THE DUPLEX PUMP

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N. Hawkins

Fig. 300.

THE DUPLEX STEAM PUMP.

Fig. 301.

The word duplex means two fold, or double, and has a wide application, as the duplex lathe, the duplex watch, etc., hence, the well-known duplex-pump is one in which two direct acting pumps are placed side by side and so connected that the steam piston of one operates the valve of the other. See Fig. 300.

Fig. 301 shows one of the smallest manufactured patterns of this type of pumps. Its dimensions are as follows: 2-inch diam. steam cylinder; 11/8-inch water cylinder; 22/3-inch stroke. Its capacity is .044 gallons per revolution; rev. per minute, 80; gallons per minute, 3.5. Steam pipe, 3/8-inch; exhaust pipe, 1/2-inch; suction pipe, 1-inch; discharge, 3/4-inch. Floor space occupied, 1´ 9 × 7 wide; requires 1/2 H.P.

The valve motion (see Figs. 302, 303) of one cylinder is communicated or produced by the piston of the other through the medium of rocker arms and links. By means of the small lost motion of the levers the pistons have a slight pause at the end of each stroke, which allows the water valves to seat quietly, thus preventing any slam or jar.

With this arrangement, as one of the steam valves must always be open, there can be no dead point, thus removing the liability of the pump to stick. The simplicity of the duplex movement is at once evident, each valve is dependent upon its counter part, and both directly control the action of the steam, which is supplied through one simple throttle valve.

Note.—Of the effect produced by the steam-moved direct-acting pump of much greater capacity it may be said there are now in use pumps of this class, exerting over 250 horse-power, delivering five million gallons of water in twenty-four hours through main pipes, say thirty inches diameter and fourteen miles long, without the use of an air chamber, and which do their work so quietly, steadily, and gently, that a nickel coin set on edge on the extreme end of the pump would not be overthrown by any jar or motion of the pump while it was doing this work.

Fig. 302.

Fig. 303.

The adoption of the Worthington design of duplex pumps, has been well nigh universal, especially so since the expiration of the earlier patents. Nearly all leading manufacturers now make “duplex pumps.” Single, compound and triple expansion.

Compounding consists of adding a second steam cylinder on the end of the high pressure in use, both using the same piston rod, the steam from the boiler being first used in the smaller cylinder, and at the end of the stroke of the piston being exhausted behind the piston of the larger cylinder on its return stroke. In this way the measure of the expansion of the steam used, was the relation of one cylinder to the other.

By this arrangement a much smaller steam cylinder, for using the high pressure steam, could be adapted to do the same work, for in addition to the pressure of steam working full stroke in the small cylinder, was to be added the pressure of the steam being expanded in the large cylinder.

In addition to this, for large compound and triple expansion engines was added the further economy realized by attaching a condenser to form a vacuum in the large steam cylinders.

Adapting these newer improvements in the marine engine coupled with what had previously been accomplished in the direct-acting steam pump, they were at once brought up in size, capacity, and economy alongside the previously constructed rotative pumping engines.

The history of the invention of this pump is given on pages 69 and 70; to these pages a careful attention is advised, as they briefly describe also the fundamental principles of its operation. This form of steam pump has been so long and generally in use that the valve mechanism is already familiar to most engineers.

The simplicity of both its theory and its practical application obviates the necessity of devoting very much space to its consideration. The final improvement made by Worthington in connection with the steam duplex pump was in the adaptation of triple expansion in its steam ends.

The illustrations, Figs. 302 and 303, are sectional views of one side, or half, of the Worthington steam pump, showing two different designs. They illustrate the interior arrangement of the pump. The valve, as may be seen at, E, is an ordinary slide valve; the motion of this valve is controlled by a vibrating arm, F, which swings through the whole length of the stroke. The moving parts are always in contact, which ensures smooth and even motion.

This valve motion is the prominent and distinguishing characteristic of the Worthington duplex pump. Two steam pumps are placed side by side and so combined that one piston acts to give steam to the other, after which it finishes its own stroke and waits for its valve to be acted upon by the other pump before it can renew its motion. This pause allows the water valves to seat quietly, and removes any harshness of motion. As one or the other of the steam valves is always open, there is no dead point, and therefore the pump is always ready to start when the steam is admitted.

Fig. 304.

