Steam valve

“ In the simple form of valve that appears in Fig. 24, the valve faces are just wide enough to cover the steam ports. If the eccentric is not square with the crank, the admission of steam lasts until the very end of the stroke; if set a little in advance—that is, given lead—the steam is cut off before the piston has travelled quite along the cylinder, and readmitted before the back stroke is accomplished. Even with this lead the working is very uneconomical, as the steam goes to the exhaust at practically the same pressure as that at which it entered the cylinder. ”

“ When the engine is to be stopped, shut the injection valve and secure it, and adjust the tappets so as to prevent the exhausting valve from opening and to allow the steam valve to open and remain open, otherwise a partial vacuum may arise in the cylinder, and it may be filled with water from the injection or from leaks. A single acting engine, when it is in good order, ought to be capable of going as slow as one stroke in ten minutes, and as fast as ten strokes in one minute ”

“ The mechanical valve-gear does not often get out of order, but sometimes the unexpected happens. The shop man may not have properly set up the nuts on the valve-stems; or may have fitted the distance bushings between the shield plates too closely; the superheat of the steam may distort the steam chest slightly and produce friction that will interfere with the regulation. If any of the valve-stems should become loose in the cross-heads they may screw themselves either in or out. ”

“ Many other ingenious forms of expansion valve-gear have been invented, and several have been introduced, which, properly designed and proportioned to well-planned engines, and with good construction and management, should give economical results little if at all inferior to those just named. Among the most ingenious of these later devices is that of Babcock & Wilcox, in which a very small auxiliary steam-cylinder and piston is employed to throw the cut-off valve over its port at the instant at which the steam is to be cut off. ”

“ The cut off valve has a travel considerably beyond the edge of the steam passage after the valve is closed, and this has one advantage, that the valve is less liable to leak, and to this must be added the loss from the friction of this moving valve, and moving too in opposition to the main valve. In our perfect valve, as we outlined it, the valve does not move after the port is closed. The exhausting functions of the valve are very good, giving a quick opening and a full opening, because this opening occurs when the eccentric is moving its fastest. ”

“ The use of the steam expansively is to stop its rush to the cylinder when the piston has only partially accomplished its stroke, leaving the remainder of the [22] stroke to be driven by the expansion of the steam. In early engines the steam was admitted by conical valves, worked by a rod from the beam. Murdock, we may add in parenthesis, is believed to have invented the slide-valve which came into use as locomotives were introduced, and of which there are now numerous forms. The valve is usually worked by an “eccentric” rod on the shaft of the engine. ”

“ The chest of the blow-through valve is very commonly cast upon the valve casing; and in engines where the cylinders are stationary this is the most convenient practice. All engines, where the valve is not of such a construction as to leave the face when a pressure exceeding that of the steam is created in the cylinder by priming or otherwise, should be provided with an escape valve to let out the water, and such valve should be so constructed that the water cannot fly out with violence over the attendants ”

“ The aim of many engineers has been to take advantage of these matters by using the valve with 90° angular advance of eccentric ahead of crank, for the admission, release, and compression of the steam, and provide another means of cutting off, besides the one already referred to, viz., cutting off the supply of steam to the chest, and overcome the objection in this one of large clearance spaces. This is done by means of riding cut off valves, often called expansion valves, of which, perhaps, the most widely known types in this vicinity are the Kendall & Roberts engine and the Buckeye. ”

“ Double ported valves are employed in some cases to increase the admission of live steam to the cylinder, and in others to increase the exhaust openings also. The effectiveness of a double ported valve is mainly valuable at the beginning of the stroke, and is especially valuable in cases when the travel of the valve is diminished to hasten the point of cut off, because in such cases the outer edges of the valve do not open the steam port to its full width, and a single port is apt to wire draw the steam. ”

“ In all engines, a considerable quantity of steam is allowed to escape from the safety valve. Whenever the vessel stops, the steam, which would otherwise be taken from the boiler by the cylinders, passes out through this valve into the atmosphere. Also, whenever the cylinders work at under-power, and do not consume the steam as fast as it is produced by the boiler, the surplus steam escapes through the valve. ”

“ By this means the shaft, K, is relieved of all side pressure. The exhaust-port, which is very large and relieves all back pressure, is shown at D. The pistons and disks are made to balance at the speed at which the engine is intended to run. The steam-valve, for which patent is pending, is new in principle. It has a uniform rotating motion, and, like the engine, is steam and mechanically balanced. ”

“ The first valve will close the steam to the engine and the second will control the flow of steam to and from the manifold. These valves can be operated by hand from a platform located on the wall inside the engine room, or they can be closed from a distant point by hydraulic apparatus. In the event of accident the piping to any engine can be quickly cut out or that system of piping can quickly be disconnected from the compensating system. ”

“ A.--The best construction of slide valve appears to be that adopted by Messrs. Penn for their larger engines, and which consists of a three ported valve, to the back of which a ring is applied of an area equal to that of exhaustion port, and which, by bearing steam tight against the back of the casing, so that a vacuum may be maintained within the ring, puts the valve in equilibrium, so that it may be moved with an inconsiderable exercise of force. The back of the valve casing is put on like a door, and its internal surface is made very true by scraping. ”

