PUMP PARTS.

Fig. 181.

Water Ends.There are properly speaking four kinds of water ends to steam and power pumps:

1, A solid plunger, with a stuffing box used for heavy pressings in hydraulic apparatus, or as shown inFig. 182, for larger plungers.

2, A piston packed with fibrous material within the cylinder.See Fig. 181. The letter P inFig. 182and the following cuts indicates the plunger.

3, A plunger packed with a metal ring around the outside, as illustrated inFig. 183.

4, Two plungers,Fig. 184, connected outside of the cylinder with a stuffing box in two cylinder heads, through which the plungers work. These are more fully explained and illustrated as they occur in many examples as they are referred to in the oncoming chapters of this work.

The construction of the water ends of single cylinder and duplex pumps is practically the same; any slight differences which may be found are confined to minor details, which in no way affect the general design or operation of the pump.

The steam or power endsof numerous and varied makes of pumps are also as shown in the following pages of this work; all pumps actuated by power—steam, electric, etc.—are possessed of these two distinguishing features—1, a steam or power end, and 2, the water end.

Note.—This statement has exception in the cases of large pumping engines having a fly wheel or supplemental cylinders attached to an accumulator, in which case the steam is worked expansively.

Fig. 182.

Fig. 183.

The steam end of the ordinary single steam pump, and also of the duplex pump, differs from the steam cylinder of the steam engine in that the former has four ports to each cylinder, i. e., two steam ports and two cushioning ports as shown hereafter in figures.

Under the division of the work allotted to the “Steam Pump” will be found all necessary further notice of the steam ends of Pumps.

Pump Valves.The valve apparatus is perhaps the most important part of any form of pump and its design has a material bearing upon its efficiency.

Fig. 184.

Fig. 185.

The valves shown inFig. 181are carried by two plates or decks, the suction valves being attached to the lower plate and the delivery valves to the upper one. The upper deck, and sometimes both decks, are removable. The valves are secured to the plates by means of bolts or long machine screws, which, in turn, are screwed into the bridge across the board in the plate, as shown in Figs.185and186or capped as in Fig. 187. The valves in all pumps except the large sizes, which may properly be classed with pumping engines, are ofthe flat rubber disc type, with a hole in the center to enable the valve to rise easily on the bolt, the latter serving as a guide.A conical springis employed to hold the valve firmly to its seat, the spring being held in position by the head of the bolt, or cap, as shown.

Certain improvements in pump-valves have been made which tend to increase the durability and to prevent the liability of sticking, which is not an uncommon occurrence after the valves have become badly worn. The improved forms of pump valves are shown in Figs.186and187.

Fig. 186.

Fig. 187.

When these valves leak through wear the disc may be reversed, using the upper side of the disc next to the valve seat. This can be done with ordinary valves also, provided the spring has not injured the upper surface of the disc. Valve seats are generally pressed into the plates, although instances may be found where they are screwed. When pressed in they may be withdrawn by substituting a bolt having longer screw threads than the regular bolt, and provided with a nut, as shown in Fig. 188. The bolt is slipped through a yoke and screwed into the bridge. By turning the nut the seat can generally be started without difficulty.

Fig. 188.

Fig. 189 represents the customarygland and stuffing-boxin which the gland is adjusted by the nuts C and D upon two studs. After the adjustment has been properly made lock-nuts are tightened which leaves the gland free yet preserves the alignment.

It has been proven by practice—after long and costly experiments—that a number of small valves instead of one large one are far the most durable;durabilitybeing the question. Corliss, Leavitt, Holly and other leading pump builders had occasion to find the truth of this statement early in their careers. The “slamming” of large valves under moderate speeds proved itself an almost insurmountable difficulty until the principle of keeping the valve area as low as possible within reasonable limits had been fully demonstrated.

Fig. 189.

To illustrate the advantage of having a number of comparatively small valves instead of one large one, suppose a pump to be fitted with four 31⁄2-inch delivery valves at each end, the valves covering ports 21⁄2inches in diameter. The area of each port is 4·9 square inches. In order to provide an equal area between the valve and the seat the valve must rise a distance equal to one-fourth the diameter of the port.

The combined area of the four ports is 19·6 square inches, which corresponds to the area of a circular opening 5 inches in diameter, one-fourth of which is 11⁄4inches. It will be understood that the smaller valves can seat much more quickly and with less jar than the larger one, hence a larger number of small valves is not only better because of the great reduction in slippage, but they are also more economical, being subjected to less wear and tear.