In the plunger and ring pattern, Fig. 302, there is a double-acting plunger, B, working through a deep metallic ring bored to fit the plunger. The plunger is located some inches above the suction valves, leaving a settling chamber, into which any foreign substance may fall out of the way of the wearing surfaces. Both the plunger and ring can be taken out and either refitted or, when necessary, renewed. The valves consist of small discs of rubber, or other suitable material, and are easily accessible through convenient handholes. This pattern is recommended where the liquid to be pumped contains small quantities of grit or foreign material, or where there is an unusually long or high suction lift.

In the piston-pattern pump, Fig. 303, there is a packed water piston, G, working in a brass-lined cylinder, H. Both the suction and the discharge valves are located above the water pistons, so that the pistons may be at all times submerged. This pattern is recommended where the liquid to be pumped contains no grit or foreign material.

Fig. 304 shows the Worthington Admiralty pattern boiler feed pump which is designed to meet the requirements of the United States Bureau of Steam Engineering for steam boiler pressure up to 250 lbs. to the square inch. The ordinary slide valves are replaced by piston valves with outside, adjustable, lost-motion links, making it possible to readily adjust the stroke. The water end is made of composition, gun metal, or cast-iron, as desired. When made of cast iron the water end is brass-fitted throughout.

Table of Sizes, Capacities, Etc.

Diameter of
Steam
Cylinders		 Diameter of
Water
Pistons		 Length
of
Stroke		 Horse-power
of Boiler based
on 45 pounds of
water per hour,
which this
pump will
supply at
slow speed.
41/2 23/4 4 170
51/4 31/2 5 280
6 4 6 470
6 41/2 6 590
71/2 5 6 670
9 6 6 960
71/2 41/2 10 800
9 6 10 1400
10 7 10 2200
12 81/2 10 3200
12 91/4 10 3800
14 10 15 4800
Diameter of
Steam
Cylinders		 Diameter of
Water
Pistons		 Length
of
Stroke		 Sizes of Pipes for
Short Lengths
To be enlarged as
length increases.
Steam
Pipe		 Exhaust
Pipe		 Suction
Pipe		 Delivery
Pipe
41/2 23/4 4 3/4 11/4 2 2
51/4 31/2 5 1 11/2 21/2 21/2
6 4 6 11/2 2 4 3
6 41/2 6 11/2 2 4 3
71/2 5 6 11/2 2 5 4
9 6 6 2 21/2 5 4
71/2 41/2 10 11/2 2 4 3
9 6 10 2 21/2 5 4
10 7 10 2 21/2 6 5
12 81/2 10 21/2 3 6 5
12 91/4 10 21/2 3 6 6
14 10 15 21/2 3 8 6
Diameter of
Steam
Cylinders		 Diameter of
Water
Pistons		 Length
of
Stroke		 Approximate Space
Occupied
Inches
Height Depth Width
41/2 23/4 4 38 18 23
51/4 31/2 5 46 22 29
6 4 6 50 23 32
6 41/2 6 50 23 32
71/2 5 6 54 28 33
9 6 6 57 27 36
71/2 41/2 10 66 28 33
9 6 10 68 27 36
10 7 10 77 34 40
12 81/2 10 86 39 44
12 91/4 10 86 39 44
14 10 15 110 36 50

A notable feature in this pump is the location of the exhaust passage; this opening is underneath the cradle—or the part that the pump rests upon—just forward of the steam cylinders. The flanges of the steam end and cylinders and the steam chest cover have been made heavier than the regular and strengthened to withstand the higher pressures.

Fig. 305 is a sectional view of a larger size duplex pump than the one shown in Fig. 302. The plunger, B, packing is identical, but the number of water valves is double; access for cleaning the suction chamber, C, is had by removing the hand hold plate at the side and in the center. The discharge valves are reached through the hand hold at D.

Fig. 305.

The following rule applies to nearly all duplex pumps of the Worthington type. The valves are usually of the common “D” valve type, working on the cylinder iron, or bronze seats, and suitably “set.” Sufficient cushion at the end of each stroke is provided by separate valves in the ports.

Rule.—1, Locate the steam piston in the center of the cylinder, Fig. 305. This is accomplished by pushing the piston to one end of its stroke against the cylinder head and marking the rod with a scriber at the face of the stuffing-box, and then bringing the piston in contact with the opposite head; 2, divide exactly the length of this contact stroke. Shove the piston back to this half mark, which brings the piston directly in the center of the steam cylinder, F; 3, perform the same operation with the other side; 4, place the slide valves, which have no lap, to cover all the ports, E; 5, pass the valve stem through the stuffing-box and gland. The operation of placing the pistons in the center of their cylinders will bring the levers and rock shafts in a vertical position; 6, screw the valve stem through the nuts until the hole in the eye of the valve stem head comes in a line with the hole in the links, connecting the rocker shaft; then put the pins in their places; 7, adjust the nuts on both sides of the lugs of the valves to leave about 1/4 or 1/8 loss motion on each side.

