THE STEAM END.
a.These must be of hard close iron with metal so distributed as to ensure sound castings and freedom of shrink cracks. The following are the minimum thicknesses acceptable:
14″Diam.7⁄8″thick16″„15⁄16″„18″„1″„20″„11⁄8″„
b.The inside face of the steam cylinder heads and the two faces of the piston must be smooth surfaces, fair and true so that if the piston should hit the heads it will strike uniformly all around, thus reducing to a minimum the chances of cramping the piston rod or injuring the pump.
c.All flanged joints for steam must be fair and true and must be steam tight under 80 lbs. pressure if only a packing of oiled paper1⁄100inch thick covered with graphite were used. Jenkins, “Rainbow” or equivalent packing of not exceeding1⁄32inch original thickness is acceptable. Oiled paper is not acceptable as a final packing, as it burns out.
For size of steam and exhaust pipes, standard flanges and bolting,see Art. 39.
The specifications originally required machine facing for all these surfaces. The art of machine molding from metal patterns with draw plates, etc., has, however, attained such excellence in certain shops, that in regular practice “foundry faced” cylinder heads and piston faces can be made true and fair, and steam joints can be made, tight under 80 lbs. pressure with a packing of oiled paper only1⁄100inch thick.Under proper assurance that this precision can be obtained in regular practice at the shop in question, foundry finish may be accepted on cylinder heads and piston faces, steam chests and steam-chest covers.In the case ofbuilt-up pistons, of separable form, it must be conclusively shown that the boring and finishing are carried on by such methods as will ensure the faces of pistons being exactly square to the piston rod and exactly parallel to the cylinder head.In the case ofsolid pistonsthe two faces must be machine faced, as proper parallelism cannot well be obtained by foundry methods.Ordinary foundry finish secured by the old methods and wooden patterns is not acceptable and acceptance of any foundry-finish can only be secured after a special investigation of shop practices.
The specifications originally required machine facing for all these surfaces. The art of machine molding from metal patterns with draw plates, etc., has, however, attained such excellence in certain shops, that in regular practice “foundry faced” cylinder heads and piston faces can be made true and fair, and steam joints can be made, tight under 80 lbs. pressure with a packing of oiled paper only1⁄100inch thick.
Under proper assurance that this precision can be obtained in regular practice at the shop in question, foundry finish may be accepted on cylinder heads and piston faces, steam chests and steam-chest covers.
In the case ofbuilt-up pistons, of separable form, it must be conclusively shown that the boring and finishing are carried on by such methods as will ensure the faces of pistons being exactly square to the piston rod and exactly parallel to the cylinder head.
In the case ofsolid pistonsthe two faces must be machine faced, as proper parallelism cannot well be obtained by foundry methods.
Ordinary foundry finish secured by the old methods and wooden patterns is not acceptable and acceptance of any foundry-finish can only be secured after a special investigation of shop practices.
d.Heads at both ends of cylinder must be beveled off very slightly over a ring about one inch wide, or equivalent means provided to give steam a quick push at piston, should it stand at contact stroke.
a.The stress on bolts or studs in connection with steam cylinders must not exceed 7,500 lbs. per square inch under a test pressure of 80 lbs. steam, disregarding such initial strain as may be due to setting up. (Compute pressure area out to center line of bolts.)
No stud or bolt smaller than3⁄4inch should be used to assemble parts subject to the strain of steam pressure as smaller bolts are likely to be twisted off.
a.The steam cylinders and water cylinders must be connected by such a form of yoke as requires no packing, a metal to metal joint at this connection being considered necessary. The piston-rod stuffing box heads should concentrically fit the counter-bore of the yoke.
If packing is put into these joints, there is a chance of the steam and water ends getting out of alignment and leaking at the joint between cylinders and yoke.
If packing is put into these joints, there is a chance of the steam and water ends getting out of alignment and leaking at the joint between cylinders and yoke.
a.The area of each exhaust steam passage, at its smallest section, must not be less than 4 per cent. of the area of the piston from which it leads.
