CROOM CALCULATOR ON PUMPER SIMPLIFIES PRESSURE CALCULATIONS
Indicator is Designed for the Three Most Common Nozzle Sizes—Examples of its Application Described
THE Croom Master Gage and indicator, designed and patented by J. Luddie Groom, Chief of the Wilmington, N. C., Fire Department, is a simple pressure indicator for use by fire department pumper operators. It is so arranged that at a glance the operator can determine the necessary pressure to be carried at the pumper to maintain the proper pressure for various sized nozzles and various lengths of hose.
Arranged for Common Nozzles
The indicator is arranged for use with the three most generally used nozzle sizes, 1-inch, 1 1/8-inch and 1 1/4-inch. The four bands or circles are for pressure in pounds per square inch, and for the three size nozzles. Other and larger size nozzle bands could be added if needed. The outer band is calibrated as an ordinary pressure gage. The first inner band is calibrated for a 1-inch nozzle, the next for a 1 1/8-inch nozzle, while the innermost band is for the 1 1/4inch nozzle. The three inner bands are marked in hundreds of feet of hose used in strecth-in, indicating on the circle opposite, the various lengths of hose lines, fhe necessary pressure to be held on the pumper to give the generally used nozzle pressure. In the case illustrated, on page 195 of the May issue, the calibrations are for 45 pounds pressure on oneinch nozzle and 50 pounds pressure on other two size nozzles.
In use the only information necessary for the pumper operator is the length of stretch-in and the size of nozzle. With this information at hand the operator selects the proper band of indices and reads opposite the hose length the necessary pressure for his pumper. For instance, a 1 1/4-inch nozzle with a 500-foot stretch-in will require 178 pounds at the pumper. The operator does not have to make a calculation nor turn a dial. He simply finds the hose length in the proper band, opposite which, in the pressure band, is the required pressure. In fact the outer band could be removed entirely and the pressure indicating band set over the indice indicating the length of stretch-in. In case there are two or more lines of hose from one pumper, the operator selects the one requiring the greater pressure and sets his indicating needle to this pressure. Though the shorter lines will give a greater pressure, the longer line will have the standard pressure at the nozzle.
There is a correction for elevation. The operator determines the pressure necessary for hose length and nozzle size, and adds five pounds for each story of building. With a stretch-in of one thousand feet of hose, and a 1 1/8-inch nozzle used on the fourth floor of the building (the building and hydrant being approximately at same elevation) the operator finds the indice ten on the 1 1/8-inch band, reads his pressure in the outer band, which in this case will be 222 pounds, then adds the necessary fifteen pounds for elevation of nozzle above pumper. This makes the pumper pressure required 237 pounds.
In the illustration used there is a permanent indicator to ze used as standard booster hose pressure, in this case 80 pounds, as it is standard for 3/4-inch booster hose. Of course a greater or lesser pressure can be used for booster hose than indicated, if it is so desired.
In the use of the gauge, it is not necessary for the operator to know anything but the length of stretch-in, the size of nozzle and the elevation above pumper level, if any. The gauge and indicator are integral and always ready for use unless the gauge is removed from the pumper.