Questions and Answers
NOTE—Readers are invited to send in questions, which will be answered in the order received. Names are omitted from questions unless otherwise specified
A request was published on this page in the March issue, submitted by a reader who sought copies of charters, constitutions and by-laws of volunteer Fire Departments.
Acknowledgment is made to the following who submitted specimens of these documents from their respective organizations: Horace Jacobs, Secretary of the Abington Fire Company. Abington, Pa.; Irving W. Johnson, Chairman of the Publicity Committee of the Takoma Park Volunteer Fire Department, Takoma Park, Md.; and Charles M. Hollis, Jr., President of the Seaford Volunteer Fire Department, Seaford, Del.
Nozzle Pressure and Discharge
To the Editor:
Would you kindly work out the following problems:
- First Layout—Two 100-foot lines of 2 1/2-inch hose into a deluge set with a 2-inch tip, and one 100foot line of 2 1/2-inch hose with a 1 1/8inch tip. The pump pressure is 124 pounds. What is the nozzle pressure ? How many gallons of water per minute?
- Second Layout—One 100-foot line of 2 1/2-inch hose with a 1 5/8-inch tip. The pump pressure is 200 pounds. What is the nozzle pressure ? What is the number of gallons per minute ?
- Third Layout—One 100-foot line of 2 1/2-inch hose with a 1 1/4-inch tip. The pump pressure is 200 pounds. What is the nozzle pressure? What is the number of gallons per minute? M. J. K.
Answer 1 : In problem No. 1, you have an engine at 124 pounds pressure pumping through three lines of 2 1/2-inch hose. Two of the lines are siamesed into a deluge set equipped with two-inch nozzle, and the other line, a single line of 2 1/2-inch hose, is equipped with 1 1/8-inch nozzle.
Nozzle pressure = E.P. (1.1 + K1) where K is a factor depending upon the nozzle and hose diameters. For two parallel lines of 2 1/2-inch hose, siamesed into a deluge set equipped with 2-inch nozzle, the value is .418.
L, the number of 50 foot lengths of hose in the line, from the engine to the nozzle, is 100 / 50 or 2.
Then nozzle pressure = 124 / (1.1 + .418 X 2).
Or nozzle pressure = 124 / 1.936, or 64 pounds.
Discharge = 30 X d X d X √P, where d is the diameter of the nozzle in inches, and p, the pressure in pounds per square inch.
Or discharge = 30 X 2 X 2 X 8.
= 960 g.p.m.
Solving for the single line of hose equipped with 1 1/8-inch nozzle, K for this layout equals .167.
L, the number of 50 foot lengths in the line, equals 2.
Then N.P. = 124 / (1.1 + .167 X 2) = 124/ 1.434, or 86.47 pounds nozzle pressure.
Discharge = 30 X d X d X √p
= 30 X 1 1/8 X 1 1/8 X √86.47
= 30 X 1.125 X 1.125 X 9.3
= 353 g.p.m.
Answer 2: Here we have a single line of 234-inch hose 100 feet long and equipped with 1 5/8-inch nozzle. Engine pressure is 200 pounds.
K, for 2 1/2-inch hose with 1 5/8-inch nozzle = .680.
L. the number of 50 foot lengths of hose in the line = 2.
Then nozzle pressure = 200 / (1.1+ .680 X 2)
= 200 -H 2.46 = 81.3 pounds nozzle pressure.
Discharge = 30 X 1 5/8 X 1 5/8 X √81.3 = 30 X 1.625 X 1-625 X 9.016.
= 714 g.p.m.
Answer 3 : The engine is operating at 259 pounds pressure, and is pumping through 100 feet of 2 1/2-inch hose equipped with 134-inch nozzle.
K, for 1 1/4-inch nozzle on 2 1/2-inch hose, equals .248.
L, the number of 50 foot lengths of hose in the line equals 2.
Then nozzle pressure = 259 / (1.1 + .248 X 2)
= 162 pounds
Discharge = 30 X 1 1/4 X 1 1/4 X√62
= 30 X 1.25 X 125 X 12.72
= 596 g.p.m.
K for Small Nozzles
To the Editor:
Will you he kind enough to tell me what “K” to use on 1/2-inch, 5/8-inch and 3/4-inch tips?
Answer: The values of K for the various sized nozzles you gave, when attached to 2 1/2-inch fire hose, arc as follows:
For 1/2-inch nozzle on 2 1/2-inch hose, .00625.
For 5/8-inch nozzle on 2 1/2-inch hose, .01527.
For 3/4-inch nozzle on 2 1/2-inch hose, .03164.
The last two figures may be dropped from each of these factors without producing any serious inaccuracies.
To find the value of K for any other size of hose than 2 1/2-inch, divide the value of K for a single line of 2 1/2-inch hose, using any nozzle, by the factor of any other line employing the same sized nozzle. For example, if we were to find the value of K for 1/2-inch nozzle on 1 1/2-inch rubber lined hose, we would divide the value of K for 1/2-inch on 2 1/2-inch hose (.00625) by the factor for converting 1 1/2-inch hose to 2 1/2-inch, which is .074, which gives .0845, the value of K for 34-inch nozzle on 1 1/2inch hose.
Explosibility of Oxygen and Oil
To the Editor:
I would like to obtain some information on oxygen. I understand that oil and oxygen, when compressed, will explode. Does this same condition exist under ordinary circumstances? For instance, is it safe to enter an oil storage tank with an oxygen mask? If there was a slight leak in the piping on the mask, would there be a possibility of an explosion ?
E. J. B.
Answer: There should be no danger whatsoever in using an oxygen helmet in an oil tank. The hazard of oxygen and oil is created when a mixture of oil and oxygen is compressed to fairly high pressures. Explosions are apt to occur under these conditions.
The effect is not unlike that produced in a deisel engine, where a mixture of atomized oil and air is compressed to such a temperature as to ignite the mixture. With oxygen, however, combustion (explosion) takes place at a much lower temperature, and therefore a much lower pressure.
Salf for Chimney Fires
To the Editor:
How much value has salt when used to extinguish chimney fires?
A discussion has arisen among those interested in fire lighting in our town, but the firemen still stick to their booster lines and ponies. Are we right?
Answer: If the fire is burning at the base of the chimney, or in the furnace, dampened salt thrown on the fire will cause the generation of hydrochloric acid gas. This has a material effect in smothering the fire, though it is not as effective as some of the chimney fire compounds on the market at the present time. The booster line is highly effeetive for chimney fires, if a spray nozzle is used, with very fine spray, and is lowered down the affected chimney. Salt is not nearly as certain to produce results as is the spray nozzle.