This is a large increase over the size heretofore common, but indicator cards which we have taken from pumps of several different makes indicate this to be one of the points in which improvement is most needed to accommodate the high speeds at which fire pumps are always supposed to run, and this unrestricted exhaust aids very materially in giving steadiness to the jet of water.
This is a large increase over the size heretofore common, but indicator cards which we have taken from pumps of several different makes indicate this to be one of the points in which improvement is most needed to accommodate the high speeds at which fire pumps are always supposed to run, and this unrestricted exhaust aids very materially in giving steadiness to the jet of water.
b.Each admission port must be not less than 21⁄2per cent. of area of its piston, and to avoid wasteful excess of clearance, these passages should not be bored out larger in interior of casting than at ends or passage.
c.The edges of the steam-valve ports must be accurately milled, or chipped and exactly filed to templets, true to line, and the valve seat must be accurately fitted to a plane surface, all in a most thorough and workmanlike manner and equal to high-grade steam-engine work.
d.To guard against a piston ring catching in the large exhaust ports, these ports must have a center rib cast with cylinder at cylinder wall.See also Art. 13d.
a.Clearance (including nut-recess, counter-bore, and valve passages) must not exceed 5 per cent. for contact stroke or about 8 per cent. for nominal stroke (i.e., contact stroke should overrun nominal stroke not more than one-half inch or not less than one-fourth inch, at each end).
b.The clearance space between face of piston and cylinder head must be reduced to smallest possible amount, and these contacting surfaces be flat, without projections or recesses other than the piston rod nut and its recess.
Some makers, with the idea that a fire pump need not be economical, have not taken pains to keep these waste spaces small.Securing small clearance costs almost nothing but care in design, and is often of value, since at many factories boiler capacity is scant for the large quantity of steam taken by a fire pump of proper size.
Some makers, with the idea that a fire pump need not be economical, have not taken pains to keep these waste spaces small.
Securing small clearance costs almost nothing but care in design, and is often of value, since at many factories boiler capacity is scant for the large quantity of steam taken by a fire pump of proper size.
a.May be either built up or solid, as maker thinks best.
It is believed that “solid” (cored) pistons with rings “sprung in,” are for fire-pumps much preferable to built-up pistons, since follower boltsdosometimes get loose.
It is believed that “solid” (cored) pistons with rings “sprung in,” are for fire-pumps much preferable to built-up pistons, since follower boltsdosometimes get loose.
b.Piston must not be less than four inches thick between faces. If solid, walls should be not less than1⁄2inch thick, and special care should be given to shop inspection to determine uniformity of thickness.
c.If built up pistons are used, involving follower bolts, such bolts must be of best machinery steel, with screw thread cut for about twice the diameter of the bolt and fitting tightly its whole length.
d.The width of each piston ring must exceed the length of the large exhaust port by at least1⁄4inch.
This is to avoid the possibility of piston ring catching in the port.
This is to avoid the possibility of piston ring catching in the port.
See also Art. 11d.
a.Slide valves must be machine fitted on all four of the outer edges, the exhaust port edges, and the surfaces in contact with rod connections.
b.The slide valve itself must have its steam and exhaust edges fitted up “line and line” with their respective steam and exhaust ports.
The adding of lap to these edges in lieu of lost motion is not acceptable further than a possible1⁄32of an inch to cover inaccuracies of edges.
The adding of lap to these edges in lieu of lost motion is not acceptable further than a possible1⁄32of an inch to cover inaccuracies of edges.
c.The valves must be guided laterally by guide strips cast in steam chest, and these strips must be machine fitted. The lateral play at these surfaces should not exceed1⁄16inch. The height of these guide strips should not be less than1⁄2inch, measuring from valve seat.
The construction must be such as to absolutely preclude the possibility of the valve riding up on top of this guide strip.
d.The valves must be guided vertically by the valve-rod itself, the inside end of which must be kept in alignment by the usual form of tail-rod guide.
