NOTE—Readers are invited to send in questions, which will be answered in the order received. Names are omitted from questions unless otherwise specified.

Capacity of Pumper at Different Pressures

We would be very grateful if you would answer the following questions in the Questions and Answers Department of your next issue:

A pumper has a capacity of 700 gallons per minute at 150 pounds pressure. If the pressure is increased to 175 pounds the discharge decreases.

Question 1. If the pressure is decreased to 125 pounds does the discharge increase?

Question 2. What is the greatest pressure that can be had from the above pumper?

Question 3. Give formula for finding answer to question 1. H. W.

Answer 1: Yes, the discharge can be increased it the pressure is reduced.

Answer 2: This question cannot be answered, for it depends entirely upon the power of your motor, the gear arrangement, and the strength of the pump itself.

Pumps are so powered and geared that they will give maximum discharge at various pressures likely to be required in fire service. They are not built just to create pressures alone, for capacity is as important as pressure. As the different types of pumps arc built along different principles, each make of pump would have a different maximum pressure as well as discharge, and in any specific case it could only be determined by tests.

Answer 3: The National Board of Fire Underwriters have suggested the following practical standards on pumping engine capabilities at different pressures: At 120 lbs. engine pressure, full rated capacity; at 200 lbs. engine pressure, one-half rated capacity; at 250 lbs. pressure, one-third rated capacity.

The rule employed in figuring the capacities of pumping engines at different pressures when working fire department promotional examination problems is as follows: Multiply the rated discharge by the rated pressure and divide this product by the pressure at which you wish to find the discharge. As an example, if an engine has a rated discharge of 700 gallons per minute at 120 lbs. pump pressure and you wish to find the discharge at 150 lbs. pressure, you would multiply 700 by 120 and divide the product by 150, giving 560 gallons per minute.

This method, it should be mentioned, does not give accurate results, but is only a theoretical solution for discharge based upon the assumption that the same power is utilized irrespective of the discharge or pressure. Nor does it take into account the question of slippage.

During the past year a law was passed in this state making it compulsory to wash all apples sprayed with arsenate of lead. Muriatic and hydrochloric acids are used in great quantities. I would be very much obliged if you would explain the effects of both acids as regards life and fire. There are large quantities of both acids stored in warehouses and cold storage plants in this city.

Answer: Arsenate of lead has no fire hazard but it is a very poisonous material if taken internally. The fact that it is shipped in wooden barrels is sufficient evidence of the absence of fire hazard.

Muriatic and hydrochloric acids arc the same. They arc technically known as “hydrochloric acid” although the name muriatic is frequently used. Hydrochloric acid is a clear, colorless or slightly yellow, fuming, pungent liquid, and is poisonous if taken internally.

The fumes, like those of chlorine, may do serious damage if inhaled in quantities, but as they are pungent they give sufficient warning of their presence so that the firemen can be on their guard.

While highly corrosive to certain metals, hydrochloric acid constitutes no fire hazard. It is shipped in wooden tank cars or wooden barrels.

What care should be given cotton hose used in school buildings?

Is it better to test out the hose, say once a year, or to keep it dry and forego the tests?

How long is it safe to rely on such hose before replacing?

Answer: As you do not state that the hose is lined, it is assumed that it is unlined and in this case is, in all probability, unlined linen hose, as unlined cotton hose is not used for fire protection purposes.

On this assumption, it is better not to test the hose. Unlined linen hose will last indefinitely if not exposed to the elements and if not subject to abuse. On the other hand, testing of the hose and the consequent saturation of the fabric would tend to shorten its life; also, linen hose when tested and replaced will never hang as evenly as untested hose with a result that tested hose always looks carelessly hung.

As to the life of such hose, when not abused or subjected to test or frequent use, it may be one, two or more decades.

Here’s a precaution which must be observed; In public buildings the couplings, nozzle, and other brass work on the hose are frequently polished to keep them attractive. Polishing pastes employing oxalic acid and other materials destructive to hose fabrics are employed. If the polishing is carelessly done and if some of the paste gets on the hose near the coupling the hose will be materially weakened and the couplings may subsequently blow off when the hose is brought into play.

Should the hose you have in mind be cotton rubber lined hose, it is advisable to test it at least once a year and to run water through the hose about every two months. This operation will tend to keep the rubber in good condition and prevent cracking which would otherwise occur by the rubber lining “aging out.”

I would greatly appreciate an answer to the following problem at your earliest convenience, giving full details, formulas, etc.

An engine at 150 pounds pressure is pumping through two parallel lines of 3-inch hose each 300 feet long to a Siamese connection from which is stretched 200) feet of 2 1/2 inch hose. 50 pounds is desired at the nozzle. What size nozzle should he employed in order to secure 50 pounds nozzle pressure with the above layout and engine pressure as given?

Also, in a recent issue you printed an article where a New York fire officer used water and foam at a fire in the kettle plant of a varnish factory to no avail, but extinguished the fire with a carbon dioxide gas extinguisher. Is it true that foam was used to no avail?

Answer: The first step in this solution is to reduce the two 300 foot lines of hose to a single line of 2 1/2 inch. The factor for reducing parallel 3 inch lines to 2 1/2 inch is 9.35 300 / 9.35 = 32.1 feet of 2 1/2 inch hose. Add this to the 200 foot stretch of 2 1/2 inch hose and we get a total length of 232.1 feet of 2 1/2 inch hose which represents the layout as given in the problem. The problem may then be considered as an engine at 150 pounds pressure pumping through 232.1 feet of 2 1/2 inch hose to a nozzle, the pressure at which is 50 pounds. The problem is to find the size of nozzle.

Employ the Underwriters’ formula. Engine pressure = nozzle pressure x (1.1 + KL).

Put the values we already have into this formula and then solve for the value of K. Engine pressure we know is 150 pounds; nozzle pressure is 50 pounds; L, the number of 50 foot lengths of hose in the line is 4.64.

Solving out, we find K equals 0.41.

Now checking over the values of K for different sizes of nozzles on a single stretch of 2 1/2 inch hose, we find that K for a 1 1/2 inch nozzle is .505 and for a 1 3/8 inch nozzle is .341. The latter figure is the nearest to that we get by our solution and therefore the nozzle we would have to employ to get 50 pounds pressure or thereabouts would have to be 1 3/8 inch in diameter.

Now let us check this up and see what we get by solving for nozzle pressure with a 1 3/8 inch nozzle.

N. P.= E. P. / (1.1 + K x L)

= 56 pounds nozzle pressure, which is near enough to the nozzle pressure desired.

With regard to the second question you ask, the report as furnished to this office was vouched for by the manufacturer of the carbon dioxide gas extinguisher employed. It may be added here that foam extinguishers are ineffective in extinguishing fire in alcohol and carbon disulphide, both of which fluids are commonly employed in manufacture of varnish. It is very likely that one or both were encountered at this fire, if foam did not work satisfactorily. As far as the use of water goes, there is danger in employing water where large quantities of inflammable liquids are afire and where the temperature has reached a high point.