Chapter IV: The Selection of an Acetylene Generator (2)

In charging the generating chambers of water-feed machines clean all residuum carefully from the containers and remove it at once from the building. Separate from the mass any unslacked carbide remaining and return it to the containers, adding now carbide as required. Be careful never to fill the containers over the specified mark, as it is important to allow for the swelling of the carbide when it comes in contact with water. The proper action and economy of the machine are dependent on the arrangement and amount of carbide placed in the generator. Carefully guard against the escape of gas.

Whenever recharging with carbide always replenish the water-supply.

Never deposit residuum or exhausted material from water-feed machines in sewer-pipes or near inflammable material.

Always keep water-tanks and water-seals filled with clean water.

Never test the generator or piping for leaks with a flame, and never apply flame to an outlet from which the burner has been removed.

Never use a lighted match, lamp, candle, lantern or any open light near the machine.

Failure to observe the above cautions is as liable to endanger life as property.

9. OUTSIDE GENERATOR HOUSES.--(_a_) Outside generator houses should not be located within 5 feet of any opening into, nor shall they open toward any adjacent building, and must be kept under lock and key.

(_b_) The dimensions must be no greater than the apparatus requires to allow convenient room for recharging and inspection of parts. The floor must be at least 12 inches above grade and the entire structure thoroughly weather-proof.

(_c_) Generator houses must be thoroughly ventilated, and any artificial heating necessary to prevent freezing shall be done by steam or hot-water systems.

(_d_) Generator houses must not be used for the storage of calcium carbide except in accordance with the rules relating to that subject (_vide_ Chapter II.).

_Class B.--Stationary Non-Automatic Apparatus_.

10. FOUNDATIONS.--(_a_) Must be of brick, stone or concrete.

(_b_) Must be so arranged that the machine will be level and so that strain will not be brought upon the connexions.

11. GAS-HOUSES.--(_a_) Must be constructed entirely of non- combustible material and must not be lighted by any system of illumination involving open flames.

(_b_) Must be heated, where artificial heating is necessary to prevent freezing, by steam or hot-water systems, the heater to be located in a separate building, and no open flames to be permitted within generator enclosures.

(_c_) Must be kept closed and locked excepting during daylight hours.

(_d_) Must be provided with a permanent and effective system of ventilation which will be operative at all times, regardless of the periods of operation of the plant.

12. ESCAPE-PIPES.--Each generator must be provided with a vent-pipe of ample size, substantially installed, without traps. It must be carried to a suitable point outside the building and terminate in an approved hood located at least 12 feet above ground and remote from windows.

The hood must be constructed in such a manner that it cannot be obstructed by rain, snow, ice, insects or birds.

13. CARE AND MAINTENANCE.--All charging and cleaning of apparatus, generation of gas and execution of repairs must be done during daylight hours only, and generators must not be manipulated or in any way tampered with in the presence of artificial light.

This will require gasholders of a capacity sufficient to supply all lights installed for the maximum lighting period, without the necessity of generation of gas at night or by artificial light.

In the operation of generators of the carbide-feed type it is important that only a limited amount of carbide be fed into a given body of water. An allowance of at least one gallon of generating water per pound of carbide must be made in every case, and when this limit has been reached the generator should be drained and flushed, and clean water introduced. These precautions are necessary to avoid over-heating during generation and accumulation of hard deposits of residuum in the generating chamber.

(Rule 14, referring to the storage of carbide, has been quoted in Chapter II. (page 19)).

RULES FOR THE CONSTRUCTION OF GENERATORS.

The following Rules are intended to provide only against the more hazardous defects usually noted in apparatus of this kind. The Rules do not cover all details of construction nor the proper proportioning of parts, and devices which comply with these requirements alone are not necessarily suitable for listing as permissible for use. These points are often only developed in the examination required before permission is given for installation.

_Class A.--Stationary Apparatus for Isolated Installations._

15. GENERAL RULES. GENERATORS.--(_a_) Must be made of iron or steel, and in a manner and of material to insure stability and durability.

(_b_) Must be automatically regulated and uniform in their action, producing gas only as immediate consumption demands, and so designed that gas is generated without producing sufficient heat to cause yellow discoloration of residuum (which will occur at about 500° F.) or abnormal pressure at any stage of the process when using carbide of any degree of fineness.