The vertical play at these parts should not exceed1⁄8of an inch.
e.The surface of valves must be machine faced and accurately fitted to a plane surface, and be steam tight when in contact with the seat of steam valve.
a.The lost motion at the valves and the setting of them must be determined by a solid hub on the rod, finished in the pump shop to standard dimensions, so that no adjustment is possible after the pump is once set up.
This hub may be forged on the rod and then lathe-finished to standard dimensions, or it may be made by turning down a rod of the size of the hub. It is believed that Tobin bronze can be safely forged after a little experience, if care is taken to maintain the proper heat.
This hub may be forged on the rod and then lathe-finished to standard dimensions, or it may be made by turning down a rod of the size of the hub. It is believed that Tobin bronze can be safely forged after a little experience, if care is taken to maintain the proper heat.
It is recognized that the practice of making adjustable valve tappets located outside of the steam chest is a good thing in a large pump in constant service and operated by a skilled engineer, but for the infrequently used ordinary fire-pump, the utmost simplicity is desirable, and it is best not to tempt the ordinary man to readjust the valve gear.The common form of lost motion adjustment consisting of nut and check nut at each end of the slide valve is not acceptable, as these nuts are liable to become loose and may be incorrectly reset by incompetent persons. A long rectangular nut in the center of the valve is also not acceptable, as it can be moved out of adjustment. A solid hub made as a part of the rod is required, as it absolutely avoids the possibility of the hub becoming loose, an accident possible with a separate hub attached to the rod.The amount of lost motion should generally be such that admission takes place at about5⁄8of the stroke of the piston,i.e., for 12-inch stroke R. H. valve will be about to open when L. H. piston has moved 71⁄2inches to 8 inches from the beginning of stroke. When piston is at end of stroke the ports should be full open.
It is recognized that the practice of making adjustable valve tappets located outside of the steam chest is a good thing in a large pump in constant service and operated by a skilled engineer, but for the infrequently used ordinary fire-pump, the utmost simplicity is desirable, and it is best not to tempt the ordinary man to readjust the valve gear.
The common form of lost motion adjustment consisting of nut and check nut at each end of the slide valve is not acceptable, as these nuts are liable to become loose and may be incorrectly reset by incompetent persons. A long rectangular nut in the center of the valve is also not acceptable, as it can be moved out of adjustment. A solid hub made as a part of the rod is required, as it absolutely avoids the possibility of the hub becoming loose, an accident possible with a separate hub attached to the rod.
The amount of lost motion should generally be such that admission takes place at about5⁄8of the stroke of the piston,i.e., for 12-inch stroke R. H. valve will be about to open when L. H. piston has moved 71⁄2inches to 8 inches from the beginning of stroke. When piston is at end of stroke the ports should be full open.
a.Rock shafts must be either forged iron, forged steel, or cold rolled steel. Cast iron is not acceptable. The following are the minimum diameters acceptable:
500 gallon pump11⁄2in.750 gallon pump13⁄4in.1000 gallon pump2 in.1500 gallon pump2 to 21⁄4in.
b.The rock shaft bearings must be bushed with bronze and the bushings pinned firmly in place. The length of each of these non-corrosive bearings must be not less than 4 inches.
c.Rock shaft cranks, valve rod heads, valve rod links, and piston rod spools or crossheads may be wrought iron or steel forgings, or steel castings. If of a heavy, strong pattern, these parts, with the exception of valve rod links, may be of semi-steel or cast iron.
d.The sectional area of all connections between rock shaft cranks and valve rod must be such as to give a tensile or compressive strength substantially equal to that of the valve rod.
a.The valve motion levers must be steel, wrought iron, or steel castings. Cast iron is not acceptable. Steel castings, if used, must be deeply stamped with the name of the makers, with letters one-eighth inch high, near the upper end of each lever, where it can easily be seen,—thus “.....Steel Castings.”
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.
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.
b.The levers must have a double or bifurcated end at crosshead.
The double end is less likely than a single end to put an undue strain on the lever as the rod turns, and is also likely to give trouble from lack of lubrication or from a loosening of any small parts, and has proved to be the most satisfactory arrangement.
