WATER WORKS FROM FIRE AND INSURANCE STANDPOINTS

Joseph B. Rider
  -

WATER WORKS FROM FIRE AND INSURANCE STANDPOINTS*

(Continued from page 212.)

Water Available for Fire Use From a Gravity Water Works:

Example No. 10—We will assume the same pipe line system as shown on Sketch No. I, and that instead of a pumping system, a reservoir of ample dimensions is located on a hill or formed by a dam across a valley at pumping station location hereinbefore considered and at such elevation as to give eighty pounds of static† pressure in the business center.

By Table D we find 80 pounds = 185 feet head, approximately. Therefore, the reservoir is 185 feet above the business center. Hydraulic Grade—

We will assume that the first 5,000 feet of the 16-inch main from the reservoir is laid across a flat country, on a grade of 0.15 per too feet = 1.5 per 1,000 feet = 7.5 feet in 5,000 feet.

By Table D we have 1.5 feet per 1,000 feet (the total fall in 1,000 feet) corresponds to 1.5 X 0.433 = 0.649, say 0.65 pound pressure lost per 1,000 feet when the line is delivering its maximum amount of water on this grade, without any head over pipe in reservoir except for proper influx of water.

Looking in Table H under 16 inches we find this loss of head opposite 1,600 gallons per minute, as the maximum amount of water that can be delivered per minute = 1,304,000 gallons per day.

Under example No. 3 we found the equivalent length of our main line to Wilson Avenue to be 64,250 feet of 16 inch. Therefore, in delivering to the business center the maximum capacity of the upper end of the 16-inch line, or 1,600 g.m., we would lose 64.25 X 0.65 pounds = 41.76 pounds, say 42 pounds which, taken from 80 pounds, our normal pressure, leaves but 38 pounds at the hydrants. This is too low a pressure for direct fire streams without use of engines.

We ought not to have less than 50 pounds net at the hydrants. This would allow 80 — 50 = 30 pounds for loss in main line friction in equivalent of 64,250 feet, or say in 65,000 feet = 0.461 pounds per 1,000 feet. Looking in Table H under 16 inches we find 0.44 opposite 1,300 g.m., or slightly in excess of r.300 g.m. is the maximum amount of water per minute we can deliver under 50 pounds in the business center under a static head = 80 pounds, with no allowance for loss in hydrant branches.

In the above we have 185feet fall from reservoir to the business center in a pipe line the equivalent length of which is 64.5 thousand feet of 16 inch; the rate of average grade or fall is therefore 2.87 feet per 1,000 feet. If there was no point of the pipe line above this imaginary grade line, our maximum delivery under no pressure head at the outlets or hdyrants would be as follows:

2.87 feet X 0.433 (by Table D) = 1.242 pounds loss in pressure per 1,000 feet. By Table H we have 0.945 pounds per 2,000 g.m. and 1.43 pounds for 2,500 g.m. By proportion we have, therefore, 1.242 corresponding with 2.305 gallons per minute as the maximum delivery of the line if laid below “hydraulic grade,” or 705 gallons per minute greater in maximum capacity than if the upper end is laid on flat grade of t.5 feet per 1,000 feet, as assumed. But it is assumed as laid on grade below that necessary to give discharge under 50 pounds pressure of 1,300 g.m. or below a (0.44 X 2.31) — 1.016 per 1,000 feet grade.

Suppose we assume we want a hydrant working pressure of 40 pounds at the Old Ladies Home (see Example No. 6. Fire No. 2) from the reservoir with the static pressure at 58 pounds, what quantity of water can we obtain ?

Static pressure . 58 lbs.

Working pressure .. 40 “

Difference . 18 “ to be lost in friction in a line the equivalent length of which was found to be 364,000 feet of 16 inch, or a loss of 0.0438 per 1,000 feet, or say 0.044 per 1,000 feet, and which we find by Table H to correspond with a flow of 350 gallons per minute, or two small fire streams, each through about 150 feet of 2 1/2-inch hose, with I-inch nozzles, with about 32 pounds nozzle pressure, with the streams being thrown about 50 to 60 feet, depending on the wind. If the supply is by gravity this is too small a delivery to properly protect; and the line on Congress Street should have been at least 8-inch. Supply By Gravity Without Use of Fire Engines.

Fire No. 6—Let us assume Fire No. 6 to occur in a church at the corner of Wilson and West Avenue and that hydrant No. 17 is in use, and that the only line feeding the same is 16 inch from reservoir to Congress Street, or 15,000 feet of 16 inch, then 8,500 feet of 8 inch on West Avenue, and that we want a working pressure of 50 pounds.

We have, by Table G:

15,000 feet 16 inch = 15,000 ft. 16 in.

