when dye-house is not running. If it be in summer time only about 50 H. P. of exhaust steam is required from receiver. If the initial pressure is 100 lbs., as it will be soon, the cut off on 32′′ cylinder at 0.3 and 44" cylinder at 0.5, the engine would develop about 950 H. P., and the amount of exhaust steam taken from re ceiver could equal about 50 H. P. The dye-house being stopped the full power of engine is not required.

Ordinary running in summer time requires about 1,000 H. P. from engine, and 450 H. P. of exhaust steam from receiver for the various heating purposes. With a cut-off of 0.40 in 32" cylinder, and 0.35 in 44′′ cylinder, the power developed would be about 1,050 H. P., and the required amount of exhaust steam could be taken from receiver.

Ordinary running in winter time requires about 1,000 H. P., and 600 H. P. of steam from the receiver for the various heating purposes. With 0.45 cut-off on 32'' cylinder, and 0.25 on 44" cylinder, the engine will develop about 1,030 H. P., and 600 H. P. of exhaust steam can be taken from receiver.

When extra steam power is required, either or both cylinders can be run as high pressure condensing.

The engine in its present condition is just one-half its proposed power when running compound, the full plan being, as additional power is required, to make it into a pair of tandem compounds, and when this is done the required amount of exhaust steam can be taken from the receiver with much shorter cut-offs on 32 inch cylinders than have been indicated above.

As we have been limited to 75 lbs. boiler pressure on the old boilers, we have run nearly all the time in winter with the 44 inch cylinder high pressure, and 32 inch low. The cards when running this way, with 83 per cent, of exhaust from 44 inch cylinder, taken from receiver for heating purposes, are shown on page 59.

Average per cent. taken from receiver for 7 months 450 1,000

= .45.

Average per cent. taken from receiver for 5 months 600 1,000

= .60.

Thus leaving 55% for 7 months to go into low pressure cylinder, and 40% for 5 months to go into low pressure cylinder.

3.75 x .49 = 1.84 ratio of areas of cylinders. It is intended to carry about 10 lbs. pressure in receiver.

CASE IV-A coarse cotton mill, dyeing about 75 per cent. of product in yarn and stock.

-

The actual figures for a year's run are given below. The coal consumption per 1,000 spindles per year for heating mills, dyeing and slashing was 90 tons Cumberland coal. If we take the amount required for heating and slashing at 18 tons per year per 1,000 spindles for coarse work, we shall have 90 18 = 72 tons per 1,000 spindles to charge to dye-house. 72 tons = 161,280 lbs. for 308 days 524 lbs. per day. About 20 per cent. of this is burned when engine would not be running, leaving 524 - 104.8 = 419.2 lbs. for 10 hours run = 41.92 lbs. per hour. 18 x .30 = 5.4 tons used for slashing 12,096 lbs. for 308 days = 39.3 lbs. per day 3.93 lbs. per hour.

=

41.92 + 3.93 = 45.85 lbs. per hour for slashing and dyeing for 7 months.

=

18. x.70 12.6 tons used for heating mills = 28,224 lbs. for 150 days 188 lbs. per day. About one-third of this would be burned when engine was not running, leaving 125 lbs. for 10 hours run, or 12.5 lbs. per hour.

=

45.85+ 12.5 58.35 lbs. for heating, dyeing and slashing for 5

68.08 lbs. at 2.85 lbs. coal per H. P. per hour 23.89, average equivalent H. P. of exhaust steam used throughout the year per 1,000 spindles.

The actual power required to drive everything, including dyehouse, was 27 H. P. per 1,000 spindles in this case.

23.89 27.88, or 88% of the exhaust steam can be used on an average for the entire year.

The proper type of engine to use in such a case as this would be a high pressure non-condensing, from which 84% of the exhaust steam could be used on an average throughout the entire year. In the above calculations various amounts of coal

per

H. P.

per

hour have been used, as has been shown in table I., page 50, which would be required for various per cents. of exhaust steam used, and all boiler pressures have been assumed at 100 lbs. per sq. in.