The double end is less likely than a single end to put an undue strain on the lever as the rod turns, and is also likely to give trouble from lack of lubrication or from a loosening of any small parts, and has proved to be the most satisfactory arrangement.
a.The valve motion stand must be securely dowel-pinned to the yoke castings, to prevent any movement after being once adjusted.
a.Cushion-release valves regulating the amount of cushion steam retained at ends of stroke must be provided.
b.The cushion release must be through an independent port as shown inFigs. 2and3, so located as to positively retain a certain amount of cushion steam.
The old form of cushion release through bridge between ports is not acceptable. This form while leading into the exhaust passage as formerly, differs by starting from a small independent port (about1⁄2-inch wide × 21⁄2inches long) through the cylinder wall, located about3⁄8or1⁄2inch back from the cylinder head. (The exact position for affording the best action has to be determined by experiment with each different make of pump, as it depends somewhat on the extent of clearance space and on thepoint of closure of exhaust by piston and somewhat on the weight of reciprocating parts.)Fig. 2.Fig. 3.This style of cushion port makes the pump safer in case cushion valves are unskillfully left open too wide and tends to prevent a pump from pounding itself to pieces in case of a sudden release of load, as by a break in suction or delivery mains, or by a temporary admission of air to suction pipe.Fig. 4.Pumps made with this form of cushion release, have given very satisfactory results, and if the ports are properly located, there will be no re-bound of piston.
The old form of cushion release through bridge between ports is not acceptable. This form while leading into the exhaust passage as formerly, differs by starting from a small independent port (about1⁄2-inch wide × 21⁄2inches long) through the cylinder wall, located about3⁄8or1⁄2inch back from the cylinder head. (The exact position for affording the best action has to be determined by experiment with each different make of pump, as it depends somewhat on the extent of clearance space and on thepoint of closure of exhaust by piston and somewhat on the weight of reciprocating parts.)
Fig. 2.
Fig. 2.
Fig. 3.
Fig. 3.
This style of cushion port makes the pump safer in case cushion valves are unskillfully left open too wide and tends to prevent a pump from pounding itself to pieces in case of a sudden release of load, as by a break in suction or delivery mains, or by a temporary admission of air to suction pipe.
Fig. 4.
Fig. 4.
Pumps made with this form of cushion release, have given very satisfactory results, and if the ports are properly located, there will be no re-bound of piston.
c.Cushion valves must be always provided with hand-wheels marked as per sketch, for the reason that very few men in charge of fire-pumps are found to clearly understand or to remember their use.
The lettering must be very open, clear and distinct, not liable to be obscured by grease and dirt, and of a permanent character.
It is desirable that spindle or wheel be so formed that a monkey wrench can get a grip to open a jammed valve.Fig. 5shows the stem flattened for this purpose.
It is desirable that spindle or wheel be so formed that a monkey wrench can get a grip to open a jammed valve.Fig. 5shows the stem flattened for this purpose.
Fig. 5.
Fig. 5.
d.The valve and stem of cushion valve must be in one piece without any swivel joint.
Swivel joints are apt to come apart and make it impossible to operate the valve.
Swivel joints are apt to come apart and make it impossible to operate the valve.
a.Piston rods for their entire length must be of solid Tobin Bronze, and the distinguishing brand of the manufacturers of this metal must be visible on at least one end of each rod.
b.The sizes must be not less than in table below.
Size of Pump.500 gal.750 gal.1,000 gal.1,500 gal.Diameter of rod2 inch.21⁄4inch.23⁄8inch.21⁄2inch.
c.The size and form of connection of rod to piston plunger and cross-head must be such that the stress in pounds per square inch at bottom of screw thread, or at such other point of reduced area as receives the highest tensile strain, shall not exceed 8,000 lbs. per square inch, when the steam pressure acting on the piston is 80 lbs. per square inch.
d.Piston rod nuts, in both steam and water ends, must be tightly fitted, and preferably of a finer thread than the United States Standard. This is to avoid as much as possible the unnecessary weakening of the rod at the bottom of the thread, and to reduce the tendency of the nut to work loose.
