Copyright Goodheart-Willcox Co., Inc. Chapter 16 Conditioning and Distribution of Compressed Air 411 The venting orifi ce functions only when the maxi- mum desired operating pressure has been reached in the workstation lines and the regulator poppet valve is completely closed. This means the control spring and the diaphragm force are balanced. Any increase in outlet port pressure then generates additional force on the control-chamber side of the diaphragm and further compresses the control spring. The resulting diaphragm movement opens the venting orifi ce. Air is allowed to escape to the atmosphere, preventing any pressure increase above the maximum regulator setting. This regulator design acts much like a small relief valve to prevent the system from exceeding the pres- sure setting of the regulator. However, the design should not be used as the primary relief valve in a com- pressed air system. Balanced-poppet valve regulators The direct-operated, diaphragm-chamber, and reliev- ing-type regulators use unbalanced poppet valves. Basi- cally, this means that the air pressures on the ends of the poppet are different. Typically, the end of the poppet fac- ing the inlet port is subjected to atmospheric pressure. Basic, diaphragm-chamber regulators Figure 16-19 shows the internal structure of a diaphragm- chamber regulator. This regulator incorporates a separate diaphragm chamber to provide more accurate control of system pressure. The diaphragm-control chamber sepa- rates the regulator side of the diaphragm from direct con- tact with air in the outlet port. This control chamber senses the pressure in the outlet port through a small-diameter sensing orifi ce. The other construction features of this unit are very similar to the direct-operated regulator. Setting the desired system pressure for this regulator design is much the same as for the direct-acting unit. Air from the outlet port must pass through the sensing orifi ce to keep the pressure in the diaphragm- control chamber balanced with the pressure in the out- let port. When the pressure in the outlet port begins to increase, additional air is metered through the sensing orifi ce to keep the pressure balanced. This increased pressure applies greater force on the diaphragm to overcome the force produced by the control spring. The resulting diaphragm movement allows the pop- pet valve to adjust position in the same way as in the direct-operated design. The area of the diaphragm in a diaphragm-chamber regulator is typically much larger than in an equivalent direct-operated unit. The larger diaphragm produces more accurate regulator performance. Relieving-type regulators In the direct-operated and diaphragm-chamber regu- lators, external forces acting on the outlet side of the regulator may increase pressure above the regulator setting. Situations that can cause the pressure to exceed the regulator setting are: • Heating of the system from an external source, such as exposure to direct sunlight. • Unexpected load increases on actuators that move internal elements, turning the actuator into a pump. • Leakage of the regulator valve, allowing system pressure to increase to the pressure level in the distribution line. Figure 16-20 shows the internal structure of a relieving-type regulator. The relieving feature elimi- nates this pressure increase. Overall, the construction of a relieving-type regu- lator is very similar to the basic, diaphragm-chamber design. The primary difference is a venting orifi ce located in the center of the diaphragm. The end of the transfer pin keeps the orifi ce closed while outlet port pressure remains below the maximum setting of the regulator. However, the orifi ce allows the diaphragm- control chamber to be vented to the atmosphere if the pressure in the outlet port exceeds the pressure setting of the regulator. Knob Adjusting screw Adjusting nut Control spring Diaphragm Valve pin Poppet valve Poppet valve spring Bottom plug Venting orifice Spring rest IMI Norgren, Inc. Figure 16-20. A relieving-type pressure regulator uses a venting orifice located in the center of the diaphragm to prevent excessive pressure buildup in the regulator outlet port.