)
• Allan Trick or control, by Josef Trick ( Germany, mid-19th century )
• Heusinger control ( engl. ' Walschaerts gear' ) of Egide Walschaerts (Belgium, 1844) or Edmund Heusinger von Waldegg ( Germany, 1849)
• Joysteuerung by David Joy ( UK, 1879)
• Gölsdorf'sche angle lever control ( Austria, late 19th century )
• Baker - control (USA, 1903)
• Caprotti - valve control of Arturo Caprotti (drive through rotating shafts, Italy, 1921)
• Gresley control of Nigel Gresley ( UK, first half of 20th century )
• O & K Patent control ( Germany, first half of 20th century )

Control arrangements

In Dampflokomotivbau the arrangement between internal control and external control is differentiated with respect.

As internal control is referred to, that the control linkage together with the slide boxes located in the interior between the driving wheels such as in the Prussian G 3 Somewhat less frequently, the drive rod assembly can be located in this area. Frequently, but not necessarily with it an exterior frame construction is connected, which leaves enough space for the internal control, such as in the MÁV IIIe.

When external control is meant that the control linkage is outside, along with the slide boxes next to the driving wheels. In most cases, the cylinder and the whole traction rods are arranged externally, as the above images show control it. Occasionally, but can also watch the cylinders and rods are in the interior, while the connecting rods are placed outside, for example, see kkStB 9