In practice 8 threads per inch has been found to give good satisfaction.
In practice 8 threads per inch has been found to give good satisfaction.
e.In addition to a tightly fitting nut, some reliable device must be provided, in both steam and water ends, for absolutely preventing these nuts from working off.
Fig. 6.
Fig. 6.
Fig. 6shows one form of such a locking device and illustrates the kind of security desired.
Fig. 6shows one form of such a locking device and illustrates the kind of security desired.
This device combines the advantage of a taper key and a split pin, and the elongated key-slot gives sufficient leeway to always insure that the key can be driven up tight against the nut and thus prevent it from even starting to work off. Other methods will be approved in writing, if found satisfactory.
This device combines the advantage of a taper key and a split pin, and the elongated key-slot gives sufficient leeway to always insure that the key can be driven up tight against the nut and thus prevent it from even starting to work off. Other methods will be approved in writing, if found satisfactory.
a.Valve Rods for their entire length must be of solid Tobin Bronze, with sizes not less than in table below.
Size of Pump.500 gal.750 gal.1,000 gal.1,500 gal.Diameter of rod1 inch.11⁄8inch.11⁄8inch.11⁄4inch.
b.The net area of valve-rod at its smallest section subject to tensile stress, must not be smaller than at bottom of U. S. standard screw thread on rod of diameter given above.
The construction of this rod as affecting lost motion at slide valve is specified under Article 15.
The construction of this rod as affecting lost motion at slide valve is specified under Article 15.
Fig. 7.
Fig. 7.
a.All six stuffing boxes must be bushed at the bottom with a brass ring with suitable neck and flange, and the follower or gland must be either of solid brass, or be lined with a brass shell3⁄16-inch thick, having a flange next the packing, as shown in the sketch.
The bottom of stuffing boxes and the end of glands should taper slightly towards the center as per sketch.
b.These glands should be strong enough to withstand considerable abuse, so as not to break from the unfair treatment of unskilled men.
a.A pressure gauge of the Lane double tube spring pattern with 5 inch case must be provided and attached to the steam chest inside the throttle valve.
The dial of gauge should be scaled to indicate pressures up to 120 lbs. and be marked “STEAM.”
This kind of gauge is used on locomotives and is the best for withstanding the vibration which causes fire-pump gauges to be often unreliable. Moreover, this double spring is safer against freezing.
This kind of gauge is used on locomotives and is the best for withstanding the vibration which causes fire-pump gauges to be often unreliable. Moreover, this double spring is safer against freezing.
a.Four brass drain cocks, each with lever handle and of one-half inch bore, are to be provided, and located one on each end of each steam cylinder.
Care should be taken to select a pattern of cock whose passageway is the full equivalent of a1⁄2-inch hole. Some patterns of1⁄2-inch commercial cocks although threaded for1⁄2-inch pipe thread have but a1⁄4-inch hole through them. Such are not acceptable.
Care should be taken to select a pattern of cock whose passageway is the full equivalent of a1⁄2-inch hole. Some patterns of1⁄2-inch commercial cocks although threaded for1⁄2-inch pipe thread have but a1⁄4-inch hole through them. Such are not acceptable.
a.A one-pint hand oil pump, to be connected below the throttle, and a one-pint sight feed lubricator, to be connected above the throttle, must be furnished with each pump.
b.Oiling holes must be provided for all valve motion pins, and for each end of both rock shafts.
a.A length-of-stroke-index must be provided for each side of pump. These must be of simple form for at all times rendering obvious the exact length of stroke which each piston is making, and thus calling attention to improper adjustments of cushion valves or stuffing boxes.
b.The gauge piece over which the index slides must have deep, conspicuous marks at ends of nominal stroke, and also light marks at extreme positions; it need contain no other graduations.
c.This stroke index must be rigidly secured to cross-head in such a way that it cannot get loose or out of adjustment.