TEST OF LOWELL PUMPING ENGINE
The report of the Lowell (Mass.) water board, recently come to hand, contains, along with other valuable information, all the data gathered by Consulting Engineer Charles A. Hague, of New York, acting for the city of Lowell in testing the new 8,000,000-gal. Holly pumping engine installed during the year reported. All this valuable information is concisely set forth in Engineer Hague’s report, which is as follows;
REQUIREMENTS OK TI1K CONTRACT.
The essential requirements of the contract are that the pumping engine is to be capable of pumping and delivering 8,000,000 United States gallons of water in twenty-four hours against a total hydraulic head of 62 ft.; with a steam pressure at the throttle valve of 120 lb. per square inch; and while pumping this quantity of water to show an economic duty equal to the raising of 120,000,000 lb. of water 1 ft. high, for each 1,000 lb. of dry steam used by the pumping engine and its appurtenances.
During the said test, the steam consumed by the engine was taken as the weight of condensed steam in the form of water delivered by the condenser air-pump, plus any amount observed as leakage and loss before reaching the weighing barrel, and minus 1 per cent, allowed for the entrainment of water in the steam as the contract calls for dry steam for the engine. The net amount so found was taken as the weight of dry saturated steam consumed by the engine, it having been understood that all steam used for jacketing, reheating and other uses about the engine itself, would be included in this net amount found.
The work done by the pumping engine against which the above mentioned amount of steam was charged, was taken as the weight of the quantity of water displaced by the plungers, multiplied by the head in feet represented by the total load observed and averaged during the test run.
I he results of the official test show that this pumping engine is capable of pumping 8,000,000 United States gallons of water per twenty-four hours against the prescribed load with a steam pressure of 120 lb. at the throttle valve: although owing to local conditions the duty tost was run at a rate of pumpage of approximately 0,500,000 gal. of water per twenty four hours. This rate of pumpage below full design capacity is sometimes claimed as a detriment to the engine and rendering it incapable of exhibiting its full capabilities as to duty accomplishment: but considering the high rate of rotative speed called for at full capacity, and the fairly high speed at which the test was actually run, and also considering that the high duty record is held by engines by much lower races of revolution than this test, in mv opinion there would be but little difference to the good so far as concerns economic duty it; operating this engine at the full capacity. In any case, however, the contractor has no grounds for complaint, for the reason that the engine developed a duty of more than 130,000. non ft. lb. per 1,000 lb. of dry steam at the capacity of fi,479,611 United States gallons, on plunger displacement: which if discounted say 5 per cent, for any possible losses in the way of slippage, the economic duty would still be 12.1,500,000 ft. lb. on a pumpage rate of 6.155,611 United States gallons net, per twenty-four hours. I* may be noted in passing that with water so clean and clear as Lowell has in its wells, an allowance of 5 per cent, is very liberal for slippage and losses through the pump valves, especially when the low head is taken into account. This test demonstrates then that the engine is capable of fully meeting the contract requirements.
Therefore, so fas as the above facts are concerned you will be justified in accepting the said pumping engine, provided that all outside and incidental claims against the con tractor be settled: also provided that the contract bond be held for one year at least after date of the formal acceptance of the machinery and its appurtenances, to hold the city of Lowell safe against faulty design and workmanship or defective materials employed in the construction of the said pumping engine and its appurtenances; all as provided for in the contract and specifications under which the pumping was constructed and installed in the Lowell waterworks.
DETAILS OF THE OFFICIAL TEST.
As the contract requirements for duty were based upon the quantity of steam used by the engine, the accurate determination of the steam used during the test was carefully gone into. The weight of steam used was taken as the discharge from the air pump plus the discharge from the steam jackets and receivers, the total amount discounted 1 per cent, for entrained water in the steam delivered at the main throttle valve. The discharge of the air pump from the surface condenser, and also the discharge of the steam traps from the jackets and receivers, were delivered into a hot well and from this hot well lifted by the feed pump attached to the main engine, into a receiving barrel. From the receiving barrel the water was run into a weighing barrel placed upon a platform scale; the empty barrel was balanced at 107.5 lb. and ‘a full barrel was balanced at 407.5 lb. thus making 300 lb. net of condensed steam at each filling of the weighing barrel. The number of charges of 300 lb. was tallied throughout the test and a portion of the barrel added at the finish to complete the exact even time reqtiircd by the run; to the amount so found there was added the weight of drainage found to be delivered from the second receiver, this amount from the second receiver being ascertaind by catching the discharge m a bucket and weighing it, a sufficient number of times to establish a rate per minute. Finally the steam consumption was corrected by deducting the entrained water within the initial steam as according to the contract the engine was entitled to dry steam in computing its duty performance.
As the determinations of steam consumption were made from discharges from the condenser, no account was taken of losses from boilers, steam and feed pipes, calorimeter, drainage before the steam reached the throttle valve, etc.
NET STEAM USED BY THE ENGINE.
