PUMPS AND PUMPING ENGINES.
THE FACE F is often planed all over which is another bad feature in this form of pump. Cut 15 shows a modification of the same type of pump which is much used. The advantages of this form are a barrel or liner that is easily renewed and by making a ram form of bucket the air space is reduced, but the disadvantages before mentioned still remain.
In vertical pumping engines when this form of pump is used the disadvantages are very much greater as the valves and buckets are even more difficult of access end the practice of building up from the pump barrel ought to be severely tabooed as should any break occur in the pump barrel or adjacent parts the whole engine must be dismantled to effect repairs. This of course is a very costly piece of work and takes at least twice as much time as the original time of erection. The engine house is also littered with parts of the engine for an indefinite period and much to the annoyance of the attending engineers and every one else having occasion to go into the engine room.
The question of first cost does not enter here as the cost is often just as great as a good fly-wheel or rotative pumping engine with outside packed glands. A great many of this style of pumping engine actuates its own air pump in conjunction with a jet condenser,the injection water and products of condensation being returned to the well to be again in turn pumped into the city mains. – This is a most reprehensible practice and ought never to be allowed. The average water supplied to cities is bad enough without the addition of filthy grease; evidence of this is often seen on the sight glass of the air vessels, the glasses being coated with the grease. Condensers should in all cases be separately driven and should be surface condensing. With such condensers less steam is used and the to this and by the use of suitable separators most of the oil or grease can be eliminated and a hotter and purer water returned to the boilers.
In most instances a better vacuum can be obtained and the speed, and therefore the capacity of the air and circulating pumps can be exactly proportioned to the horse power or steam used by the pumping engine. Whee there are a number of engines it is not difficult to so arrange the exhaust pipes that any condenser can be cut out of use for repairs and clean, ing without having to lay off the entire pumping engine for such a purpose. The pipes can also be so arranged that the pumping engines could be worked high pressure or non-condensing in case of necessity; all these requirements are more than worthy of consideration by all city engineers as it is their duty to see that the long suffering public have the best and most efficient plant for their money.
A wise general always provides for retreat although he may feel confident of victory. An accident might happen that would give the victory to his adversary and if he had not or does not provide for retreat he loses his whole army. So with the pumping engine, every advantage known to the engineer should be taken advantage of and all arrangements made so that the pumping engine could, so to speak, fight to the last gasp in case of emergency.
Another important point that is often altogether lost sight of is the want of suitable lifting tackle of a permanent character in the engine house. Surely when three or four hundred thousand dollars are spent on a plant, it is a small matter indeed to spend three or four thousand dollars for a hand-power travelling crane that will range every part of the machinery.
Such a crane ought to be erected before the pumping plant is on the ground, as such a machine will save at least half of its cost in the erection of the machinery, and what it will save afterwards when repairs are to be made, is simply incalculable. It also keeps the engine room clear of unsightly, and often unsafe, sheer legs, with their attendant ropes litered around in everyone’s way. The want of such appliances often is the inotherwise be the case. As a part difficult to get at and requiring several men to handle heavy portions of the machinery, is often allowed to go too long and is only attended to when it will not stand being left any longer, and then the attendants are forced to make repairs.
Figure 15 shows another form of pump that is much used. ‘This form has the liner or working barrel inserted so that in case of excessive wear a new working barrel can be put with less trouble and at less cost than where the piston type is used; the elongated piston also fills up much space that would otherwise be filled with water. In cases where it is desirable to start up without charging, the pump would of course get rid of the air much more rapidly as the elongated piston fills up as much of this air space, but as no modern plant is without suitable charging valves this point is not of much advantage.
Other theories regarding this type is that the wearing surface is very largely increased, but against this wb have the extra weight on this surface ; in any case, suitable packing rings ought to be provided, so that as much leakage as possible is guarded against. The valves alone will do enough leaking without allowing the water other loopholes for escape.
The question of the best form of valve is a very difficult one to decide ; in fact, no one form of valve would suit all cases, and certainly would not suit all engineers, many believing implicitly in a certain form of valve, not because it is the best, or they think so, but because they have been brought up to think so, and because the boss says it is the best, and they (the men) do not take the trouble to think for themselves. Experiments are costly. Men willing to spend money this way find out more in a month than they would in years by going on in the old way, in many cases using a certain form of valve because it is cheap.
