_b._ Fuel troubles at low (1) At temperatures below minus temperature. 20 degrees Fahrenheit, ignition of any standard fuel is uncertain. Operation at these temperatures should be avoided unless tests of fuels by firing with flame throwers are first made. (2) At temperatures above minus 20 degrees Fahrenheit, no difficulty should be experienced with thickened gasoline. When blended fuels are used, the ratio of gasoline content should be increased as temperature decreases. _c._ Failure of ignition See Paragraph 63. cylinder. Section XVI TANK GROUP 65. GENERAL. The tank group stores fuel and pressure. The fuel is placed under pressure when the pressure-tank valve is opened. The tank group is supported upon the firer’s back and shoulders by the carrier. 66. PRESSURE TANK AND VALVE ASSEMBLY. _a. Description and functioning._ The pressure tank and valve assembly (Fig 33) includes: (1) _Pressure tank._ The pressure tank is a lightweight, airplane-type cylinder, able to withstand the great pressure which it contains. The tank is charged with air or nitrogen at 1,700 to 2,100 pounds per square inch pressure by use of auxiliary equipment as described in Paragraphs 31 and 32. This pressure stays in the pressure tank until the weapon is ready to be fired. Opening of the pressure-tank valve releases air or nitrogen through the pressure regulator to the fuel tanks. Oxygen or combustible gases are never used in the tank because a violent explosion may result. The tank is large in capacity to assure ample pressure, and hence full range, for the entire load of fuel. The pressure-tank clamp (Fig 39), a steel-strap device with hinge and toggle-type latch, holds the pressure tank in place on the fuel tanks. (2) _Pressure-tank valve._ (Figs 33 and 34) This valve is screwed into the bottom of the pressure tank. The valve stem slides into the valve end of the valve flexible shaft. When opened by means of the valve handle and valve flexible shaft, the valve permits passage of compressed air or nitrogen through tubes and the pressure regulator to the fuel tanks. The valve is of the quick-opening, packless, diaphragm type.