The presence of excessive heat tends to change the chemical character of the gas and may even cause its ignition, while in machines of the carbide-feed type, finely divided carbide will produce excessive pressure unless provision is made to guard against it.

(_c_) Must be so arranged that during recharging, back flow of gas from the gasholder will be automatically prevented, or so arranged that it will be impossible to charge the apparatus without first closing the supply-pipe to the gasholder, and to the other generating chambers if several are used.

This is intended to prevent the dangerous escape of gas.

(_d_) The water or carbide supply to the generating chamber must be so arranged that gas will be generated long enough in advance of the exhaustion of the supply already in the gasholder to allow the using of all lights without exhausting such supply.

This provides for the continuous working of the apparatus under all conditions of water-feed and carbide charge, and it obviates the extinction of lights through intermittent action of the machine.

(_e_) No valves or pet-cocks opening into the room from the gas- holding part or parts, the draining of which will allow an escape of gas, are permitted, and condensation from all parts of the apparatus must be automatically removed without the use of valves or mechanical working parts.

Such valves and pet-cocks are not essential; their presence increases the possibility of leakage. The automatic removal of condensation from the apparatus is essential to the safe working of the machine.

U-traps opening into the room from the gas-holding parts must not be used for removal of condensation. All sealed drip connexions must be so arranged as to discharge gas to the blow-off when blown out, and the seals must be self-restoring upon relief of abnormal pressure.

(_f_) The apparatus must be capable of withstanding fire from outside causes.

Sheet-metal joints must be double-seamed or riveted and thoroughly sweated with solder. Pipes must be attached to sheet-metal with lock-nuts or riveted flanges.

This prohibits the use of wood or of joints relying entirely upon solder.

(_g_) Gauge glasses, the breakage of which would allow the escape of gas, must not be used.

(_h_) The use of mercury seals is prohibited.

Mercury has been found unreliable as a seal in acetylene apparatus.(_i_) Combustible oils must not be used in connexion with the apparatus.

(_j_) The construction must be such that liquid seals shall not become thickened by the deposit of lime or other foreign matter.

(_k_) The apparatus must be constructed so that accidental siphoning of water will be impossible.

(_l_) Flexible tubing, swing joints, unions, springs, mechanical check-valves, chains, pulleys, stuffing-boxes and lead or fusible piping must not be used on acetylene apparatus except where failure of such parts will not vitally affect the working or safety of the machine.

Floats must not be used excepting in cases where failure will result only in rendering the machine inoperative.

(_m_) Every machine must be plainly marked with the maximum number of lights it is designed to supply, the amount of carbide necessary for a single charge, the manufacturer's name and the name of the machine.

16. GENERATING CHAMBERS.--(_a_) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness for capacities up to and including 20 gallons, not less than No. 22 U.S. Standard gauge for capacities between 20 and 75 gallons, and not less than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.

(_b_) Must each be connected with the gasholder in such a manner that they will, at all times, give open connexion either to the gasholder or to the blow-off pipe to the outer air.

This prevents dangerous pressure within or the escape of gas from the generating chamber.

(_c_) Must be so constructed that not more than 5 pounds of carbide can be acted upon at once, in machines which apply water in small quantities to the carbide.

This tends to reduce the danger of overheating and excessive after- generation by providing for division of the carbide charges in machines of this type.

(_d_) Must be provided with covers having secure fastenings to hold them properly in place and those relying on a water-seal must be submerged in at least 12 inches of water. Water-seal chambers for covers depending on a water-seal must be 1-1/2 inches wide and 15 inches deep, excepting those depending upon the filling of the seal chambers for the generation of gas, where 9 inches will be sufficient.

(_e_) Must be so designed that the residuum will not clog or affect the working of the machine and can conveniently be handled and removed.

(_f_) Must be provided with suitable vent connexions to the blow-off pipe so that residuum may be removed and the generating water replaced without causing siphoning or introducing air to the gasholder upon recharging.

This applies to machines of the carbide-feed type.

(_g_) Feed mechanism for machines of the carbide-feed type must be so designed that the direct fall of carbide from the carbide holder into the water of the generator is prevented at all positions of the feed mechanisms; or, when actuated by the rise and fall of a gas-bell, must be so arranged that the feed-valve will not remain open after the landing of the bell, and so that the feed valve remains inoperative as long as the filling opening on the carbide hopper remains open. Feed mechanisms must always be far enough above the water-level to prevent clogging from the accumulation of damp lime. For this purpose the distance should be not less than 10 inches.