III. REGULATION OF RECEIVER PRESSURE.

As the amount of exhaust steam taken from the receiver is necessarily a variable if the cut-off in low pressure cylinder is constant, the receiver pressure must be a variable.

Under certain conditions the high pressure cylinder would regulate itself to the amount of exhaust steam and power required. Under other conditions it would not regulate itself, but in fact would work against regulation.

Supposing a slight increase above the average amount of exhaust steam is required, the pressure in receiver would decrease slightly, the work done in the low pressure cylinder would be decreased through loss of initial pressure and that in the high pressure cylinder increased by reduction of back pressure. If the relative areas of cylinders and cut-off in low pressure cylinder are such that the decrease of work done in the low pressure cylinder is greater than the increase of work done in the high pressure cylinder, then will the cut-off in high pressure cylinder increase to make up the deficiency in power and thus supply more exhaust steam, tending to bring the receiver pressure back to its normal condition and supply the draught from it.

In case, however, the relative areas of cylinders or cut-off in low pressure cylinder should be such that the decrcase of work in low pressure cylinder should be less than the increase of power in high pressure cylinder, then the cut-off in high pressure cylinder would decrease in order to produce the amount of power required, and thus the amount of exhaust steam would be decreased and the receiver pressure still further lowered, thus working directly opposite to the condition desired.

There is a liability of having unfavorable conditions for regulation in engines where the low pressure cylinder is large as compared with the high pressure, when steam is taken from the receiver; but when the areas of the two cylinders approach each other then the conditions unfavorable to automatic regulation, with constant cut-off in low pressure cylinder, will nearly always exist. This difficulty is overcome by arranging so that the cut-off on low pressure cylinder can be changed by hand at the will of the engineer who has to watch the gauge showing the receiver press

ure, and increase the cut-off on low pressure cylinder when the receiver pressure increases, and decrease the cut-off when the pressure decreases, the high pressure cylinder taking care of the work.

This arrangement is not wholly satisfactory, for when the amount taken from the receiver varies largely the pressure may change very much while the engineer is busy at his other work without his noticing the change, and then again he would not always stand ready to change the cut-off to suit the varying pressure in the receiver if he had nothing else to do.

The proper arrangement for supply where the amount used from

There should also be a relief valve on the low pressure system which will open in case all the steam exhausted from the high pressure cylinder is not used for heating purposes or in low pressure cylinder thus causing the pressure in receiver to increase.

In order to maintain a more nearly constant pressure in receiver than can be done by changing the cutoff on low pressure cylinder by hand, the writer has de

vised and applied to the engine at the Lower Pacific Mills the arrangement which is shown in Fig. 15. The working of this arrangement is as follows:

There is a small steam cylinder C in which is a piston P. The receiver pressure is admitted to the cylinder above the piston. The cylinder below the piston is open to the atmosphere. The piston rod R connects with the governor of the engine at H. Raising the point I shortens the cut-off on engine, and lowering the point H, lengthens the cut-off. To the rod is connected the arm A and on this arm are hung two weights W and W.

When the steam pressure is at its lowest admissible point in the receiver the cut-off on low pressure cylinder must be the shortest, and the piston must be at its highest position. The weight W is then vertically under the pivot at A and so has no leverage and no effect on the piston. When the piston and pressure are in these conditions the weight W is adjusted so that it will just balance the pressure on the piston, the weights of the piston, rods, etc., and the resistance to moving the same. Call this a constant weight, although it can be changed at any time for adjusting the cut-off. The weight of this is shown algebraically by the formula

where p

=

W = pxa+w+r

minimum pressure to be carried in receiver.

a = area of piston -area of piston-rod.

w= weight of piston, rods, etc.

r = resistance to moving piston, rods and governor.

The weight could be made equal to p × a + w and r could be determined by adding weights when the engine was running at speed.

When the steam is at its highest allowable pressure in the receiver, the piston is at its lowest point and the cut-off in low pressure cylinder must be the longest. The variation in pressure between the highest and lowest can be determined at pleasure by the weight W1, which in itself is constant but in effect variable by swinging from the vertical position of no leverage to some other position giving it leverage, thus balancing the variable pressure on piston. The weight of this is shown algebraically by the formula