Copyright Goodheart-Willcox Co., Inc. 412 Fluid Power The setting of the secondary regulator controls the air pressure in the pilot-air chamber of the primary regulator. During operation, the air pressure in the pilot-air chamber generates a force on the regulator diaphragm. This force is in place of the force produced by the con- trol spring of the basic regulator design. The secondary regulator provides pilot pressure adjustment, which replaces the adjustment screw of the basic regulator. Basically, the pressurized air in the pilot-air chamber acts as an adjustable air spring that establishes the pressure setting of the pilot-operated regulator. The construction and operation of the remainder of the regulator are the same as the basic, diaphragm-chamber regulator. Regulator selection Factors that must be considered when selecting a regu- lator for a system are: • Choice of a direct-operated basic, diaphragm- chamber relieving-type balanced-poppet valve or pilot-operated style, depending on system size and performance demands. • Pressure range of the unit, which considers the pressure in the input distribution line compared to the desired output pressure at the workstation. • Airfl ow range of the unit. • Conductor connection size. Manufacturer information and specifi cation sheets supply these types of detail for the various models produced. The opposite end is subjected to varying, higher system pressures. The difference in these pressures causes operating variations as the regulator compensates for load variations in the workstation lines. Figure 16-21 shows a balanced-poppet valve regulator. Both ends of the poppet are exposed to approximately the same pressure. This produces bal- anced forces acting on the valve. The valve is posi- tioned only by the force generated by the pressure in the diaphragm-control chamber and the poppet spring. The construction of the remainder of this type of valve is primarily the same as the basic, diaphragm- chamber regulator. This design results in reduced fl uctuations in the regulated pressure and improved response during the normal range of operation. The feature is most often found on large-capacity units. Pilot-operated regulators In some installations, the regulator must be located in a remote location to maintain maximum system effi ciency. These remote locations often have limited access, which makes it diffi cult to adjust the pressure of the regulator. In these situations, a pilot mechanism is used to control a primary regulator with a small, secondary regulator located at an easily accessed location. Figure 16-22 shows the structure of a pilot-operated regulator. In a pilot-operated regulator, the diaphragm- control spring and adjustment screw are replaced by a sealed, pilot-air chamber. This chamber is connected to the secondary regulator located at the operator work- station via a small-diameter air line. See Figure 16-23. Outlet port (reduced pressure) Pilot line between poppet valve and outlet port Inlet port (supply pressure) Goodheart-Willcox Publisher Figure 16-21. A balanced-poppet valve regulator uses a design that exposes both ends of the poppet to equal pressure. This increases performance accuracy.