The lift of valvesfor moderate or low speed pumps is seen inFig. 190and those for higher speeds inFig. 191. These engravings clearly show the relative position of the suction and discharge valves during the movements of the piston.

Fig. 190.

Fig. 191.

Pump slipor slippage is a term used to denote the difference between the calculated and the actual discharge of a pump, and is generally expressed as a percentage of the calculated discharge. Thus, when the slippage is given as 15 per cent. it indicates that the loss due to slip amounts to 15per cent. of the calculated discharge. Slippage is due to two causes, the time required for the suction and discharge valves to seat.

When pumps run very fast the piston speed is so high that the water cannot enter the pump fast enough to completely fill the cylinder and consequently a partial cylinder full of water is delivered at each stroke.High speeds also increase slippage, due to theseating of the valves. Fig. 191 represents a sectional view of the water end of a pump, showing the position of the valves during a quick reversal in the direction of the arrows, which illustrates the position of the valves corresponding to high speed. The valves in a pump, like almost every other detail in the operation of machinery, do not act instantaneously, but require time to reach the seats.

When pumps run at high speed the piston will move a considerable distance, while the valves are descending to their seats, and water flows back into the pump cylinder until the valves are tightly closed. The valves will remain in the raised position shown in Fig. 191 until the piston stops at the end of the stroke, and under high speed the piston will reach the position on the return stroke indicated by the dotted lineLby the time the valves are closed. The cylinder will be filled up to this point with water from the delivery chamber so that no vacuum can be formed until after the piston reaches this position. The volume of water that can be drawn into the cylinder must necessarily be represented by the cubic inches cf space, minus the quantity which flows back during the time the valves are closing. It will thus be seen that the actual volume of water discharged is considerably less than a cylinderful, and the difference, whatever it may prove to be, is called, and is due to slippage.

Fig. 192.

Fig. 190represents the same pump running at a comparatively low speed. It will be noticed that the valves have not been raised as high as inFig. 191, because a longer time being allowed for the discharge of the water, a smaller orifice is sufficient. It will be seen also that the piston, moving at a lower velocity, cannot travel as far inFig. 190before the valvesseat, and consequently a vacuum can be created in the cylinder earlier in the stroke, and a larger volume of water can therefore be drawn in during the return stroke. In the latter case it is evident that the volume of water drawn into the cylinder will be nearly equal to a cylinderful and consequently the loss by slippage must be correspondingly less.

In order to reduce the loss by slippage several valves are used instead of a single valve of equal area. A flat disc valve will rise a distance equal to one-fourth the diameter of the port or of the opening in the seat to discharge the same volume of water that can flow through the port in the same time. In practice the rise exceeds this proportion of one-fourth a trifle, owing to the friction of the water, and this is especially true at high speeds.

Fig. 193.

Reinforced pump valves.Where pure gum has been used for pump valves it has always proved too soft and when it has been compounded with other substances it has been found too hard to withstand the severe duty to which it is subjected as a material for pump valves.

In the accompanying Fig. 192 is shown the Braden pump valve, which is made ofcomposition of rubber having wire rings embedded in the center of the disc. The composition has been removed from a section to show these rings. A ferrule ofcomposition metal forms a hub around the center through which the bolt or stud passes to guide the valve and to prevent excessive wear of the hole.

Its wire coil frame work clothed with rubber maintains a due amount of stiffness, with a degree of flexibility which prevents its bulging into the holes in the seats, or sticking therein, and thus impairing the suction and discharge. Both sides, the upper as well as the lower, are made available for service. These qualities of stiffness and flexibility combined, permit this valve to adjust itself to form a water-tight seat.

Figs. 194, 195, 198.

Figs. 196, 197.

Armored pump valves.As represented in Fig. 193 this is a valve made by stamping a metal disc out of steel which is then plated with copper to protect the surface and secure the adhesion of the rubber. Marginal notches are left on the inside and outside edges of the plate and rubber is moulded around these, and vulcanized to the required hardness; a brass or copper plate may be used instead of steel and the plates may be corrugated radially to increase their stiffness when the area of the valve is large.

Experience proves that the water valve adopted together with its location, has a material bearing upon the efficiencyof any pump; easy seating valves are subject to more or less slippage, owing to tardy seating; the location of water valves should be above the pump cylinder, inasmuch as in operation the pump is always primed, while if suction valves are placed below, any wear on the valves or valve seats, or obstruction under the valves, will cause the water to leak entirely out of the water cylinder, making it necessary to prime the pump before it can be started.

