SAN FRANCISCO’S AUXILIARY SYSTEM
High Pressure Water Supply System for Fire Protection—One High Pressure Hydrant Gives More Water than Three Fire Engines—Fire Cisterns as Reserve in Case Hydrants are Not Available
SAN FRANCISCO has an auxiliary water supply system for fire protection only. It consists of a distributing system filled with fresh water under a high pressure, fed by gravity from tanks and a large storage reservoir, and is connected with two pumping stations on the Bay shore capable of pumping salt water directly into the system. This distributing system consists of a network of pipes which gridiron the city’s thickly built-up district and gives fire protection to an area of about 9 1/2 square miles. As a protection to the piers and filled-in areas along the waterfront and to shipping in the harbor, two fire-boats have been constructed. These boats are capable of being connected with the distributing system by means of two manifolds placed at convenient points so that the boats can pump salt water from the Bay into the distributing system. A total of 141 concrete fire cisterns have been built in the streets at various points throughout the city, even outside of the district covered by the system of high pressure pipe lines.
These cisterns are kept full of fresh water and are to be used in case the hydrants are not available. The water supply system for domestic purposes, which is entirely independent of the system herein described, is connected with low pressure hydrants throughout the city, and thus gives an additional protection in the congested area. A lire alarm system has been built in connection with the auxiliary water supply system, with a centrally located fire alarm station.
Work on the auxiliary water supply system was started in 1909. and was completed under the direction of M. M. O’Shaughnessy, the present city engineer, by the end of 1913. The total cost of the system was $5,756,000, and the annual saving in insurance amounts to over $1,400,000.
The distributing system consists of 74.5 miles of heavy weight cast iron pipe. This pipe is substantially in accordance with the specifications of the New England Water Works Association, and was tested at the factories. In testing the pipe lines a leakage of one gallon of water per 24 hours for each lineal foot of joint measured on the inside circumference of the pipe was allowed. The pipe varies in size from 20 inches diameter to 8 inches diameter, with an average diameter of 14 inches. The 8-inch pipe is used in the leads from the mains in the streets to the hydrants only. All of the pipe is of the bell and spigot variety, except in certain areas, four in number, where the pipe is laid on filled ground, and in order to give more play in the joints in case of an earthquake or a settlement of the ground, double spigot pipe is laid in these areas, which are cut off from the pipe on firm ground by means of closed valves, one valve being left open near a fire station to feed into the area.
As San Francisco is built mainly on a series of hills, in order to allow for the difference in elevation it was found necessary to divide the system into two zones, called the “Upper Zone” and the “Lower Zone.” The upper zone is that portion which lies above the 150 foot level, and the lower zone is that portion which lies below the 150 foot level. The upper zone is cut off from the lower zone by closed valves. Each zone is supplied by means of separate tanks. A large reservoir, called the Twin Peaks Reservoir, has been placed at a high elevation and connects with the upper and lower zones and with the upper zone tank by means of pipes leading directly front it, which are ordinarily shut off by closed valves, which can be opened in case of a large conflagration or a fire requiring a greater pressure than the tank elevation will give. Where the pipes lines cross each other at street intersections connection is made by means of crosses, and four valves are placed, one at each property line, so that any block can be cut off from the rest of the system in case of a break in that block.
There are 907 hydrants in the system, each hydrant having three outlets of 3 1/2 inches diameter, two of the outlets being reduced to 3 inches diameter. The average pressure at the hydrants in the upper zone is 130 lbs. per square inch and in the lower zone 143 lbs. per square inch.
The valves are of the parallel face disc non-rising stem type, bronze lined, and are 2 inches smaller in diameter than the mains in all sizes over 10 inches. The 16and 18-inch valves have 3and 4-inch by-pass valves, respectively, and are capable of being laid vertically or horizontally, the horizontal position requiring a different headgear and by-pass valve than the vertical position. Valves over 10 inches in diameter are placed in reinforced concrete manholes, and the 8and 10-inch valves are set in the ground,, the 8-inch valve having a 6-inch pipe riser and the 10-inch valve a concrete cone riser.
