Chapter 9

Approximately 34 feet was the static head of water to be pumped over No. 2 cooling tower. Pressure gages were connected to the suction, discharge, and condenser inlet, as shown at G, G' and G'' respectively. When No. 1 unit was operating alone the gage G showed practically zero, indicating no vacuum in the suction pipe. Observing the same gage when No. 2 unit was running, a vacuum as high as 2 pounds was indicated, showing that No. 2 was drawing more than its share of cooling water from the main A and hence the circulating pump for No. 1 was fighting for all it received. Gage G' indicated a pressure of 21 pounds, while G'' indicated 18.5 pounds, showing a difference of 2.5 pounds pressure lost in the S-bend. This is equivalent to a loss of head of nearly 6 feet, 0.43 pound per foot head being the constant employed. The total head against which the pump worked was therefore

G' + G = 21 + 2, or 23 ---- = 53 0.43

feet approximately. Since the static head was 34 feet, the head lost in friction was evidently

53-34 = 19 feet, or 1900 ---- = 36 53

per cent., approximately.

Supply of Cooling Water Limited

In addition to this the supply of cooling water was limited, the vacuum being extremely low at just the time when efficient operation should be had. The natural result occurred, which was this: As the load on the turbine increased, the amount of steam issuing into the condenser increased, beating [Transcriber: heating?] the circulating water to a temperature which the cooling tower (not in the best condition) was unable to decrease to any great extent. The vacuum gradually dropped off, which indicated that the condenser was being filled with vapor, and in a short time the small centrifugal tail-pump lost its prime, becoming "vapor bound," and the vacuum further decreased. The steam which had condensed would not go into the tail-pump because of the tendency of the dry-pump to maintain a vacuum. When a certain point was reached the dry-vacuum pump started to draw water in its cylinder, and the unit had to be shut down immediately.

Vapor-bound Pumps

As the circulating water gradually rose in temperature the circulating pump also became "vapor bound," so that the unit would be tied up for the rest of the night, as this pump could not be made to draw hot water. The reason for this condition may be explained in the following way. When the circulating pump was operating and there was a suction of 2 pounds indicated at G, the water was not flowing to the pump of its own accord, but was being pulled through by force. This water would flow through the pump until a point was reached when the water became hot enough to be converted into vapor, this occurring at a point where the pressure was sufficiently reduced to cause the water to boil. Naturally this point was in the suction pipe and vapor was thus maintained behind the pump as long as it was operating. In this case the pump was merely maintaining a partial vacuum, but not drawing water. After the vacuum was once lost, by reason of the facts given, it could not be regained, as the circulating water, piping and condenser required a considerable period of time in which to cool.

Before any radical changes were made it was decided that a man should crawl in the suction pipe A, and remove such sand, dirt, or any other obstacles as were believed to cause the friction. After this had been done and considerable sand had been removed, tests were resumed with practically the same results as before. The investigation was continued and the dry-vacuum pumps were overhauled, as they had been damaged by water in the cylinders, and furthermore needed re-boring. In short, the auxiliaries were restored to the best condition that could be brought about by the individual improvement of each piece of apparatus. As this was not the seat of the trouble, however, the remedy failed to effect a "cure." It was demonstrated that the steam consumption of the turbines was greatly increased due to priming of the boilers, as well as condensation in the turbine casing; hence, the ills above mentioned were aggravated.

Changes in Piping

After a great deal of argument from the chief engineer, and the firm which furnished the pump, both making a strong plea for a change in the piping, the company accepted the inevitable, and the dotted portion shows the present layout. The elbow M was removed, and a tee put in its place to which the piping D was connected. The circulating pump was removed to the position shown, and a direct connection substituted for the S-bend. The discharge pipe C was carried from No. 1 unit separately, as shown in the elevation, and terminated at No. 1 cooling tower instead of No. 2, which shortened the distance about 60 feet, the total length of pipe (one way) from No. 1 unit being originally 250 feet. In this way the condensing equipment was made practically separate for each turbine, as it should have been in the first place.

With the new piping a vacuum of 24 inches on the peak could be reached. While this is far from an efficient value, yet it is better than the former figure. The failure to reach a vacuum of 28 inches or better is due primarily to a lack of cooling water, but an improvement in this regard could be made by reconstructing the cooling towers, which at present do not offer the proper amount of cooling surface. The screens used were heavy galvanized wire of about 3/16-inch mesh, which became coated in a short time, and must be thoroughly cleaned to permit the water to drop through them. The supply of cooling water was taken from a 30-inch pipe line several miles long and fed from a spring. The amount of water varied considerably and was at times quite insufficient for the load on the plant. Instead of meeting this condition with the best apparatus possible, a chain of difficulties were added to it, with the results given.