Note.—The screwed seat is shown in Fig. 194, Stud Fig. 195, Metal Valve Fig. 196, Spring Fig. 197, and all put together in Fig. 198.

Fig. 199.

Valve seats, bolts and springsshould be of the best composition or gun-metal; and valves of composition, or hard or soft rubber, to suit the duty such pump is required to perform. These valve seats are screwed into the valve plate, and valves may be changed from composition to rubber by merely removing bolt, and substituting one for the other without removing the seat. This is of great advantage where a pump is to be used for hot water after being used for cold water.

Fig. 200.

Fig. 201.

Air chambersare placed upon the top of a pump, see Figs.199and200, and contain air for the purpose of introducing anair cushionto counteract the solidity of the water, thus preventing shocks as the water flows through the valves; and also for the purpose of securing a steady discharge of water.

The water being under pressure in the discharge chamber, compresses the air in the air chamber during each stroke of the water piston and, when the piston stops momentarily at the end of the stroke, the air expands to a certain extent and tends to produce a gradual stopping of the flow of water, thus permitting the valvesto seat easily and without shock or jar.

The capacity of the air chambervaries in different makes of pumps from 2 to 31⁄2times the volume of the water cylinder in single cylinder pumps, and from 1 to 21⁄2times the volume of the water cylinder in the duplex type.The volume of the water cylinder is represented by the area of the water piston multiplied by the length of stroke.

For single-cylinder, boiler-feed pumps and those employed for elevator and similar service the volume of the air chamber should be 3 times the volume of the water cylinder, and for duplex pumps, not less than twice the volume of the water cylinder. High speed pumps, such as fire pumps, should be provided with air chambers containing from 5 to 6 times the volume of the water cylinder.

The diameter of the neck should not exceed one-third the diameter of the chamber. When the pumps work under pressure exceeding 85 or 90 pounds per square inch, it is frequently found that the air gradually disappears from the air chamber, the air passing off with the water by absorption. In this case air should be supplied to the air chamber unless the pump runs at very low speeds, say, from 10 to 20 strokes for the smaller sizes and from 3 to 5 strokes per minute for pumping engines. At higher speed and with no air in the air chamber the valvesare apt to seat heavily and cause more or less jar and noise, and the flow of water will not be uniform. The water level in the air chamber should be kept down to from one-fourth to one-third the height of the air chamber for smooth running at medium and high speeds.

Note.—In large pumping plants small air pumps are employed for keeping the air chambers properly charged. In smaller plants an ordinary bicycle pump and a piece of rubber tubing are used to good advantage.

Vacuum chambersare shown in Figs. 199, 200 and 201. These devices are attached to the suction pipe. When the column of water in the suction pipe of a pump is once set in motion, it is quite important, especially under high speeds, to keep the water in full motion, and when it is stopped, to stop it gradually and easily. This is accomplished by placing a vacuum chamber on the suction pipe, as shown in the figures.

The location of the vacuum chamber may be varied to suit the convenience of the engine room arrangements. Fig. 199 represents the vacuum chamber at the side of the pump, Fig. 200 shows it opposite the suction and Fig. 201 represents its position at the end of the pump.

Fig. 202.

Fig. 203.

Vacuum chambersare practically of two designs, as shown in Figs. 202 and 203. The one shown in Fig. 203 should be placed in such position as to receive the impact of the column of water in the suction pipe. In order to do this effectively it should be placed in the position shown in Figs. 199, 200 or 201. The chamber illustrated in Fig. 202 is placed in the suction pipe below, but close to the pump.

The action of the vacuum chamber is practically the reverse of that of the air chamber.The object of the vacuum chamber is to facilitate changing continuous into intermittent motion. The moving column of water compresses the air in the vacuum chamber at the ends of the stroke of the piston, and when the piston starts the air expands (thus creating a partial vacuumabove the water) and aids the piston in setting the column of water in motion again.

Thus the flow of water into the suction chamber of the pump is much more uniform during each stroke of the piston than without the vacuum chamber, and consequently the pump can be run at higher speeds without increasing the loss due to slippage and without “slamming” of the valves. Vacuum chambers should be slightly larger than the suction pipe and of considerable length rather than of large diameter and short. The size of the neck is substantially the same as in the air chamber.

Fig. 204.

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