Air Diverter Valve: Description and Operation

There are two general groups of Air Bypass Valves, normally closed and normally open. Each group is available in remote (in-line) versions or pump mounted versions.

Normally Closed Air Bypass Valves:

NORMALLY CLOSED BYPASS VALVE
These valves supply air to the exhaust system with medium and high applied vacuum signals during normal operation (engine warm), short idles and some accelerations. With low or no vacuum applied, the pump air is dumped through the silencer ports of the valve, or through the dump port. Operation is as follows:
1. With vacuum off at vacuum nipple, valve is closed, no air to outlet. The air then vents through polyester silencer and vent ports.
2. With vacuum on, valve opens, air flows to outlet.



NORMALLY OPEN BYPASS VALVES
Normally open valves are available with or without vacuum vents. There are different test procedures for both.

Normally Open Air Bypass Valves W/Vacuum Vents:

W/VACUUM VENTS
These valves provide a timed air dump during decelerations and also dump when a vacuum pressure difference is maintained between the signal port and the vent port. The signal port must have 3 in-Hg (10 kPa) more vacuum than the vent port to hold the dump. This mode is used to protect the catalyst from overheating.

Normally Open Air Bypass Valves:

W/OUT VACUUM VENTS HEAVY DUTY
These valves provide a timed air dump during decelerations and also dump when a vacuum pressure difference is maintained between the signal port and the vent port. The signal port must have 3 in-Hg (10 kPa) more vacuum than the vent port to hold the dump. This mode is used to protect the catalyst from overheating.

Normally Open Air Bypass Vales Without Vacuum Vent:

W/O VACUUM VENTS
These valves provide a timed dump of air for 1.2 or 2.8 seconds when a sudden high vacuum of about 20 in-Hg (68 kPa) is applied to the signal port. This prevents backfire during deceleration.

Normally Open Without Vacuum Vent:

W/O VACUUM VENTS HEAVY DUTY
These valves provide a timed dump of air for 1.2 or 2.8 seconds when a sudden high vacuum of about 20 in-Hg (68 kPa) is applied to the signal port. This prevents backfire during deceleration.