Diaphragm-operated fluid flow control valve providing a plurality of flow levels

A fluid control valve having

• a) a valve body;
• b) an inlet chamber for connection to a source of pressurized fluid;
• c) an outlet chamber for connection to a device for dropping fluid pressure to essentially atmospheric;
• d) a main valve seat interposed between the inlet and outlet chambers;
• e) a main valve element;
• f) a main valve diaphragm carrying on a valve side thereof the main valve element in facing and opposed relation to the main valve seat, said valve side of the main valve diaphragm defining a part of one of one only of the inlet and the outlet chambers, and said main valve diaphragm having opposite the valve side a control side defining with the valve body a main valve diaphragm chamber;
• g) a main valve spring applying force to the main valve element to urge the main valve element toward the main valve seat, wherein the force balance arising from pressure in the one only of the inlet and the outlet chambers, the main valve diaphragm chamber pressure, and the main valve spring determines the spacing between main valve element and the main valve seat;
• wherein the improvement comprises:
• h) a first flow restrictor connected between the inlet chamber and the main valve diaphragm chamber;
• i) a second flow restrictor connected between the outlet chamber and the main valve diaphragm chamber, said first and second flow restrictors in combination forming a pressure divider connected between the inlet chamber and the outlet chamber;
• and
• j) a servo valve operable between open and closed states and in flow connection with the main valve diaphragm chamber, and when in a preselected one of the open and closed states enabling the pressure divider to control main valve diaphragm chamber pressure, and when in the other of the open and closed states, enabling one only of the inlet chamber pressure and the outlet chamber pressure to propagate to the main valve diaphragm chamber.