In the course of my experience I have used I think nearly every form of valve, soft or pliable rubber, hard rubber, bronze, steel and other materials. Some people want double beat valves, some pyramid valves, some clack or flap valves and some the plain mushroom valve. There is very much to be said for the old time plain mushroom valve, but when we get up to large sizes we either have to put in a number of such valves or adopt some other method or form of valve, although tory results at slow speed, but they are liable to do a good deal of kicking if the beats exceed twelve or fourteen per minute. On the other hand 1 have seen the same form of valve 5 inch and 6 inch diameter working under pressures from 700 to 10,000 lbs. per square inch (which gives a total pressure vastly greater than any that was on the 18 inch valve) working at 35 to 40 beats per minute and one could hardly hear them beat. A limit of 12 inch diameter seems to be about what a mushroom valve ought to be, then as the diameter of the rams increase put in group of valves.
The double beat or equilibrium valve is theoretically the best valve, but the mechanical difficulties are rather against it, as it takes a first-class mechanic to make it seat evenly on both seats and when that is done the difficulty of balancing comes in as it is practically impossible to cast it of even thickness all over. This is a little matter that is often lost sight of and the valve causes much trouble because it will not wear evenly, one seat wearing more than another, and one side faster than the other. The rough-and-ready careless man will then throw it out and say it is no good anyway instead of trying to get at the cause of the unequal wear and rectifying it.
This form of valve is of course expensive and finds little favor with the cheap and nasty builder who wants something that can be run by a boy who gets a salary of perhaps $5 per week, and consequently turns out work that is fearfully and wonderfully made, and seats where it touches, being usually in two spots, as the valve is sure to Ire oval, the face angle also differing in every valve.
t his sort of work would not of course be tolerated by any high-class firm knowingly, but valves are as a rule not looked to with sufficient care, many foremen and superintendents thinking them so simple that any one can turn them. Such, however, is not the case, and this part of the pumping engine is really of more importance than the steam end as much more unknown toss can take place here, while at the steam end there are many warnings that something is Wrong if all is not as it should be. The best of men and lathes should be used for this important part of the pumping engine, the better the work is from the lathe the less time need be spent scraping an 1 seating, and it t akes a good m an to do this scraping and s > ating in a proper manner. A small leak in a valve mighty soon becomes a large one, especially where there is any grit in the water, so that tile valve work cannot be made too good, and facilities for reaching the valves must be of the best and easiest kind. This unfortunately in the style of pump last illustrated, is often if not always neglected. A mean little manhole being all that is as a rule provided and in the vertical style of pump it is worse still.
While we see very often every refinement known to modern science taken advantage of at the steam end of a pumping engine, we see at the water end work and arrangement of parts that would have been ridiculed even in Watt’s time; the price paid for the plant is not always to blame by any means as often as not, a good price is paid for work that is anything but good either in workmanship or design, before leaving the subject of valves 1 would strongly advise that the practice of putting as many small valves as can be conveniently crowded into a pump be guarded against. It is simply against reason to suppose that so much extra surface will stand as good as when there is only about half the surface. As an example take a pump that requires 16 4-inch valves the circumference being 12.56 inches, this x 16—200.96 inches, whereas if 4 8 inch, valves were used the added circumference is only 100.52 inch, or just half what the same area in 4-inch valves means. Not only this, we get more out of the four 8-inch valves because the room taken up by the wings or bosses is more in proportion to area in the 4-inch valves than what it is in the 8-inch valves.
This large increase in linear inches to keep tight where small valves are used, seems either to be ignored or simply never has been calculated by those who use such an arrangement. The newest beginner in the study of the science of engineering can comprehend at once that it is more difficult to keep 200 inches water-tight than it is to keep 100 inches watertight,but in spite of this very obvious fact, the practice still goes on, and probably will do so until the buyers of pumping engines learn a little more engineering wisdom and get to know more about the detail of the various parts, instead of looking at a pretty cut and reading over a beautifully carried-out list of duty trials, showing how little steam the said pumps uses, tut invariably leaving out all mention of any weir as being used at the water end ; this part, of course, being of secondary importance, and measuring will do for that, along with the number of strokes counted by a machine that can easily go wrong or be tampered with. Never mind the duty trials ; they are pretty, certainly, but the coal pile at one end and the gallons of water at the other end is what ought to be looked at. and not for a few hours, but regularly kept every day by a reponsibie man detailed off for that special duty.