begins to close. This restricts the flow through the ejector strainer assembly. When this flow is restricted, the ejector strainer assembly loses its suction and the inlet pressure is diverted, by way of the suction line, to the main valve cover chamber. The resultant increase in pressure in the main valve cover chamber, as applied to its diaphragm, is sufficient to begin closing the main valve. The main valve disk will move toward its seat until the main valve is passing just enough fuel to maintain pressure that will balance the setting of the pilot valve through the throat of the venturi. Any later change in fuel demand will cause a change in venturi throat pressure. Even the slightest change is enough to cause the pilot valve and the main valve to assume new positions to supply the new demand. This will happen regardless of whether the demand is for a greater or lesser amount of fuel. TOPSIDE INCREASE OF FLOW DE- MAND. —An increase in the rate of flow will first cause a momentary decrease in venturi throat pressure. This decrease in pressure will allow the pilot valve to open wider, which, in turn, increases the flow rate through the ejector strainer assembly. An increase in the ejector strainer assembly flow rate will increase the suction lift of the ejector. The increase of the suction lift is applied to the main valve cover chamber and allows the main valve to open wider. The main valve will open in proportion to the increase of flow demand topside. The main valve will continue to open until the venturi throat pressure builds up to a point where it again balances the setting of the pilot valve spring. TOPSIDE DECREASE OF FLOW DE- MAND. —A decrease in flow rate will cause a momen- tary increase in venturi throat pressure. This increase in pressure will cause the pilot valve to close somewhat, restricting the flow through the ejector strainer assem- bly. A decrease in flow through the ejector strainer assembly will decrease the suction lift of the ejector. This decrease of ejector suction lift will cause an in- crease of pressure in the main valve cover chamber and result in partial closing of the main valve. The main valve will close in proportion to the decrease of flow demand topside. The main valve will continue to close until the venturi throat pressure drops to a point where it again balances the setting of the pilot valve spring. SUDDEN DEMAND DECREASE. —Any sud- den decrease in flow rate will create a sudden, high increase in venturi throat pressure. This sudden in- crease of pressure will be applied to the underside of the diaphragm of the pilot valve to close the main valve in the normal manner. Because of the small size of the orifice in the ejector strainer assembly (1/16- inch diameter), the main valve will close slowly. Ven- turi throat pressure will, at the same time, be applied to the underside of the diaphragm of the control valve to open the control valve. When the control valve opens, full pump discharge pressure is applied to the main valve cover chamber to quickly close the main valve. This quick closing of the main valve reduces the pressure in the distribution riser. The main valve remains closed until the pressure on the discharge side of the main valve drops below the spring setting of the pilot valve. The pressure and fuel that are trapped between the discharge side of the main valve and the discharge side of the venturi, caused by a sudden buildup of discharge pressure, are relieved through the venturⁱ recirculating line back to the draw-off tank. Adjustment and Settings The pilot valve pressure adjustment is made by turning the adjusting screw to vary spring compres- sion on the diaphragm. The control valve adjustment is made by turning the adjusting screw clockwise to increase the pressure. The procedure for adjusting the pressure setting follow: NOTE The following procedure should be carried out after reinstallation of the regulating valve and pilot assembly and after the maintenance check has been performed. The typical desired delivery pressure is 22 psi at the throat of the venturi. 1. Close the control valve by turning the adjusting screw clockwise. 2. Set the pilot valve at 34 psi when fuel is flowing through the main valve at 50 gpm or more. 3. Reduce the pressure setting of the control valve (by turning the adjusting screw counterclockwise) until delivery pressure drops to 32 psi at the throat of the venturi. 4. Tighten the control valve locknut. 5. Reset the pilot valve at 22 psi. 6-14