VALVE OPERATION

PRINCIPLES OF DIGITAL CONTROL SYSTEMS
The 115-3 valve is the basis for both the Model 22 and Model 88 systems. It is modulated, or positioned, by its two solenoid pilots (2) and (3). With pilot (2) closed and pilot (3) open, the diaphragm chamber of the main valve (1) is vented to downstream, and the valve moves further open. Conversely, with pilot (2) open and pilot (3) closed, inlet pressure is applied to the main valve diaphragm chamber, moving the valve further closed. Finally, with both pilots closed, the diaphragm chamber is “hydraulically locked” (no flow on or off the chamber), and the valve holds its position. This locking action gives the valve extreme stability, even at highly-throttled positions.

SERIES 22
In the Model 22 system, the analog process signal (PV) is received by the controller from the transducer and compared to the programmed set point. If the PV is outside the small dead band around the set point, the controller begins pulsing the appropriate solenoid pilot open and closed on a time proportional basis, with the amount of open time proportional to the deviation from the set point. Hydraulic locking occurs when the process variable is within the dead band around the set point. The pulsing action enables the set point to be maintained within close limits, with a minimum of overshoot or "hunting" when process conditions change.

SERIES 88
In the Model 88, the analog "command" signal is input to the Logic Unit, which converts the signal to a digital one. It then compares this digital signal to the digital signal from the valve position transmitter* which is reporting actual valve position (% open). If the two signals are different, the logic unit opens the appropriate solenoid pilot to either open or close the valve. When the signals match, the logic unit closes both solenoid pilots, resulting in hydraulic lock. The valve will stably hold its position until the command signal again changes.

* The OCV Digital Valve Position Transmitter is a non-contact type, impervious to the effects of wear, electrical noise and drift. Installed and “zeroed” in the closed position, no further adjustment is required.


APPLICATION CHART

 





CONTROLLERS & VALVE POSITION TRANSMITTER

 Power/Signal Failure Modes
Both the model 22 and 88 valves can be configured to either close, open or hold last position in the event of electrical power or signal failure.

Hydraulic Pilot Backup System
The valve can be configured with a full pilot system to provide control backup in the event of power failure. They can also provide additional limiting controls in conjunction with the electronic positioned function. See Valve Selection Guide for specific model combinations.

Low Pressure Applications
Both the 22 and 88 are line-pressure-operated valves. In those cases where line pressure is too low or otherwise unsuitable for valve operation, the desired function can still be provided through the use of a power-actuated main valve (model 66) and independent pressure source. See Valve Selection Guide for specific model combinations.
Each series is supplied with an OCV control module. These are supplied in a NEMA 4X enclosure.

Enclosure overall dimensions:
16” High x 12 ” Wide x 8 ”

Deep Valve Position Transmitter:

Enclosure:  NEMA 4
TOLL FREE 1.888.628.8258  |  phone: 918.627.1942  |  fax: 918.622.8916  |  7400 East 42nd Place, Tulsa, Oklahoma 74145