Aircraft technical Basics: TM 1-413, Aircraft Instruments, 1942: 10. Engine Gage Units

TM 1-413, TECHNICAL MANUAL,  AIRCRAFT INSTRUMENTS, Prepared under direction of the Chief of the Air Corps, WAR DEPARTMENT, WASHINGTON February 2, 1942. (This manual supersedes TM 1-413, November 7, 1940)

SECTION X. - ENGINE GAGE UNITS

41. Purpose and use.-This instrument is a combination of a fuel gage, an oil pressure gage, and an oil thermometer in one standard 2 3/4-inch instrument case under one cover glass. This consolidation reduces the amount of frontal space required for installation on the instrument panel and permits convenient association of these measurements which are so closely related. The specific uses of this instrument are the same as those given for individual instruments.

42. Description.-a. The engine gage unit (fig. 14) consists of three Bourdon tube mechanisms which measure fuel pressure from 0 to 10 pounds per square inch, oil pressures from 0 to 200 pounds per square inch, and oil temperatures from 0° to 100° C. Each of the three units is separate in its function and operation but all three are contained in a single three-piece case and all pointers and scales are placed on a standard instrument dial.

b. The thermometer unit is of the standard vapor pressure type using a progressively restrained Bourdon tube mechanism. It is made with various length capillary tubes ranging from 5 to 28 feet. The instrument case has a raintight seal only, so that atmospheric pressure is always present on the outside surfaces of the measuring elements. Tube nipples are located on the back of the instrument for line connections to the fuel and oil systems of the engine. The markings "Fuel" and "Oil" are molded in the case beside each nipple for identification when connections are made. The instrument is provided with an individual 3-volt light with the receptacle molded as an integral part of the instrument case.

43. Operation.-Operation of the units of this gage are the same as for the fuel and oil pressure gages and the oil thermometer.

44. Installation.-When connecting the units of this gage to the engine, be sure to attach the oil pressure line and the fuel line to their respective connections marked "Oil" and "Fuel" on the back of the instrument case, otherwise serious damage to the mechanisms will result when the engine is started. General information for the installation of this gage is given in section III.

45. Maintenance.-If any one of the three units of this gage becomes inoperative, it is necessary to remove and replace the entire assembly. Maintenance procedure for the units in this gage is the same as that described for individual gages.

(1) Front view.   (2) Rear view.
FIGURE 14.-Engine gage unit.