An electrically actuated canopy pressure seal system is shown in figure 2-11. This type of system is controlled by a pressure regulator and dump valve assembly, which consists of a pressure regulator, a solenoid poppet shutoff and vent valve, and a relief valve.

Electrically Actuated Canopy Pressure Seal Regulator Valve

The canopy pressure seal regulator valve controls the pressurizing and depressurizing of the canopy seal, depending upon the canopy position. The pressure regulator consists of a spring-loaded diaphragm, which controls a poppet valve to admit the correct air pressure to the canopy seal. An adjustment screw is provided at the top of the regulator housing to adjust the output of air pressure. The shutoff and dump valve consists of a solenoid-operated poppet valve, which is spring-loaded to the closed position. When the solenoid is energized (fig. 2-11, view A), the dump valve closes the vent port and opens the regulator shutoff to permit inflation of the canopy seal. The outlet pressure is maintained at approximately 20 psi by the pressure regulator.

When the solenoid is de-energized by the opening of the canopy (fig. 2-11, view B), the dump valve opens the vent port, closes the regulator shutoff to stop the flow of supply air, and dumps the pressure in the canopy seal over-board through the vent line. The relief valve feature of the pressure regulator prevents seal pressure from becoming excessive during rapid altitude changes by venting the seal pressure over-board when the pressure reaches a maximum of 22 psi (fig. 2-11, view C). In case of an electrical failure, the reg-ulator valve is spring-loaded in the dump position.

Ground Test Connections

Most canopy pressure seal systems have ground test connections that are used to ground test the system and to pressurize the system during carrier deck storage. The

Figure 2-12.- Cabin air pressure test panel.

ground test connections (fig. 2-12) are usually located on the cabin air pressure test panel. One connection is used for ground test, and the other, which is normally the seal vent, is used for ground pressurization of the canopy seal.

MAINTENANCE

Maintenance of the canopy system consists of servicing, troubleshooting, and removal and installation of components. The applicable air-craft maintenance instructions manual (MIM) furnishes such information as proper procedure, manpower requirements, materials lists, tool and equipment lists, quality assurance instructions, and maintenance-level instructions for the disposi-tion of defective parts.

Servicing

Servicing is limited to cleaning the canopy seal, ground inflating the canopy seal, and periodic inspections for visible defects, dirt, and foreign material accumulations. All major components of the system are self-sustaining and require no general servicing between overhaul periods for normal operation. When pressurized aircraft are stowed on the carrier flight deck without canopy covers, the canopy seal should be inflated externally to protect the cabin area. Ground pressurization of the canopy seal is accomplished by attaching an external air source to the canopy seal vent and ground pressurization connection (fig. 2-13). Since air pressure applied to this fitting bypasses the system regulator, the air source must be controlled to less than 20 psi to avoid rupturing the seal.

NOTE: Some aircraft are equipped with canopy rain seals that protect the cabin area. In aircraft so equipped, the canopy seal does NOT have to be inflated for the cabin to be protected. Rain seals do not maintain cockpit pressurization.

Troubleshooting

Troubleshooting charts similar to the one in table 2-1 are found in most aircraft MIMs. The troubleshooting chart is provided as an aid in determining the cause, isolation procedure, and remedy for the more common malfunctions within the canopy seal system. When a mal-function is suspected, always ensure that the proper controls have been activated to provide operating potential to the unit to be inspected.

Removal and Installation Procedures

The MIM provides the instructions and visual aids necessary to remove and install the various components of the canopy seal system. In addition to instructions, information such as disposition of defective parts, tools and equipment requirements, and quality assurance instructions is provided. When removing a unit from the air-craft, always ensure that proper measures are taken to prevent the entry of dirt and foreign material into ports and ducts that have been opened to accommodate removal.