8,500 feet 8 inch = 8,500 X

28.8 = 244,800 “ “

Equivalent line in 16 inch 259,800 “

Or say 260,000 ft. 16 in.

Assuming static pressure at 80 pounds, we have 80 — 50 = 30 pounds as loss in friction. Assuming delivery at 700 g.m. our loss in hydrants and branch, as per previous assumptions, would be 3.5 pounds, leaving 26.5 pounds as loss in pipe line, or say 26 pounds, 26 / 260 = 0.1 pound per 1,000 feet. Looking in Table H we find 0.11 for 600 g.m., or, with final corrections for flow of 600 instead of 700 g.m. through hydrant and branch, we have a flow of nearly 600 g.m., or about three fair fire streams through reasonable lengths of hose, as considered in Part 2.

Delivery From Reservoir and Standpipe Simultaneously.

Now suppose at this same fire we are having water delivered through the above considered 16 inch-8 inch line from the reservoir and from a standpipe 15 feet in diameter and high enough to give the same 80 pounds static pressure and situated 2,000 feet southerly (off the sketch) from hydrant No. 17; what would be the delivery under 50 pounds working pressure?

It is evident that the pipe line from the reservoir and the one from the standpipe will act as independent lines, each with a total loss in pressure of 30 pounds and which loss in each case will be divided between loss in main friction and in hydrant branches and. hydrants.

At first let us eliminate the loss in hydrant and branch in order to find directly an approximate—yet high discharge.

In the case of the 8-inch line we have a total loss of 30 pounds, or 15 pounds per 1,000 feet, and without loss in hydrant and branch, by Table H. we have a little over 1,400 g.m.

In the case of the 16 inch-8 inch line from the reservoir, we have 30 / 260 — 0.115 pounds loss per 1,000 feet, and by Table H this corresponds with a flow of 600 “

Total discharge 2,000 “

without considering loss in hydrant and branch.

As we see that the flow from the standpipe will be a little over double that from the reservoir, we can assume that the loss twothirded of the loss in hydrant and branch will be chargeable to the standpipe line and onethird to the reservoir line, or assuming a total flow of 1,800 g.m. under the conditions, a 0.5 per 100 gallons flow, we would have a total loss of 9 pounds, of which 6 pounds would be for standpipe line and 3 pounds for reservoir line. Deducting, we have: 30 — 6 = 24 pounds per 1,000 feet for standpipe line, and 27 pounds / 260= 0.104 for reservoir line per r,ooo feet.

By Table H we have:

Discharge for 8-inch line (use proportion) 1,155 g.m.

Discharge for 16 inch-8 inch line

(use proportion) 580 “

Total discharge under 50 pounds net pressure 1,735 g.m.

Or in as close agreement with our assumed discharge of 1,800 as possible, or prudent to suggest, for no two pipe lines are alike in discharging capacity, due to good and bad laying, different makes of hydrants, etc.

The solution of the problems presented by fires No. 7 at G, and No. 8 at H, are left to those interested, both with and without the local standpipe, assumed in various locations.

Proper use of the tables and data will permit of the solution of almost any problem of flow in pipe lines with a degree of accuracy quite sufficient in most cases.

* Examples showing some uses of Tables G and H, etc., on page 820. See map on page 212.

† Normal pressure is less than static, depending on amount of flow for ordinary uses, exclusive of fire stream flow.

Copyright, 1914, by J. B. Rider.

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WATER WORKS FROM FIRE AND INSURANCE STANDPOINTS

1

WATER WORKS FROM FIRE AND INSURANCE STANDPOINTS’

Example No. 7. Fire No. 3.—We will assume that a private water company constructed the original water works, since purchased by the city, and like many such companies, they did not look or plan very far into the future. At the tune the works were constructed the easterly end of Congress street (see sketch No. 1) offered little inducement to the water company to lay a large main as each house or shack was occupied by negroes; hence but a 4-inch pipe line was laid to supply domestic wants, and little pretense made at fire protection. The city recently greeted the municipal electric plant at the end of the street, on the shore of Bryan River, m order to take advantage of the river water for condensing purposes. What, if any, fire protection can they obtain,? the length of trie 4-inch line from Main street being 2,500 feet, and the normal pressure being 93. pounds, the point being 30 feet lower than the business center, where the pressure is 80 pounds.

The 16-inch main line being large in proportion to the 4-inch, we will assume that 3 pounds will be enough to allow for loss of head in the 16-inch and thus leave 90 pounds for total loss in the 4-inch line.

If 90 pounds is to be lost in 2,500 feet, we can s.and a loss of 90+2.5 per 1,000 feet=34.6 pounds per 1,000 feet.

Looking in Table H, under 4-inch we find 34.5 pounds for 350 gallons per minute per 1,000 feet of 4-inch main as the loss; therefore our assumed loss represents a delivery of 350 gallons per minute. Now we have left but three pounds for loss in hydrant and connection and in flow through 16-inch main.

