The New Zealand Railways Magazine, Volume 2, Issue 2 (June 1, 1927)
Course of Steam from Dome to Atmosphere
The course of steam from the dome of a locomotive to the atmosphere is illustrated in plate I. which shows in section, the dome, smoke box, steam chest, one cylinder and part of the boiler of a locomotive.
Steam enters the main pipe through the regulator or throttle valve (which is operated by a rod not shown) and passes along the main steam pipe until it reaches two branch pipes which lead to a steam chest on either side of the engine (see plate 2) and after passing the valves, and doing its work in moving the pistons as shown by the arrows, it passes out to the exhaust or blast pipe and out of the funnel.
In the case of the regulating valve being placed in the dome, the pipes are empty when the valve is closed, the pipe in the dome, also the long straight pipe, having the full boiler pressure pressing on their outer surfaces. If the joints marked “A” are defective, steam can blow through into the pipes and to the cylinders all the time the boiler is under steam.
If the joint in the top of the dome is defective or the valve (as indicated by the arrow marked A1) the steam issuing from the cylinder taps is dry; if, however, the joint at the bottom of the dome is defective, the steam from the cylinder taps is usually wet.
Owing to the shocks and strains which the pipes have to stand every time the regulator is opened and closed, the long pipe is apt to become weakened and cause trouble.
The joints marked B in the smokebox can blow only if defective when the regulator valve is opened. The blast pipe can show a defect only when the engine is being moved with steam on.
A large number of engines have their regulating valves in the smoke box. This is an advantage as the pipes in the boiler are not strained as are the pipes in other types of engines, for the pipes of the former always have the same inside pressure as the boiler.
The long stay nuts (a few of which are shown), the tubes and the large steam pipe joint next the tube plate, can blow, if they page 31 are defective, all the time the boiler is under steam. In an engine fitted with a super-heater the element joints can blow only when steam is turned on.
In the valve shown in Fig. 1, the whole of the back of the valve is exposed to the full steam pressure. This causes the valve to press very hard on to the steam chest port face, so that it takes a good deal of power to drive it. The pressure is relieved somewhat by the upward lift of the exhaust steam when passing under the valve, and, also, by the live steam in the port that the valve has just closed—but friction even there is very great.
Coming back to Fig. 2 it will be seen that page 32 with the frame in the back of the valve, the portion of the valve exposed to the steam pressure is small compared with the total area of the valve. Therefore, providing the frame is steam-tight, the valve is not so hard to move with steam on as with the ordinary kind of slide valve. When fitted with a frame as in Fig. 2, this type of valve is said to be balanced.
A is the valve, B the frame, C the springs, D the lip, or flange, of the frame, E the small hole or port through which any steam may escape into the exhaust port which may leak by the frame. This hole is usually about⅗ in in diameter.
The Reckless Motorist.
“Engineer Dies at the Wheel,” was the headline in a New York newspaper over an item telling of the sudden death of an engine man in the cab of his locomotive (says D. T. and I. Railroad News).
“The automative point of view which was responsible for the above is sadly out of place in this instance.
As a matter of fact, an increasing number of veteran enginemen who should have many full years of service ahead of them are dropping out because of the battering attack of numerous amateur motorists who speed along the highways of the nation at the wheels of automobiles and pile up at grade crossings disputing the right of way.
Heart failure is the award of many an engineer for long years behind the throttle. And to hold his job the engineer must pass periodically a series of the severest examinations, while the tyro on the highway needs only a little time and money to procure a license that will permit him a wide range of action, subject to only a few scattering and more or less unenforced regulations.”