(_c_) When 350 pounds is reached, close valve No. 3 tight. [Illustration: Fig 37. Pressure regulator, spring-type.] [Illustration: Fig 38. Pressure regulator, dome-type, showing needle valves and wrenches.] (_d_) Close pressure-tank valve. (_e_) When gage indicates zero, close needle valve No. 1 tight. (11) Open pressure-tank valve and press the fuel valve to observe the pressure with the weapon operating. (12) After final adjustment: (_a_) Close the pressure-tank valve. (_b_) Open the fuel valve and release the pressure from the fuel tanks. (_c_) Remove the pressure gage and plug from the fuel tank. (_d_) Install filling plug. (_e_) Tighten filling plug with wrench. (_f_) If regulator is spring-type, replace its protective cap. 68. FUEL-TANK ASSEMBLY. _a. Description and functioning._ (Figs 4, 5, and 39) The fuel-tank assembly includes: (1) _Fuel tanks._ Two alloy steel fuel tanks hold the fuel before it is propelled to the target. They have a combined capacity, including void, of 4-1/2 gallons. A void of approximately 1/2 gallon is left in tanks when filling to allow for expansion and to permit entry of the compressed nitrogen or air. To speed filling and cleaning of the tanks, two openings are provided on top of the fuel tanks. The openings are threaded to receive the filling-plug assembly and the safety-head plug assembly, which are interchangeable in the openings. Filling operations involve the use of auxiliary equipment and are described in Paragraphs 34 through 40. The carrier and the pressure system are supported on the fuel tanks. [Illustration: Fig 39. Fuel system of tank group and related parts disassembled, showing nomenclature and Chemical Warfare Service stock numbers for requisitioning spare parts.] (2) _Tank connector._ This open passageway between the fuel tanks makes them, in effect, a single container. The location of the tank connector and its large diameter permit easy flow of fuel and pressure between the two tanks. (3) _Hose connector._ The hose connector is the outlet for fuel from the fuel tanks. It is located so that nearly all the fuel is propelled from the weapon if firing positions are correct. (Par 24) One end is welded to an opening in the tank connector. The other end is threaded into the tank coupling. (4) _Frame clamp._ This small metal clamp, with bolt, nut, and washer, holds the hose connector to the carrier frame.