Where Thermometers are Required

Equally important with the foregoing is the necessity of calibrating and testing of all thermometers used during a test. Where possible it is advisable to place new thermometers which have been previously tested at all points of high temperature. Briefly running them over, the points at which it is necessary to place thermometers in the entire system of the steam and condensing plant are as follows:

  1. (1) A thermometer in the steam pipe on the boiler, where the pipe leaves the superheater.
  2. (2) In the steam pipe immediately in front of the main stop-valve, near point E in Fig. [75].
  3. (3) In the main governing valve body (see I, Fig. [75]) on the inlet side.
  4. (4) In the main governing valve body on the turbine side, which will register temperatures of steam after it has passed through the valve.
  5. (5) In the steam-turbine high-pressure chamber, giving the temperature of the steam before it has passed through any blades.
  6. (6) In the exhaust chamber, giving the temperature of steam on leaving the last row of blades.
  7. (7) In the exhaust pipe near the condenser.
  8. (8) In the condenser body.
  9. (9) In the circulating-water inlet pipe close to the condenser.
  10. (10) In the circulating-water outlet pipe close to the condenser.
  11. (11) In the air-pump suction pipe close to the condenser.
  12. (12) In the air-pump suction pipe close to the air pump.

It is not advisable to place at those vital points, the readings at which directly or indirectly affect the consumption, two thermometers, say one ordinary chemical thermometer and one thermometer of the gage type, thus eliminating the possibility of any doubt which might exist were only one thermometer placed there.

There is no apparent reason why one should attempt to take a series of temperature readings during a consumption test on varying load. The temperatures registered under a steady load test can be obtained with great reliability, but on a varying load, with constantly changing temperatures at all points, this is impossible. This is, of course, owing to the natural sluggishness of the temperature-recording instruments, of whatever class they belong to, in responding to changes of condition. As a matter of fact, the possibility of obtaining correctly the entire conditions in a system running under greatly varying loads is very doubtful indeed, and consequently great reliance cannot be placed upon figures obtained under such conditions.

A few simple calculations will reveal to the tester his special requirements in the direction of measuring tanks, piping, etc., for his steam consumption test. Thus, assuming the turbine to be tested to be of 3000 kilowatt capacity normal load, with a guaranteed steam consumption of, say, 14.5 pounds per kilowatt-hour, he calculates the total water rate per hour, which in this case would be 43,500 pounds, and designs his weighing or measuring tanks to cope with that amount, allowing, of course, a marginal tank volume for overload requirements.

VIII. TROUBLES WITH STEAM TURBINE AUXILIARIES[7]

[7] Contributed to Power by Walter B. Gump.

The case about to be described concerns a steam plant in which there were seven cross-compound condensing Corliss engines, and two Curtis steam turbines. The latter were each of 1500-kilowatt capacity, and were connected to surface condensers, dry-vacuum pumps, centrifugal, hot-well and circulating pumps, respectively. In the illustration (Fig. [76]), the original lay-out of piping is shown in full lines. Being originally a reciprocating plant it was difficult to make the allotted space for the turbines suitable for their proper installation. The trouble which followed was a perfectly natural result of the failure to meet the requirements of a turbine plant, and the description herein given is but one example of a great many where the executive head of a concern insists upon controlling the situation without regard to engineering advice or common sense.