‘File net, dry saturated steam, used by the engine during the test prescribed by the contract was ascertained by adding the known weight of water drawn from the receiving barrel into the weighing barrel, to the weight of water discharged by the drip of the second receiver, as that drip was the only observable discharge aside from the air pump and steam jacket deliveries. The sum so found was discounted by the entrainment of 1 per cent, as the ascertained amount of water contained by the steam passing the engine throttle valve. The results were as follows:
Thirty-five barrels, each containing 300 lb.. 10,500 lb.
Portion of the thirty-sixth barrel. 178.5 lb.
Drip from second receiver, 2.11 lb.
Total. 10,909.5 lb.
Less i per cent, water entrained. 109.09 lb.
Net steam used by the engine, 10,800.41 lb.
THE PU NI ER LOAD FOR DUTY CALCULATIONS.
The plunger load being one of the most vital factors in the duty calculations, great care was taken to read it correctly, and to this end a regular water pressure gauge, two mercury columns, a water gauge glass and a measured vertical distance were utilized. A bench mark was established at the under side of the top nut of the glass water gauge on the receiving lank in the basement, and to this bench mark all vertical measurements were referred. The level of the water in the receiving tank from the tubular wells was read from a calibrated scale set against the glass gauge of the receiving tank in such a manner that the readings were downward from the established bench mark referred to.
The difference in elevation was noted between the bench mark and the water pressure gauge on the engine, and also between the centre of the pressure gauge on the engine and a datum mark for the pressure mercury column, and regular readings were taken during the test between this datum mark and the actual elevation of the mercury in the short leg of the apparatus,
A suction mercurv column was attached to the upper part of the receiving tank and the readings reduced to feet were averaged anil taken as the suction lift at this point.
Thermometers were hung as nearly as could be to each of the mercury columns and their readings used for the correction of the mercury readings on account of temperature, the value of the mercury to indicate pressure being taken as .88488 of an inch in height with mercury at 55° F. to balance a water colum 1 ft. in height at 48° F., these values being derived from the United States Meteorological tables and considered correct by good authorities. The average temperature at the pressure mercury columns was 98° F. and the suction mercury column 68° F.
The readings were taken every twenty minutes and the plunger load with all corrections was as follows; the determinations for pressure being made both by mercury column and by the regular pressure gauge and averaged:
By the Pressure Gauge.
Note: This latter determination is within .02 of a foot of the contract head.
Average of the two methods, 62.375 ft.
This determination is .65 of 1 per cent, above the contract load.
THE DISPLACEMENT OF THE PLUNCERS.
The diameter given in the bid and indicated in the specifications submitted, was 25 in. for the water plungers; and the stroke was given at 24 in. As the dimensions needed verification before positive statements could be made, calibrations of the plunger diameter and stroke were made by means of steel tape and steel scale, made by concerns producing instruments of precision and well recognized as standard makers. The results were as follows:
Diameter of plungers found to be, 25 in.
Stroke of plungers found to be, 24 in.
Capacity of each plunger, per revolution of engine. 151 United States gallons.
Capacity of engine per revolution, 153 United States gallons.
YY eight of 1 cu. ft. of water at observed temperature of 44° F., 62.42 lb.
Weight of l gal. of water, 8.34 lb.
Weight of water per revolution of the engine at temperature noted, 1,276-02 lb.
THE WORK DONE BY THE PUMPING ENGINE.
Length of the duty test, ten hours.
Total weight of the water pumped in ten hours, 22,516,648.92 lh.
Total load against plungers, 62,175 ft.
Total work in ten hours, 1.404.475.976.185 ft. lh.
Net steam used in ten hours, 10.800.41 lb.
Duty of pumping engine per 1,000 lh. of dry steam as per contract requirements, 130,039,135 ft. lh.
Excess of duty above contract requirements, 8.16 per cent.
Work done by the main pumps, 71-horsepower.
Work done by the steam cylinders, 77.7horsepower.
Mechanical efficiency of machine. 90 per cent.
Steam per indicated horsepower per hour. 11.9 lh.
THE QUANTITY OF WATER PUMPED.
The average speed of the engine during the test run was 29.41 revolutions per minute: and at this rate the displacement of the plungers was 6.479,611 United States gallons per twenty-four hours. The limit of speed allowed bv the contract is 17.5 revolutions per minute anil at this speed the displacement would be 8.262,000 gal. per twenty-four hours, or a surplus delivery of about 1¾ per cent, at full speed. As the record of valve slippage for this type of engine with clear water is not over 1 per cent., and my own observations are to the effect that plunger leakage for outside packed plungers will not exceed one-tenth of one per cent., the excess of 3¼ per cent, will give a net delivery 2 per cent, more than the contract delivery at full speed.
CALIBRATIONS OF INSTRUMENTS ANU ELEMENTS.
Before the test was commenced the various substances and instruments were considered and their respective values agreed upon so that with an agreed reading throughout the test a unanimous decision would be reached when the test was finished. The determinations were as follows:
Weight of 1 cu. ft. of water at observed temperature 44“ F., 62.42 lb.
