7
SECTION VIEW DRAWING AND DESCRIPTION –
SERIES 746 DRY ACCELERATOR
The Series 746 Dry Accelerator exhausts air from the actuator to speed the operation of the valve.
A diaphragm separates the Series 746 Dry Accelerator into two chambers. The closing chamber contains a compression
spring, which maintains this chamber in the closed position. This closed position is maintained as long as the pressure
differential between the opening and closing chambers is less than 3 psi (21 kPa).
When the system introduces air pressure into the dry accelerator, the air goes into the closing chamber and passes
through a built-in check valve to the opening chamber. The built-in check valve, which allows flow into the opening
chamber, prevents pressure from escaping the opening chamber. Therefore, air can escape only through the restrictor.
When a rapid loss of system air pressure occurs, such as an open sprinkler, air escapes from the closing chamber faster
than it does from the opening chamber. As the sprinkler system’s pressure continues to decay, a differential pressure
develops across the diaphragm. When this differential pressure reaches 3 – 5 psi (21 – 34 kPa), the opening chamber’s
pressure overcomes the compression spring’s closing force, causing the closing chamber to open to the atmosphere.
The closing chamber opens immediately and releases pressure from the actuator, resulting in valve operation.
To Pressure
Gauge
Air Inlet from
Actuator
14
11
12
13
10
9
8
7
4
6
5
3
1
2
15
Exaggerated for Clarity
BILL OF MATERIALS
Item
Description
Item
Description
1
Opening Chamber
9
o-ring
2
Restrictor
10
Seal Support
3
Piston
11
Closing Chamber Seal
4
o-ring
12
Button Head Cap Screw
5
Diaphragm
13
Washer
6
Actuator Shaft
14
Adjustable Seat
7
Closing Chamber
15
Built-In Check Valve
8
Compression Spring
DISCONTINUED
PRODUCT
