(3)
 The servo section includes:

 -
a servo housing assembly,

 -
a pressure regulator,

 -
a pressure relief valve,

 -an electromagnetic control valve,
 -a servo valve. The servo housing assembly is installed on the side of the actuator housing. Air passages inside the housing go between the components of the servo section that are mounted on the housing. A supply-pressure port and a regulated-pressure port are both located in the servo housing assembly. The pressure regulator is made up of a cover, a diaphragm and a poppet. The cover is installed on the servo housing assembly and has a mounting for the diaphragm and the diaphragm spring. The poppet is installed in the supply-pressure inlet port. The spring-loaded diaphragm holds the poppet in the normally open position. The pressure regulator has a chamber that is orifice-ported to the supply-pressure inlet. The Pressure Relief Valve (PRV) is made up of a housing and a ball valve that is spring-loaded closed. The inlet of the PRV is ported to the regulated pressure and the outlet is ported to ambient. The electromagnetic control valve is installed on the top of the servo housing assembly. It includes a torque motor, a flapper, two nozzles (supply and vent) and a port to the servo valve. The torque motor operates the flapper between the two nozzles in a pressure  chamber (chamber B). Chamber B is ported to chamber C of the servo valve. The servo valve has a cover, a diaphragm, a rod, a lever assembly, an extension spring, a valve lever and a control nozzle. The cover and diaphragm form a chamber (chamber C), which is ported to regulated pressure from chamber B of the electromagnetic control valve. The diaphragm is spring-loaded on both sides. The valve lever and the extension spring mechanically connect the diaphragm to the butterfly actuation linkage in the pneumatic actuator. The spring loaded valve lever is attached to the rod at one end; at the other end it is mounted adjacent to the control outlet-nozzle end. It acts as a flow gate across the nozzle which is pneumatically connected to regulated pressure through a control orifice.

 (4) The quick-dump element is installed on the actuator cover and has:
 -
a diaphragm cover,

 -
a spring-loaded diaphragm,

 -
a diaphragm retaining plate,

 -
a diaphragm backing plate. The diaphragm divides the quick-dump element into two chambers, an ambient vented chamber and an air pressure chamber (chamber F). Chamber F is ported to controlled pressure and to chamber E of the pneumatic actuator. The diaphragm and both plates have centered-bores which act as orificed passages between the two chambers (F and E). The diaphragm retaining plate is installed in a fixed position. It acts as a seat for the diaphragm backing plate which is attached to and moves with the diaphragm.

 B. Load Control Valve (Ref. Fig. 001) The load control valve has:
 -a valve flow section,
 -two position indicator switches and a visual position indicator,
 -
a pneumatic actuator and an actuator cover,

 -
a solenoid valve assembly.

 (1)
 The valve flow section is made up of a valve body, a butterfly shaft and a butterfly plate. The valve body is a cylindrical air-flow duct, flanged at each end, for in-line installation with the air ducts. Flanges at the top and bottom of the valve body each have an axially-aligned bore for the butterfly shaft. The butterfly shaft is bearing mounted vertically across the valve body and extends upward through the top of the actuator. The butterfly plate (attached to the butterfly shaft) operates as a spring-loaded air-flow flap inside the valve body.

 (2)
 The position-indicator switch assembly (installed on top of the pneumatic actuator) has:

 -a switch lever,
 -two switches,
 -an electrical receptacle,
 -a switch cover. The switch lever (attached to the end of the shaft) is attached so that rotation of the shaft causes an equivalent rotation of the switch lever. The switch lever makes the switches send an open/closed signal when the butterfly plate is fully open/closed. Visual indication of the position of the butterfly plate is given on top of the switch cover. A groove in the end of the butterfly shaft aligns with an OPEN/CLOSED indicator mark to do this.

 (3)
 The pneumatic actuator is installed on top of the valve flow section and has:

 -an actuator housing,
 -
a cover,

 -
a diaphragm,

 -
a diaphragm retainer and backing plate,

 -
a spring,

 -
a linkage. The actuator housing is installed on the valve flow section at one end. The other end has a flange for installation of the cover. The outer edge of the diaphragm is installed between the flange of the actuator housing and cover. The diaphragm is installed between the diaphragm retainer and backing plate, and is spring loaded in the butterfly-closed direction. The butterfly actuation linkage connects the center of the diaphragm retainer to the butterfly shaft. Movement of the diaphragm retainer causes an equivalent movement of the butterfly valve. The diaphragm and the actuator cover form an air pressure chamber (chamber G). This is ported to regulated pressure through the solenoid valve assembly. A test port (installed next to the electrical connector of the solenoid valve assembly) is pneumatically connected in line between the pneumatic actuator and the solenoid valve.
　
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