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Operation
Automatic Fail-Safe System
Page 12
Table 2: Valve Stem Detection Conditions
Upper Switch
Condition
Switch Symbol
Valve Closed
Valve Open
Valve Closed with
Upper Seat Lift
Valve Closed with
Lower Seat Lift
1 = Energized; LED is lit
Upper Switch – Sends input signal when valve is properly open.
Lower Switch – Sends input signal when valve is properly closed.
Yoke Switch – Sends input signal when upper seat is properly closed.
The valve seats are part of an automatic fail-safe system preventing
contamination of product with cleaning or sanitizing solutions. Automatic fail-
safe systems are unique to each particular installation. Typically, both blocking
valve seats are properly seated in blocked position before the mechanical
cleaning system can be activated for the cleaning circuit containing the valve
arrangement. W75RS PMO valves are spring-to-closed fail-safe into the blocked
position. Waukesha Cherry-Burrell does not offer control systems, only the PMO
double seat valve. To determine the integrity of fail-safe control interlocks, see
"Positive Fail-Safe Detection Test" on page 14.
95-03076
Waukesha Cherry-Burrell
Lower Switch
(NO)
(NC)
0
1
1
0
0
1
0
0
0 = De-energized; LED is off
Yoke Switch
(NC)
1
0
0
1
August 2008
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