“ The small cylinders on top of the steam chests are for the purpose of guiding the upper ends of the valve spindles, and are fitted with pistons having steam beneath, the space above being in communication with the condenser. The steam pressure on the piston supports the weight of the valves and valve gear.
The friction of a slide valve may be relieved or reduced by excluding the steam from its back, which is done by various means, such as by a ring cast on its back and working steam tight against a plate held independently of the valve. The interior of the ring should be open to the exhaust. ”

“ A safety valve should always be fitted to a steam boiler. One of the spring valves has been illustrated in the chapter treating of the small oscillating engine. The lever safety valve is more certain in its action, especially in model work, and is better adapted for stationary purposes. A weighted lever is of no use to a locomotive or marine boiler, as the motion of travelling would disarrange the gear. The safety valve of every engine should be tested frequently, to make sure that it does not stick in its place and that all works perfectly free. ”

“ A. A vacuum relief valve is usually located on the steam chest or the live steam passage to the chest and opens when steam is shut off and engine drifting, allowing atmospheric pressure to pass into the steam chest, closing when working steam. A cylinder relief valve is a pop valve screwed into the cylinder head and set at high enough pressure so it does not open in ordinary service, but will open to allow water to pass out when the exhaust port is closed by valves; or on compound engines when the pressure in the low-pressure cylinder gets too high. ”

“ Although steam leakage through the valves of a turbine may not materially affect its steam consumption, unless it be the leakage through the overload valve during a run on normal full load, a thorough [119] examination of all valves is advocated for many reasons. In a turbine the main steam-inlet valve is usually operated automatically from the governor; and whether it be of the pulsating type, admitting the steam in blasts, or of the non-pulsating throttling type, it is equally essential to obtain the least possible friction between all moving and stationary parts. ”

“ Now if your engine is all right, you can run the pressure up to the point of blowing off, which is from one hundred to one hundred and ten pounds. Most new pop valves, or safety valves, are set at this pressure. I would advise you to fire to this point, to see that your safety is all right. It is not uncommon for a new pop to stick, and as the steam runs up it is well to try it, by pulling the relief lever. If, on letting it go, it stops the escaping, steam at once, it is all right. If, however, the steam continues to escape, the valve sticks in the chamber. ”

“ In the Richardson valve, all the steam which escapes into the open air escapes from the huddling chamber, through a stricture which is smaller than the aperture at the ground joint. In the defendants' valve, the valve proper has two ground joints, one at the inner periphery of the annulus and the other at its outer periphery, and only a part of the steam, namely, that which passes through one of the ground joints, passes into the huddling chamber and then through the stricture, the other part of the steam passing directly from the boiler into the air, through the other ground joint. ”

“ Some of the most important details of a steam engine are those of its valve gear. The simplest form of valve is that known as the plain slide valve, and as nearly all others are a modification of this, it is essential that the designer should first familiarize himself with this particular type of valve in all its details of operation. ”

“ The right valve saves fuel, because unnecessary amount of pressure is not needed to force out air, the right valve copes with dirt and dust, prevents floods, requires no adjustment. Air and steam units cannot mix, the valve releases the air. The valves must be all metal five years guarantee, and no adjustment necessary.
The radiator which is recessed in the wall has the advantage of being less visible, but unless you employ heat reflectors you will lose a lot of heat—and even with them you lose some. ”

“ To secure the boiler from accidents arising from the steam becoming too strong, a safety valve is used, similar to (p. 125) those described in Papin's steam engine, loaded with a weight equal to the strength which the steam is intended to have above the atmospheric pressure; for it is found expedient, even in condensing engines, to use the steam of a pressure somewhat above that of the atmosphere. ”

“ In supplying steam from the water compartment to the steam compartment, the inventor intends using a number of small perforations, not amounting in the aggregate to more than about one twentieth the size of the cylinder port, in connection with a number of small valves to be under control of the engineer, so that the amount of steam required can be readily regulated, yet carefully avoiding the possibility of all, when opened to their utmost capacity, forming as large an opening as the valve through which the cylinder is supplied. ”

“ If the trouble is in the valve or steam chest, you had best take it off and have the valve seat planed down, and the valve seated to it. This is the safest and best way. Never attempt to dress a valve down, you are most certain to make a bad job of it. ”

“ If there were no outside lap, steam would be admitted throughout the entire stroke and there would be no expansion. If there were no inside lap, exhaust would take place throughout the whole stroke, and the advantages of premature release and compression would be lost. Hence, outside lap affects the cut-off, and inside lap affects release and compression. A valve has lead when it begins to uncover the steam port before the end of the return stroke of the piston. ”

“ The journals of the shaft, and all cylindrical wearing surfaces, are finished by grinding in a manner that leaves them perfectly round. The crank-pin and cross-head pin are hardened before being ground. The joints of the valve-gear consist of pins turning in solid ferrules in the rod-ends, both hardened and ground. After years of constant use thus, no wear occasioning lost time in the valve-movements has been detected.
High speed and short strokes are essential elements of economy. It is now well understood that all the surfaces with which the steam comes in contact condense it. ”