Pressure of 1 ft. of water per square inch at temperature, .43:547 lb.
Water column of steam gauge pipe above engine steam gauge, 3.04 lb.
Necessary reading of steam gauge during test to give engine the contract steam pressure of 120 lb., 123.04 lb.
Note: The average reading of steam gauge during test run was, 123.16 lb.
One foot of water at 44° F. taken according to Smithsonian institute is equal in mercury at 55° F. to .88488 of an inch.
Mercury at 55° F. for 1 lb. pressure, 1 in. sq., 2.041 in.
United States gallons per cubic foot of water, 7.48 gal.
Weight ot 1 gal. of water at 44° F., 8.34 lb.
ELEVATION OF VARIOUS POINTS.
To fix certain points of elevation so as to have data upon which to calculate at any time needed, certain points of elevation were observed and recorded as follows:
Under side of top nut on water gauge glass of receiving tank taking the water from the wells, 100.
Centre of water pressure gauge on gauge board of pumping engine, 111.58.
Datum line at mercury pressure gauge near engine water pressure gauge, 108.58.
DATA OF THE TEST.
The test commenced at 10:45 a. in. of Tuesday, June 9, 1908, and continued unintereuptedly until 8:45 p. m. of the same day; ten hours. A perfect record was obtained throughout the ten hours and the results given are a fair and extremely accurate expression of the performances of the pumping engine under the contract requirements. The readings were taken every twenty minutes and the averages were found to be as follows:
Steam pressure on engine gauge, 123.16 lb.
Vacuum by mercury column at condenser, 28.44 in.
First receiver, above atmosphere, 24.80 lb.
Second receiver above atmosphere, 0.30 lb.
Water pressure gauge. 11.99 lb.
Water pressure gauge, 27.57 ft.
Pressure mercury column, 27.31 in.
Below mercury gauge datum line, 11.40 in
Temperature at mercury pressure gauge, 98“ F.
Suction mercury column, 20.70 in.
Below datum, 3.00 in.
Temperature at suction mercury column. 68° F.
Temperature out of doors, 89“ F.
Diameter of high pressure cylinder, 14 in.
Diameter of intermediate cylinder, 24 in.
Diameter of low pressure cylinder, 36 in.
Diameter of each pump plunger, 25 in.
Stroke of all pistons and plungers 24 in
Average revolutions per minute, 29.41 in.
Average per minute, first twenty minutes, 27.65.
Average per minute, middle twenty minutes, 29.85.
Average per minute, last twenty minutes, 29.96.
This pumping engine is of the vertical, triple-expansion, crank and fly wheel, con densing type: with three outside packed single plungers. Each water plunger is rigidly connected to one of the steam pistons; and the three plungers are connected together as one pumping unit by means of connecting rods with cranks set at angles of 120 degrees from each other. The main pumps are of the separate plunger barrel pattern which 1 consider the best arrangement for this class of machinery; the main pump valve chambers being entirely separate and apart from the plunger barrels. The engine is self contained; no foundations being required aside from a solid concrete bed about level with the basement floor and extending beneath the entire water end of the machine. The main bed plates of the engine are supported upon the valve chambers of the main pumps, thus securing in a very rigid manner the water and steam ends of the machinery.
The upper works, or steam end of the pumping engine has steam cylinders of the Corliss type, with the steam and exhaust valves placed across the cylinder heads so as to reduce the clearance or waste room to the lowest practical limit with this type of steam valve. The cross heads are of annealed cast steel; the distance rods are of forged steel and connect the cross heads directly with the pump plungers in a thoroughly substantial and effective manner. The main cranks, one for the high pressure cylinder, two for the intermediate cylinder, and one for the low pressure cylinder, are of annealed cast steel. The main shafts and connecting rods are of forged steel, as also arc the piston rods. The connecting rods, plunger rods, main shafts, and piston rods are finished and polished. The valve gear is driven by eccentrics from the main shaft in a very effective, and thoroughly adjustable manner at all essential points. The fly wheels are about 9 ft. in diameter and according to their section of rim, dimensions of hub and arm, etc., will weigh between 8,000 and 9,000 lb.
The main engine bedplates are heavy in proportion to the engine and contain the pillow blocks for the main shafts, the shafts carrying the pillow blocks for the main shafts, the shafts carrying the two fly wheels. The main framing is of the round tower form, is heavy and in good proportion; the framing supports the cross head guides and is provided with wads and various projections for attaching all necessary appurtenances in a neat and thor ough manner. The condenser is of the surface type and, judging from the indications of the vacuum gauge, is well proportioned for the work; it maintains an exceptionally good and steady vacuum.
Altogether the pumping engine is heavy and strong and well calculated for the work to be done. It is of the most advanced type and probably superheated steam will increase the efficiency about 10 per cent, and, perhaps, at some future day further attention might be given to this line of practice. This new pumping engine is of type much favored and used by the leading cities of the country, and so far as now can be perceived will be of good and economical service for many years to come.