Practical Training for Auxiliary Firemen
Editor, FIRE ENGINEERING
IN this installment of the series of articles on “Practical Training for Auxiliary Firemen” is discussed pump operation and gauges.
Q. What are the three types of gauges commonly found on fire engines?
A. Pressure gauge, vacuum gauge and compound gauge.
Q. What is the purpose of the pressure gauge on the pumper?
A. The pressure gauge gives the pressure in pounds per square inch developed by the pump on a fire engine.
Q. What is the function of the vacuum gauge?
A. The vacuum gauge records the negative pressure, or vacuum, developed on the intake side of a pumper. This vacuum may be produced either by lifting water by suction or drawing from the water system where the flow is inadequate.
Q. What is the function of the compound gauge?
A. The compound gauge records either vacuum or pressure. To the left of the zero on the compound gauge (reading counter-clockwise), the readings are shown in “inches” of vacuum. By inch of vacuum is meant a vacuum represented by the equivalent of an inch of mercury. As one inch of mercury is equivalent to 1.134 feet of water, the reading in inches of vacuum is commonly considered as feet of water. Thus a reading of 10 on the vacuum gauge would be taken to indicate a negative head, or lift, of 10 feet. From zero, measured clockwise, the readings indicate pounds of pressure per square inch.
Q. Are pressure gauges and compound gauges ever calibrated in other than pounds pressure?
A. Occasionally gauges arc calibrated in “feet” of water. Thus a reading of 200 on the pressure gauge would indicate a head of 200 feet of water.
Q. Where are the various types of gauges commonly located on pumpers?
A. Pressure gauges are usually found on the discharge side of all positive displacement pumps.
Vacuum gauges are not often used on fire apparatus, but when employed, are placed on the intake side of the pump.
Compound gauges are installed on the suction side of all pumps and are usually provided in place of the straight pressure gauge on the discharge side of centrifugal pumps. This gauge shows the pressure received from the hydrant, or the vacuum created on the intake side, whichever happens to be the case.
Q. What is the first thinn to do when a pumper is to be placed in service at draft?
A. Select a site as near as possible to the source of supply (i. e. river, lake, creek, etc.) but at the same time making sure that the pumper will be on a firm foundation. Make sure the lift at the site selected is well within the capabilities of the engine.
Q. In the event that the ground alongside the body of water from which draft is to be taken is not firm, what may be done?
A. Place planks, or rocks, at the point pumper is to be placed so as to provide satisfactory foundation.
Q. If a pumper is to be placed on a wooden pier which has not been used recently, what precautions should be taken?
A. Check the planking on the pier as well as supporting beams. If the planking is decayed or apparently weakened, other planks should be placed lengthwise on the pier, and the truck rolled in on these planks. The use of the new planks, laid loosely over present pier flooring, distributes the load and reduces the likelihood of failure of pier planking under the weight of the truck.
Q. Where a pumper has been driven into position to operate from draft at a surface source supply, and is to be placed in operation, what preliminary steps should be taken?
A. First check the brake, and use chocks under wheels to prevent movement of the truck, particularly if the ground is inclined. Before the driver leaves the truck, he should disengage the drive to the wheel axles and engage transmission in proper gear for pumping. Gear shift lever locks should then be engaged to prevent accidental shifting of gears. Throttle is thereupon set to provide an idling speed a little above ordinary speed.
Q. What procedure is followed in connecting up suction hose and getting it in readiness for operation?
A. The first step is to connect up the lengths of suction hose to be used. If the lift requires two lengths, these should be hooked up first; if it requires three lengths, the three sections are hooked up before being connected to the pumper.
After the lengths arc connected up. rope is attached to the eye on the end of the strainer to provide a means of raising or lowering it as desired.
After these connections, etc., have been made, then the other end of the suction line is attached to the intake connection on the pump, and the connection drawn up tight. The pumper is now ready for operation.
Q. How deep should the strainer be submerged under water?
A. The strainer should be placed 1 1/2 feet or more beneath the surface of the water.
Q. Why is it necessary to place the strainer at this depth?
A. To prevent the entrance of air into the suction line. Incidentally, the’ depth referred to above is the depth of the uppermost part of the strainer below the surface of the water. ,
If the strainer is permitted to remain too near the surface, whirlpools are formed, and air enters through these whirlpools into the strainer and from there to the suction line into the pump. This air upon leaving the nozzle on the end of the line will destroy the effectiveness of the stream.
Q. In the event that the depth of water in the source of supply is insufficient to provide proper coverage of the strainer, what steps should be taken to prevent air from entering the strainer?
A. Where the strainer is submerged but a short distance, the formation of whirlpools and the entrance of air into the strainer may be quite effectively checked by placing a wide board or door on the surface ot the water directly over the strainer.
Q. How near the bottom of a stream may a strainer be placed when a hre engine is to pump from drait?
A. This depends upon the nature of the bed of the stream, or other source of supply being used. If the bottom of the stream, or other body of water, is covered with leaves or other debris which might clog the screen, the strainer should not be permitted to approach, the bed of the stream nearer than one foot. The rope attached to the strainer is fastened to some object ashore to keep the strainer at proper level.