Looking at Table H under 16-inch, we find the loss per 1,000 feet for a flow of 350 gallons per minute to be 0.044 pounds, or for the 15,000 feet of 16-inch main to the corner of Congress street, we would have a loss of 15×0.044 pounds:=0.66 pound or say 0.7 pound.

Deducting this front 3.0 pounds, we have 2.3 pounds, about enough to allow for drop in pressure in passing the water through the hydrant branch and hydrant; all will depend on how well the 4-inch line was laid; if crooked, up and down and sidewise, etc., as laid by many contractors, it would not be safe to count on over 300 gallons per minute; if laid to true line and grade we would have no trouble in obtaining 350 or more gallons per minute under the circumstances.

The only thing we can do in this case if the electric works takes fire is to put our small No. 3 engine of 500 gallons per minute capacity at work at slow speed, taking water from hydrant No. 12, and use No. 1 engine of 1,000 gallons per minute and No. 2 engine of 500 gallons per minute at work pumping from the Bryan River. The 4-inch main is entirely too small and long to give fire protection worthy the name.

If an attempt should be made to work No. 3 engine at full capacity it is more than probable that the long 2,500 foot column of water in the 4-inch line would “strip” and the engine would lose its suction, and cease to pump and deliver water.

Example No. 8; Fire No. 4—Compound discharge, with water being delivered through two pipe lines simultaneously; required to determine the drop from normal to working pres, sure and the amount of flow through each pipe line:

* Examples showing some rises of Tables G and H, etc., on page 329.

Capyright, 1914, by J. B. Rider.

We will assume that Fire No. 4 at D is of moderate size for the city and that we will require but 1,500 g.m. of water, and that hydrants Nos. 14 and 21 at the corner of Wall Street and West Avenue are available; hydrant No. 21 being a private hydrant in the factory yard.

A glance at Sketch No. 1 will show that the flow, if the valves are open, will be diverted at Congress Street and part flow down Main Street and the remainder down West Avenue, if we neglect, as we can, such small flow as might in case of “heavy draft” of water flow via of East Avenue. The distance between street centers is assumed at 1,000 feet, the intervening streets for the sake of clearness not being shown.

We will allow a safety factor in our computations by neglecting the tendency of water to flow through the laterals from Main Street to West Avenue during the progress of the fire, except that of the flow through the Wall Street line which will be in use.

To find the loss or drop in pressure to Congress Street:—By aid of Table H we find under 16 inch and opposite 1,500 g.m. the loss per 1,000 feet to be 0.576 pounds. In 15,000 feet 16 inches to Congress Street we have 15 X 0.576 lbs. = 8.64 lbs., which loss must be finally deducted.

Our largest size main below Congress Street through which water will be flowing is 12 inches; hence we reduce both line to lines of this diameter and find out their equivalent length by Table G, as follows:

West Avenue Line:

Length from Congress Street to hydrant No. 14 = 7,000 ft. 8 in.

7,000 X 7.1 (by table G) = 49,700 ft. 12 in.

in delivering capacity.

We note by inspection that the 12-inch equivalent of the Main-Wall Street line is about one-third the length of the other line. Without entering a discussion of the complicated problems of flow with a mathematical consideration, which would be here out of place, as a guide we will assume that one-third in this case would come through the West Avenue line, the equivalent of which was found to be 49,700 feet of 12 inch; one third of 1,500 g.m. = 500 g.m. Opposite 500 g.m. and under 12 inches in Table H we find 0.32 lb. loss pet 1,000 feet, or a loss of 15.9 pounds in a line the equivalent length of which is 49,700 feet 12 inches.

We will assume the remainder of the 1,500 g.m., or 1,000 g.m., will be delivered through the Main-Wall Street line, the equivalent length of which was found to be 17,000 feet of 12 inch.

In Table G. under 12 inch and opposite 1,000 g.m. we find 1.1 pounds as the loss per 1.000 feet. In 17,000 feet we would therefore lose, on the above assumption, 17 X 1.1 pounds = 18.7 pounds.

This is greater by 2.8 pounds than 15.9 pounds, the loss just before determined for

the West Avenue line, but is near enough for ail practical purposes.

It simply means that a little over 500 g.m. will be delivered by way of the West Avenue line, and a little under, 1,000 g.m. will come by way of the Main Street-Wall Street line.

To increase the bulk of the table by giving factors for every to, 25 or 50 gallons per minute would be an unnecessary refinement in cases of this nature; for what we want to know is the result within one fire stream, so as to know how many lines of hose to lay from either hydrant or pipe line. In all cases under 1,000 g.m. the table will do this; and within one or two streams above this quantity; but in any case from the data given the result can be obtained with a fair degree of accuracy by proportion. If in any case there is too much difference in the two results in pressure lost, try again, using the next highest figure in the table for the smaller delivery and the next lower for the greater delivery, or use proportion.