17. CARBIDE CHAMBERS.--(_a_) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness for capacities up to and including 50 pounds and not less than No. 22 U.S. Standard gauge for capacities in excess of 50 pounds.

(_b_) Must have sufficient carbide capacity to supply the full number of burners continuously and automatically during the maximum lighting period.

This rule removes the necessity of recharging or attending to the machine at improper hours. Burners almost invariably require more than their rated consumption of gas, and carbide is not of staple purity, and there should therefore be an assurance of sufficient quantity to last as long as light is needed. Another important consideration is that in some establishments burners are called upon for a much longer period of lighting than in others, requiring a generator of greater gas-producing capacity. Machines having several generating chambers must automatically begin generation in each upon exhaustion of the preceding chamber.

(_c_) Must be arranged so that the carbide holders or charges may be easily and entirely removed in case of necessity.

18. GASHOLDERS.--(_a_) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness for capacities up to and including 20 gallons, not less than No. 22 U.S. Standard gauge for capacities between 20 and 75 gallons, and not less than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.

Gas-bells, if used, may be two gauges lighter than holders.

Condensation chambers, if placed under holders, to be of same gauge as holders.

(_b_) Must be of sufficient capacity to contain all gas generated after all lights have been extinguished.

If the holder is too small and blows off frequently after the lights are extinguished there is a waste of gas. This may suggest improper working of the apparatus and encourage tampering.

(_c_) Must, when constructed on the gasometer principle, be so arranged that when the gas-bell is filled to its maximum with gas at normal pressure its lip or lower edge will extend at least 9 inches below the inner water-level.

(_d_) Must, when constructed on the gasometer principle, have the dimensions of the tank portion so related to those of the bell that a pressure of at least 11 inches will be necessary before gas can be forced from the holder.

(_e_) The bell portion of a gasholder constructed on the gasometer principle must be provided with a substantial guide to its upward movement, preferably in the centre of the holder, carrying a stop acting to chock the bell 1 inch above the normal blow-off point.

This tends to insure the proper action of the bell and decreases the liability of escaping gas.

(_f_) A space of at least three-quarters of an inch must be allowed between the sides of the tank and the bell.

(_g_) All water-seals must be so arranged that the water-level may be readily seen and maintained.

19. WATER-SUPPLY.--(_a_) The supply of water to the generator for generating purposes must not be taken from the water-seal of any gasholder constructed on the gasometer principle, unless the feed mechanism is so arranged that the water-seals provided for in Rules 18, (_c_), (_d_), and (_e_) may be retained under all conditions. This provides for the proper level of water in the gasholder.

(_b_) In cases where machines of the carbide-feed type are supplied with water from city water-mains or house-pipes, the pipe connexion must discharge into the regularly provided filling trap on the generator and not through a separate continuous connexion leading into the generating chamber.

This is to prevent the expulsion of explosive mixtures through the filling trap in refilling.

20. RELIEFS OR SAFETY BLOW-OFFS.--(_a_) Must in all cases be provided, and must afford free vent to the outer air for any over- production of gas, and also afford relief in case of abnormal pressure in the machine.

Both the above-mentioned vents may be connected, with the same escape- pipe.

(_b_) Must be of at least 3/4-inch internal diameter and be provided with suitable means for connecting to the pipe loading outside of the building.

(_c_) Must be constructed without valves or other mechanical working parts.

(_d_) Apparatus requiring pressure regulators must be provided with an additional approved safety blow-off attachment located between the pressure regulator and the service-pipes and discharging to the outer air.

This is intended to prevent the possibility of undue pressure in the service-pipes due to failure of the pressure regulator.

21. PRESSURES.--(_a_) The working pressure at the generator must not vary more than ten-tenths (1) inch water column under all conditions of carbide charge and feed, and between the limits of no load and 50 per cent. overload.

(_b_) Apparatus not requiring pressure regulators must be so arranged that the gas pressure cannot exceed sixty-tenths (6) inches water column.

This requires the use of the pressure relief provided for in Rule No. 20 (_a_).