This process of adjustment being performed with both cylinders, the steam valves are set. In short the travel of the two valves is simply equalized.

The pattern of pump shown in Fig. 306, is especially designed for use in connection with hydraulic lifts and cranes, cotton presses, testing machines, hydraulic riveting and punching machines, and hydraulic presses of all kinds. Also for oil pipe lines (see Table, page 341), mining purposes, and such services as require the delivery of liquids under heavy pressures.

There are four single acting outside packed plungers, which work into the ends of the water cylinders, the latter having central partitions; each individual valve has its own cover or bonnet. The arrangement of compound steam cylinders is shown. The water valves are easily accessible, and are contained in small chambers, capable of resisting very heavy pressures. The general arrangement shown in the engraving is subject to numerous alterations, according to various requirements, but the general characteristic of four outside packed plungers is in all cases preserved.

Fig. 306.

Table.

Steam
Cylinders.		 Water
Plungers.		 Stroke. Capacity in Gallons,
per Stroke
each Plunger.		 Strokes per
Minute,
each
Plunger.
Ins. Ins. Ins.
16 5 12 1.02 50 to 100
16 6 12 1.47 50 „ 100
16 7 10 1.66 50 „ 100
16 7 18 3.00 40 „ 80
16 8 12 2.61 50 „ 100
16 8 18 3.91 40 „ 80
16 9 12 3.30 50 „ 100
181/2 7 12 2.00 50 „ 100
181/2 71/2 12 2.30 50 „ 100
181/2 8 18 3.91 40 „ 80
181/2 9 18 4.95 40 „ 80
181/2 10 12 4.08 50 „ 100
181/2 10 18 6.12 40 „ 80
20 8 12 2.61 50 „ 100
20 8 18 3.91 40 „ 80
20 9 12 3.30 50 „ 100
20 9 18 4.95 40 „ 80
20 10 12 4.08 50 „ 100
20 10 18 6.12 40 „ 80
Steam
Cylinders.		 Water
Plungers.		 Stroke. Capacity of
Both
Cylinders, in
Gallons,
per Minute.		 Steam Pipe.
Ins. Ins. Ins. Ins.
16 5 12 102 to 204 21/2
16 6 12 147 „ 294 21/2
16 7 10 166 „ 332 21/2
16 7 18 240 „ 480 21/2
16 8 12 261 „ 522 21/2
16 8 18 312 „ 625 21/2
16 9 12 330 „ 660 21/2
181/2 7 12 200 „ 400 3
181/2 71/2 12 230 „ 460 3
181/2 8 18 312 „ 625 3
181/2 9 18 396 „ 702 3
181/2 10 12 408 „ 816 3
181/2 10 18 490 „ 980 3
20 8 12 261 „ 522 4
20 8 18 312 „ 625 4
20 9 12 330 „ 660 4
20 9 18 396 „ 792 4
20 10 12 408 „ 816 4
20 10 18 490 „ 980 4
Steam
Cylinders.		 Water
Plungers.		 Stroke. Exhaust Pipe. Suction Pipe.
Ins. Ins. Ins. Ins. Ins.
16 5 12 3 4
16 6 12 3 5
16 7 10 3 6
16 7 18 3 7
16 8 12 3 7
16 8 18 3 8
16 9 12 3 8
181/2 7 12 31/2 6
181/2 71/2 12 31/2 6
181/2 8 18 31/2 8
181/2 9 18 31/2 8
181/2 10 12 31/2 10
181/2 10 18 31/2 10
20 8 12 5 7
20 8 18 5 8
20 9 12 5 8
20 9 18 5 8
20 10 12 5 10
20 10 18 5 10
Steam
Cylinders.		 Water
Plungers.		 Stroke. Discharge Pipe. Water Press.
Pump End will
stand, in lbs., per
square inch.
Ins. Ins. Ins. Ins.
16 5 12 3 450
16 6 12 4 450
16 7 10 5 300
16 7 18 6 450
16 8 12 6 300
16 8 18 7 450
16 9 12 7 250
181/2 7 12 5 250
181/2 71/2 12 5 300
181/2 8 18 7 450
181/2 9 18 7 250
181/2 10 12 8 250
181/2 10 18 8 250
20 8 12 6 450
20 8 18 7 450
20 9 12 7 250
20 9 18 7 250
20 10 12 8 250
20 10 18 8 250

A test of the superiority of this method of moving, and controlling long columns of fluids under extreme heavy pressures was made at the time of the introduction of long pipe lines for conveying oil from the wells to the seaboard.