Adding one-half the above difference in lost pressure of 0.5 X 2.8 pounds = 1.4 pounds to the lowest determination, we have 15.9 pounds + 1.4 pounds = 17.3 pounds, as approximate loss below Congress Street.

Assuming normal pressure at West Avenue and Wall Street at 85.00 pounds, we have: Loss to Congress Street, as before

determined……… 8.64 lbs.

Leaving a net working pressure of 50. “

Example 9; Fire No. 5—This fire is supposed to be at E, at the westerly end of Wall Street, in a planing mill and lumber yard.

The most available hydrant is No. 20, and to which is first attached our A No. 1, 1,000 g.m. engine. Hydrant No. 20 being at the end of a 1,500 foot line of 6 inch from West Avenue corner where we assumed fire No. 4 to have occurred.

We will also place our engine from the hill, of 500 g.m. capacity, at hydrant No. 19, distant 1,000 feet from West Avenue.

We will assume the normal pressure at 85 pounds, or the same as at Wall Street and West Avenue.

By Table H we have: Loss in 1,000 g.m. delivery 1,500 feet (1.5 X 1,000) to engine at hydrant No. 20, 32 x 1.5 = 48 pounds.

We will now place our engine from the hill, 500 g.m. capacity, so as to take water from hydrant No. 19, distant on the 6-inch main 1,000 feet from West Avenue.

In the previous example we found the losses to the corner of Wall Street and West Avenue to be for the same quantity (1,500 g.m.), as follows:

Loss to Congress St. in 16-inch main 8.64 lbs.

Loss below Congress

St. 17-3 “

Adding losses in hydrant branches and hydrants, the same in this case as in the preceding, or 7.5 + 2.0 lbs. = 9.5 “

Say 35 lbs., and which must be added to the above 35-oo

Total losses or drop in pressure = 92.00 As our total normal pressure is but 85.00

Difference or excess use over that

available 7.00

Assuming that the pressure at the pump station has not been increased during the fire, this brings about an impossible situation, for engine at hydrant No. 20 cannot obtain 1,000 gallons per minute, for this quantity will not flow past engine No. 2 at hydrant No. 19. There will be a serious tendency for No. 1 engine to lose its suction, unless delivery is immediately cut down on starting up engine No. 2.

Our engines have been badly placed; now we can either keep No. 2 working from hydrant No. 19, until we can move No. 1 to this hydrant and then place No. 2 at hydrant No. 20, or if the fire is serious we should keep No. 1 where it is and run it at. 50 per cent, capacity or 500 g.m., keeping No. 2 at work delivering 500 g.m. and call in No. 3 engine and hook it up to No. 19 hydrant alongside of No. 2 engine if the delivery to the hydrant is enough to do so; if not hook it up to No. 18 hydrant, but let us assume it connected up to No. 19 hydrant.

We then have changed matters around and will be delivering 1,000 g.m. through 1,000 feet of 6-inch pipe line and 500 g.m. through 1,500 feet of 6-inch pipe line, instead of trying to deliver t.ooo gallons per minute through 1,500 feet and 500 g.m. through 1,000 feet of 6-inch pipe line. Let us see what results.

By aid of Table H we have:

Loss for 1,000 g.m. in 1,000 feet

6 inch = 32.0 lbs.

Loss for 500 g.m. in 1,500 feet 6 inch = 9.2 + (0.5 X 9-2) =13.8 “

Total loss for Wall Street 6-inch line west of West Avenue 45.8 “

Adding losses to Wall and West Avenue and loss in hydrants and branches, as above 35.0 “

Total losses in delivering 1,500 g.m.

at fire = 80.8

Or say 81.0 “

As our normal pressure is 85 pounds, we have a “leeway” of four pounds by properly placing the engines; while in placing as at first attempted we lacked seven pounds of the requisite pressure, of being able to deliver this amount of water.

Place your engines as near as possible to the large main, and in this way often a small lateral pipe line will deliver sufficient water for a fire, while if poor judgment is used, as herein at several points considered, heavy fire loss will result through not getting the maximum amount of water available for fire engines, and through putting some of them out of service by attempting to make them “suck” and deliver “wind” and not water.

In all of the preceding examples we have assumed a direct pumping water system to be in use and that the pressure on the mains during a fire has not been increased, but that pressure has been maintained at normal of 90 pounds at the pump station, giving 80 pounds normal in the business center, when fire streams are not in use; in other words, pumps have been speeded up to just equal demand for fire engine use assumed in each case, with normal pressure at pumps maintained at 90 pounds.

(To be continued.)

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