(_c_) Apparatus requiring pressure regulators must be so arranged that the gas pressure cannot exceed three pounds to the square inch.

The pressure limit of 3 pounds is taken since that is the pressure corresponding to a water column about 6 feet high, which is about, the limit in point of convenience for water-sealed reliefs.

22. AIR MIXTURES.--Generators must be so arranged as to contain the minimum amount of air when first started or recharged, and no device or attachment facilitating or permitting mixture of air with the gas prior to consumption, except at the burners, shall be allowed.

Owing to the explosive properties of acetylene mixed with air, machines must be so designed that such mixtures are impossible.

23. PURIFIERS.--(_a_) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness.

(_b_) Where installed, purifiers must conform to the general rules for the construction of other acetylene apparatus and allow the free passage of gas.

(_c_) Purifiers must contain no carbide for drying purposes.

(_d_) Purifiers must be located inside of gasholders, or, where necessarily outside, must have no hand-holes which can be opened without first shutting off the gas-supply.

24. PRESSURE REGULATORS.--(_a_) Must conform to the rules for the construction of other acetylene apparatus so far as they apply and must not be subject to sticking or clogging.

(_b_) Must be capable of maintaining a uniform pressure, not varying more than four-tenths inch water column, at any load within their rating.

(_c_) Must be installed between valves in such a manner as to facilitate inspection and repairs.

_Class B.--Stationary Apparatus for Central Station Service._

Generators of over 300 lights capacity for central station service are not required to be automatic in operation. Generators of less than 300 lights capacity must be automatic in operation and must comply in every respect with the requirements of Class A.

25. GENERAL RULES. GENERATORS.--(_a_) Must be substantially constructed of iron or steel and be protected against depreciation by an effective and durable preventive of corrosion.

Galvanising is strongly recommended as a protection against oxidation, and it may to advantage be reinforced by a thorough coating of asphaltum or similar material.

(_b_) Must contain no copper or alloy of copper in contact with acetylene, excepting in valves.

(_c_) Must be so arranged that generation will take place without overheating; temperatures in excess of 500° F. to be considered excessive.

(_d_) Must be provided with means for automatic removal of condensation from gas passages.

(_e_) Must be provided with suitable protection against freezing of any water contained in the apparatus.

No salt or other corrosive chemical is permissible as a protection against freezing.

(_f_) Must in general comply with the requirements governing the construction of apparatus for isolated installations so far as they are applicable.

(_g_) Must be so arranged as to insure correct procedure in recharging and cleaning.

(_h_) Generators of the carbide-feed type must be provided with some form of approved measuring device to enable the attendant to determine when the maximum allowable quantity of carbide has been fed into the generating chamber.

In the operation of generators of this type an allowance of at least 1 gallon of clean generating water per pound of carbide should be made, and the generator should be cleaned after slaking of every full charge. Where lump carbide is used the lumps may become embedded in the residuum, if the latter is allowed to accumulate at the bottom of the generating chamber, causing overheating from slow and restricted generation, and rendering the mass more liable to form a hard deposit and bring severe stresses upon the walls of the generator by slow expansion.

26. GENERATING CHAMBERS.--(_a_) Must each be connected with the gasholder in such a manner that they will, at all times, give open connexion either to the gasholder or to the blow-off pipe into the outer air.

(_b_) Must be so arranged as to guard against appreciable escape of gas to the room at any time during the introduction of the charges.

(_c_) Must be so designed that the residuum will not clog or affect the operation of the machine and can conveniently be handled and removed.

(_d_) Must be so arranged that during the process of cleaning and recharging the back-flow of gas from the gasholder or other generating chambers will be automatically prevented.

27. GASHOLDERS.--(_a_) Must be of sufficient capacity to contain at least 4 cubic feet of gas per 1/2-foot burner of the rating. This is to provide for the requisite lighting period without the necessity of making gas at night, allowance being made for the enlargement of burners caused by the use of cleaners.

(_b_) Must be provided with suitable guides to direct the movement of the bell throughout its entire travel.

28. PRESSURE RELIEFS.--Must in all cases be provided, and must be so arranged as to prevent pressure in excess of 100-tenths (10) inches water column in the mains.

29. PRESSURES.--Gasholders must be adjusted to maintain a pressure of approximately 25-tenths (2.5) inches water column in the mains.