A storage reservoir of 10,000,000 gallons capacity is located on Twin Peaks. The water elevation is 758 feet. It is elliptical in shape, with axes of 375 feet and 280 feet. The side slopes are two horizontally to one vertically, and the depth of the water is 25 feet. The sides and bottom are lined with reinforced concrete slabs with expansion joints between each slab. It is divided into two equal bays by means of a reinforced concrete division wall, heavily buttressed on each side. Each bay has a separate forebay and gate chamber. The two forebays are connected by a 20-inch pipe, with sluice gates at each end. and the two gate chambers are connected by a 20-inch pipe with gate valves at each end. Each bay has a 20-inch pipe leading from it to the upper zone tank and the zone. It is cut off from the distributing system, however, by means of closed valves in these 20-inch pipes, which are opened only in case of emergency. The reservoir is filled from the upper zone tank by two electrically-driven centrifugal pumps located at the tank, each pump having a capacity of 700 gallons per minute.
Upper Zone Tank
This is ordinarily called the Asbury Heights tank and is located on Asbury Street, between 17th and 18th Streets. It is of steel plate construction on a reinforced concrete base, and is 55 feet in diameter by 29′ 1/2” high, with a capacity of 500,000 gallons. The elevation of the water level is 493.5 feet. There are three 18-inch pipes leading from it into the upper zone system, and it is filled by gravity through a 6-inch pipe connected with the Clarendon Heights tank of the Spring Valley Water Company. A reinforced concrete gate house is located in front of the tank.
Lower Zone Tank
This is also called the Jones Street tank, and is located on Jones Street, between Sacramento and Clay Streets. It is of reinforced concrete construction, with a capacity of 750,000 gallons. The inside diameter is 60 feet and the height is 35 feet 10 inches. The water level is 369 feet.
The lower zone is supplied from this tank by two 18inch pipes. This tank can be by-passed and the lower zone supplied from the upper zone, if necessary. I he tank is filled by gravity through a 6-inch pipe leading from the Clay Street tank of the Spring Valley Water Company. There is a reinforced concrete gate house connected with the tank, with a fireman in attendance.
Pumping Station No. 1
This station is located at Second and Townsend Streets, near the southern end of the distributing system and is designed for pumping salt water from the Bay into the system. The building is of reinforced concrete construction. built on solid rock, and is designed especially to withstand earthquakes and is said to be the most substantial building in San Francisco.
It is equipped with four sets of multi-stage turbine pumps direct connected to 750 HP horizontal non-condensing steam turbines of the Curtiss type, each set having a guaranteed capacity of 2,700 gallons and an actual capacity of 3,000 gallons of salt water per minute against a head of 300 lbs. per square inch. The pumps are supplied by means of a reinforced concrete tunnel, 6 feet in diameter, leading from the bay. The pump suctions are 12 inches in diameter and have a lift of 15 feet. They discharge directly into the lower zone system through two 20-inch pipes. There are eight 350 H. P. Babcock & Wilcox boilers. These boilers are set in four batteries of two boilers each and are enclosed in brick and steel airtight casings. A separate reinforced concrete smokestack, 68 inches in diameter by 90 feet high above the engine room floor, is connected to each battery. The boilers are arranged for burning fuel oil and storage tanks having a capacity of 2,000 barrels of oil are situated under the street outside of the building.
The basement has been excavated to a proper depth to provide for six rectangular reinforced concrete tanks which form the support for the boiler room floor and have a capacity of 1,000,000 gallons of fresh water for the boilers. The fresh water and oil storage provided is sufficient to operate the entire station for 96 hours.