Q. If the depth of the water is inadequate to permit a clearance of twelve inches between the strainer and the bed (of the stream, pond, lake, or other source of supply), what precautions should be taken?
A. When the depth of water is inadequate, place plank, door, ladder, sheet metal, etc., between strainer and the bottom to prevent drawing sand, stones, leaves, and other foreign materials into the pump.
Large wire, splint or mesh basket placed over the end of the suction hose is often a valuable auxiliary to the suction strainer, particularly when pumping from water with considerable debris in it. If time permits, a large box or barrel may be embedded in the body of water to increase the effective depth of the end of the suction hose.
Q. After necessary hose layouts are attached to discharge outlets of pump, and the pump is being readied for operation, what precautions should be taken?
A. He sure that all drain valves and other connections are tightly closed; be sure that the blank cap on the suction inlet of the pumper (to which suction hose is not attached) is closed tightly.
Q. What steps are followed when positive displacement type of pump (piston or rotary gear) is placed in operation, particularly insofar as priming the pump is concerned?
A. The first step is to open the discharge gates, to which hose lines are attached, and to close the churn valve.
Pump gear is placed in “capacity” and the throttle opened up, to turn the engine over at a moderate rate of speed.
It is unnecessary to race the engine when priming.
After water has reached the pump, and pump has been primed, then the motor is speeded up to such a point as to give the desired water pressure at the engine.
In the event that lines are long, or that a higher pressure is desired at the pump, the pump control is shifted to “pressure”.
Incidentally, in making such changes from pressure to capacity or capacity to pressure, the throttle is retarded during the operation.
Q. What are the steps to be followed in the priming of a centrifugal type of pump?
A. First, close all discharge valves, and close the churn valve, if such is provided. If pump is of the parallel series type, set the control valve for “capacity” or “pressure” as desired. If the pump is provided with auxiliary rotary priming pump, engage the priming pump and increase speed slightly.
If the pump is provided with auxiliary vacuum priming from the motor (or similar device), engage the centrifugal pump impeller and open the valve in vacuum connection; increase speed very slightly.
When the pump is primed, it will be noticed by the discharge of water from the auxiliary priming pump, or by registration of pressure in the centrifugal pump with vacuum priming. Disengage the priming pump and engage the centrifugal pump impeller simultaneously, or close vacuum control valve.
Increase the speed slowly to maintain adequate pressure in the pump while the discharge valves are being opened. After the valves are opened, advance the throttle until the desired engine pressure is indicated on the gauge.
When the desired pressure is obtained, set the relief valve or governor to operate at a few pounds higher than the desired operating pressures; about five pounds above the normal pressure is usually considered sufficient.
Open the cooling water supply control valve to maintain motor temperature within the range recommended by the manufacturers.
If tachometer is provided, observe motor speed from time to time. Also observe water temperature, oil pressure, fuel and water pressure gauges frequently.
Q. What steps are taken when shutting down the pump after it has been in operation?
A. If the shut-down is to be of short duration, it will not be necessary to disengage the trump gears. Retard the throttle to maintain about twenty-five pounds pressure with the line shut down and with churn valve open. To resume operation, it is only necessary to open the line, close the churn valve and advance the throttle.
For a permanent shut-down, retard the throttle, open churn valve, close discharge valves, disengage pump gears, close auxiliary cooling line, bleed hose line, drain pump and disengage suction and discharge hose.
Q. Where suction is to be taken from hydrant, rather than by draft, what steps are usually followed in placing pumper in operation?
A. First, the pumper is so located as to make easy connection to the hydrant selected. The suction hose is connected to the hydrant and the suction intake on pumper, and precaution is taken to make sure that gaskets are provided and the connections are tight.
Then close the discharge valve on the pumper, and close the churn valve and all drain valves. Make sure that the cap on the suction connection on the other side of the pumper is tight. Open the hydrant wide.
When lines are ready for use. engage the pump gear shift lever in proper position. Open the discharge gate valve, and advance throttle sufficiently to obtain the desired pressure as indicated on the pressure gauge. Observe the. safety precautions as described in the method of operating pumper from draft, insofar as setting the relief valve or governor, opening of cooling water valve and observing gauges and indicators, are concerned.
Q. If the pressure on the suction side of pump, operating at hydrant, shows a serious pressure drop, what does it indicate?
A. It usually indicates that the main tp which hydrant is attached is being asked to supply more water than it is capable of delivering.
Incidentally, if the pressure on the intake side of pumper shows less than five pounds, it is better to reduce the discharge from such a pumper bv shutting down one of the lines or reducing the size of nozzle or nozzles. Under no condition should a pumper be operated at a vacuum when taking suction from a hydrant.
Q. When a fire engine returns to Quarters from a fire, what check-ups are usually recommended?
A. Check the amount and condition of oil in crankcase and add oil, if necessary. If oil is too thin or shows excessive foreign matter, drain off and replace with fresh oil.
Check gasoline tank, and if necessary, fill tank. Check water in radiator and. if necessary, add water.
Check important lubrication points: examine for missing or loose parts and make a report of the same.
Clean entire apparatus and dry thoroughly all parts subject to rust.
Leave apparatus ready for immediate response to next alarm.