Note.—After trying various kinds of pumps for forcing the oil through these long pipes, and after having a succession of disasters in the way of burst pipes, and leaking joints, it was decided to test the efficiency of the direct-acting duplex steam pump. These pumps were placed in the various stations along the pipe lines, and after a continued service of many years, have shown their perfect adaptation to that exceptionally hard service. These pumps convey the oil over mountains where at times the coupled lines have been over one hundred miles long between the pumps, and where the pressure on the plunger of the pump sometimes rises to 1,500 lbs. per square inch.

J. F. Holloway.

Fig. 307.

COMPOUND DUPLEX PUMPS.
(With The Deane Switch Valve.)

The application of this valve is shown in Fig. 307, on the opposite page. It can be attached to any regular Compound or Triple Expansion Pump, and if not in use does not in any way impede the regular running of the machine.

The Deane switch valve is a device by which compound low service pumps may be converted into powerful fire pumps. This appliance consists of a valve of such construction that steam may be allowed to enter the cylinders as usual for compounding, or may be diverted by simply moving a lever, when all four cylinders receive steam at boiler pressure, each exhausting independently to the atmosphere. The change makes each steam cylinder available for its maximum power, all four cylinders develop their full power, and its effect can be utilized in powerful fire streams.

It should be borne in mind in justice to the manufacturers that the Deane switch valve is not to be classed with the ordinary two or four-valve arrangement, which, while admitting initial steam to the second cylinders, develops no power in the first, or, as it is sometimes arranged, uses initial steam in all four cylinders and develops less power than if the second cylinders were used independently.

This valve is recommended by the Insurance companies, and compound duplex pumps fitted with the Deane switch valve will be accepted in place of the Underwriter pump of similar capacity. This valve is also frequently used where two widely differing water pressures are required for other purposes than for fire protection.

Every machine is subject to rigorous tests before leaving the factory, including a 300-pound test of the water cylinders. Every pump is guaranteed to be in full accordance with the specifications.

UNDERWRITER FIRE PUMPS.

The Insurance Companies have issued detailed specifications for the construction of fire pumps to be known as Underwriter Fire Pumps. They have agreed that such pumps with their specified attachments be recognized as the approved type, and that pumps built and fitted up less perfectly be not approved in future installments.

The wide experience and systematic methods of the Insurance Companies place them in position to give valuable suggestions as a result of their observation and experiment, and these are embodied in carefully drawn regulations issued by their Engineering Department.

The specifications are very exacting in every particular, entering into the design, material, and workmanship in minute detail. They call for a number of fittings and attachments not usually furnished, and a most rigid test at the factory before shipping, and by the Inspecting Engineers of the Insurance Companies after the pump is installed, which secures for the purchaser the certainty of having a machine which beyond any reasonable doubt can be relied upon to do its full duty when emergency arises calling for its use.

There are a few quite important features not found in pumps of usual construction. The pumps are composition fitted throughout, the water cylinder bushings and plungers and linings to stuffing-boxes are of composition, the piston and valve rods, made unusually heavy, are of Tobin bronze. The mixture of the copper and tin composing the plungers and bushings varies for the two so as to prevent their cutting. Owing to the very high speed at which these pumps are liable to be run during a fire, all the working parts are made excessively strong, and the valve area and water passages are larger than usual. The interior of each Underwriter pump is treated with a rust-proof coating, and every precaution taken so that the pump will start instantly after an indefinite period of disuse.

Figs. 307 and 308 exhibit two somewhat varying but acceptable forms of the duplex steam pump.

Among the attachments included in an outfit for the underwriter pump may be mentioned: an elbow or tee for the suction connection with a large suction air chamber, a set of brass priming pipes with special gate and check valves for the same, an automatic water pressure relief valve fitted to a cone and overflow pipe, a steam gauge and a special water gauge with duplex spring, each of which in the Underwriter Pump is mounted on an ornamental plate rigidly attached to the machine.

Fig. 308.

Straightway hose valves for the proper number of streams are placed in the neck to a very large discharge chamber, and there is also a large discharge opening for connection to the system of hydrants and sprinklers.

A stroke pointer is attached which travels between graduations marked on the yoke, indicating the length of stroke which pump travels, a one-point sight feed cylinder lubricator, a capacity plate with enamelled face giving instructions for operating, etc., is attached to each machine.

                                                                                                                                                                                                                                                                                                           

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