Pumping Station No. 2
The location of this station is at Black Point in Fort Mason and is at the northern end of the distributing system. The equipment is practically the same as in Station No. 1 except that Sterling boilers were used instead of Babcock & Wilcox boilers. Two 20-inch pipes lead from this station, one to the upper zone and one to the lower zone.
The entire system is kept filled with fresh water under a high pressure at all times. In case of a fire the engines, hose wagons, hook and ladder and water tower, all motor driven apparatus, answer the call. The reason for the engines answering the call is due to the fact that the Spring Valley Water Company’s hydrants cover the district more completely than the hydrants of the high pressure fire system, and consequently it is generally found more convenient to make use of these low pressure hydrants and use the engines, than to clear the street for a block or more and use the high pressure hydrant. The hose wagons in use are fitted with monitor batteries, thus eliminating the use of the battery wagon.
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San Francisco’s Auxiliary System
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When a high pressure hydrant is used, a pressure reducing valve is first attached to one of the outlets of the hydrant. This valve is ordinarily set for 120 lbs. pressure, which would give a nozzle pressure of about 90 lbs. for a hose 200 feet in length. One high pressure fire hydrant will give more water under pressure than three of the city’s largest fire engines. This is accomplished by using pressure reducing valves with two outlets from each of the three hydrant outlets, and in two of the hose lines leading therefrom are placed Siamese connections, thus giving 8 hose lines from one hydrant, and with 1 1/4″ diameter nozzles at 100 lbs. nozzle pressure, 2,290 gallons of water per minute can be obtained from the hydrant as against 2,250 gallons per minute from the three fire engines.
In Pumping Station No. 1, one battery of boilers is maintained under steam pressure constantly, and the remaining boilers can be put into operation in 30 minutes. The use of salt water from the pumping stations or the fire boats, however, is to be used only in case of a general conflagration or a severe earthquake, followed by a large number of fires.
In case of a large fire in the lower zone, the lower zone system can be connected directly with the pipes of the upper zone by opening one or more gate valves, giving a pressure in the lower zone of 214 lbs. per square inch, or connection can be made with the Twin Peaks Reservoir in like manner, giving a pressure tit 328 lbs. per square inch in the lower zone. The fire alarm boxes are located on the streets, and enable the officer directing the control of the fire to telegraph directly to the gatemen at the tanks and at the reservoir.
When the water is drawn through the fire service connection A in small quantities (say less than that required for one sprinkler head) it will go through the metered by-pass B as the path will offer less resistance than the clapper C of the alarm valve E, and its quantity will be recorded on the meter D. When the flow through the system increases, however, the resistance in the by-pass will become so great as to force the water through the alarm valve. In that case, the clapper in the alarm valve is raised, thus opening the port G in the small pipe H. An air chamber J is placed on this pipe to care for water hammer and to serve as a retarding chamber to prevent false alarms. The pipe H then connects to a recording pressure gauge K. A vent pipe L with a cock M kept partly closed, relieves the pressure in pipe H when the clapper on the alarm valve returns to iis seat. The recording gauge thus registers the time the water is flowing through the alarm valve. A small pipe N leads from pipe H, connecting same with a circuit closer or water motor. On water rising in pipe N, the circuit closer or water motor is operated, thus sounding the fire alarm.
As before stated, there are four sections of the system built on filled ground, with one open valve leading into each section. In case of a severe earthquake, it is proposed to close these open valves, and should a fire occur in the district, the fire engines, by means of the fire cisterns, will endeavor to keep it in check. This is assuming that the domestic water supply system is out of service. As fast as fires in other parts of the city are extinguished, the firemen released from duty from those fires will turn their attention to the filled-in district, and will lead long lines of hose from the hydrants on the adjacent firm ground and from the fire boats on the waterfront, for the purpose of extinguishing the fires in these districts.
Installation of water service expressly for the purpose of affording fire protection is to be made at Camp Sherman, Circleville, Ohio. The improvements will include the laying of additional mains and the erection of standpipes with water pressure of 90 pounds at every building.