INDEX

Acceleration, rate of, 147

Adjustment, axial, 65 making, 66

Air-pump, examining, 163

Allis-Chalmers Co. steam turbine, 41

Auxiliaries, 2, 154 special, 165

Auxiliary plant for consumption test, 137 spring on governor dome, 28

Axial adjustment, 65

Baffler, 36 functions, 39

Bearings, main, 69

Blades, construction details, 44 inspecting, 104

Blading, Allis-Chalmers turbine, 48 Westinghouse-Parsons turbine, 59, 92

Blueprints, studying, 11

Buckets, moving, 14 stationary, 14

Bushings, 36

Carbon packing, 19 ring, 20

Central gravity oiling system, 111

Circulating pump fails to meet guarantee, 172

Clearance, 15, 150 adjusting, 18 between moving and stationary buckets, 4 gages, 17 measuring, 18 radial, 63

Comma lashing, 95

Condensers, 108, 131 jet, 154

Conditions for successful operation, 105

Cooling water supply limited, 177

Coupling, 127

Cover-plate, 4 -plate, lowering, 9

Curtis turbine, 11 turbine in practice, 1 setting valves, 31, 32

De Laval turbines, 118

Draining system, 105

Dummy leakage, 115 pistons, 63, 65 rings, 43, 113, 114

Equalizing pipes, 64

Exhaust end of turbine, 107 pipe, 107

Expanding nozzles, 14

Feed-pipes, 164

Flow, rate, 38

Foundation drawings, 2 rings, 44, 46

Fourth-stage wheel, 14

Franklin, Thomas, 112, 137, 154

Gages, calibrating and adjusting, 169 clearance, 17 for test work, 165

Generator, 53

Glands, examination for scale, 104 packing, 71, 77 regulation, 148

Governor, Allis-Chalmers turbine, 48 Curtis turbine, 27, 31 improved, Westinghouse-Parsons turbine, 83 -rods, adjusting, 35 safety-stop, 86 Westinghouse-Parsons turbine, 80

Grinding, 38

Guide-bearing, lower, 9

Gump, Walter B., 172

Holly draining system, 106

Horseshoe shim, 8

Hot-well regulation, 148

Inspection, 103

Intermediate, 14

Jacking ring, 8

Jet condenser, 154

Johnson, Fred L., 1, 31

Leakage, 118

Load variation, 144

Lower guide-bearing, 9

Lubrication, 51

Measuring tanks, 171

Mechanical valve-gear, 32

Nozzles, expanding, 14

Oil, 57, 103, 109 amount passing through bearings, 122 consumption, high, 175 detecting water in, 122 pressure, 122 -temperature curve, 123

Oil, testing, 110 velocity of flow, 122

Oiling, 87 system, importance, 119

Operation, Allis-Chalmers turbine, 54, 55 successful, 105

Operations in handling turbine plant, 146

Overload valve, 28

Packing, carbon, 19 glands, 71 ring, self-centering, 14

Parsons type of turbine, 41

Passage in foundation, 2

Peep-holes, 15, 18

Piping, 171 changing, 179 inspection, 164

Pressure, 63 gages, 166 in glands, 57

Pump, circulating, fails to meet guarantee, 172 inspection, 164

Radial clearance, 63

Rateau turbines, 118

Relief valves, 31 valves, importance, 159

Ring, carbon, 20

Rotor, Westinghouse-Parsons turbine, 59

Running, 99

Safety-stop, 22 -stop governor, 86

Saucer steps, 39

Screw, step-bearing, 18 step-supporting, 4

Separators, 105

Setting spindle and cylinder for minimum leakage, 115 valves in Curtis turbine, 31, 32

Shaft, holding up while removing support, 8

Shield-plate, 26, 36

Shim, horseshoe, 8

Shroud rings, 44, 46

Shrouding on buckets and intermediates, 18

Shutting down, 101

Special turbine features, 127

Spindle, lifting, 96 removing, 104

Spraying mechanism, 158

Stage valves, 28, 31

Starting up, 54, 95

Step-bearing, lowering to examine, 8 -bearing screw, 18 -blocks, 4 -lubricant, 4 -pressure, 38 -supporting screw, 4 -water, flow, 38

Stopping turbine, 56

Sub-base, 8

Superheated steam, 105

Test loads, 141 necessary features, 163

Testing oil, 110 preparing turbine for, 145 steam turbine, 112, 137, 152

Thermometer, calibrating and testing, 169 oil, 125

Thrust-block, 118

Top block, 4

Troubles with steam turbine auxiliaries, 172

Turbine features, special, 127

Vacuum, 152 raising, 107 test, 135

Valve-gear, 83 -gear, mechanical, 22, 32 operation during consumption test, 138 overload, 28 relief, 31 importance, 159 setting in Curtis turbine, 31, 32 stage, 28,31

Vapor bound pumps, 178

Water, cooling, limited, 177 in oil, detecting, 122 -measurement readings, 148 pressure, 101 service, 126 importance, 119 tests of condenser, 133 used in glands, 57, 76

Westinghouse-Parsons steam turbine, 58

Wheels, 14 lower or fourth-stage, 14 position, 18