_c. Installation of pressure regulator._ Line up pressure regulator, regulator tube, diffusion-pipe assembly, and fittings carefully so they will not be damaged when threads are tightened. Start threads with the hands. Apply only moderate wrench pressure to complete tightening. Replace carrier or carrier pack if either has been removed. _d. Adjustment of pressure regulator._ The pressure regulator ordinarily requires no attention other than checking and tightening connections with the regulator tube and the diffusion-pipe assembly. If a defect in the regulator is indicated by falling off of the range of the weapon or by frequent breakage of the safety-head diaphragm (Par 56 _b_), the following procedure should be carried out. (When using wrenches, do not apply excessive force.) (1) Remove the filling plug (Par 69 _b_) and ignition cylinder. (Par 30 _a_) (2) Fill the fuel tanks with 4 gallons of water (or fuel). (3) Connect the 0-to 500-pound fuel-tank testing gage, found in the service kit, to the filling-plug hole. Tighten plug of gage with wrench. (4) Charge the pressure tank to a pressure of 1,800 pounds per square inch. (Pars 32 and 33) (5) Open the pressure-tank valve. (6) Read the pressure on the gage. If 350 to 390 pounds is indicated, omit steps (7) through (10). (7) _To increase the pressure of a spring-type regulator_: (_a_) Pry off the protective cap. (_b_) Turn a set-screw wrench clockwise in the adjusting screw and read pressure on gage. (8) _To decrease the pressure of a spring-type regulator_: (_a_) Turn the set-screw wrench counterclockwise more than is considered sufficient to effect the desired reduction. (_b_) Turn the pressure-tank valve off. (_c_) Relieve pressure in the fuel tanks by compressing the fuel valve until the pressure is below that desired. (_d_) Release the fuel valve. (_e_) Open the pressure-tank valve and allow the system to reach a state of equilibrium, which occurs when the hissing sound ceases. (_f_) Repeat the steps described above in (6) and (7). (9) _To increase the pressure of a dome-type regulator_: (_a_) Open needle valve No. 1 one full turn. (Fig 38) (_b_) Open needle valve No. 2 one full turn. (There will be slight leakage around the needle-valve thread.) (_c_) Open needle valve No. 3 very slowly, watching pressure gage closely. (As pressure builds up in fuel tanks there will be slight leakage through needle valve No. 1.) (_d_) When the pressure gage indicates 350 pounds, close needle valve No. 3 tight. (_e_) Close needle valve No. 2 tight. (_f_) Close pressure-tank valve. (_g_) When gage indicates zero, close needle valve No. 1 tight. (10) _To decrease the pressure of a dome-type regulator_: (_a_) Open needle valve No. 1 one full turn. (Fig 38) (_b_) Open needle valve No. 3 very slightly, which will lower the pressure.