Posted 2/11/2018 17:41 (#6571037 - in reply to #6570108) Subject: RE: Raven Fast Close valve
Southern Minnesota Between Freeborn & Wells
With a fast valve , very short “shots” of 12v are sent to nudge the valve either open with one polarity or the opposite polarity to nudge it closely slightly.
Actually with a Raven controller such as a 440/450, if the applied rate is slightly low, the system will send two or three “shots” of the proper polarity but then send one shot of the opposite polarity to act as a brake so the valve doesn’t go too far.
When application is to stop, and the system is set as fast close, the system sends a constant 12v of the decrease polarity so the valve closes as fast as possible. An internal limit switch in the motor housing stops the motor from going too far.
When application is again desired, the system goes to full increase until the applied rate exceeds the target rate and the backs down. This is necessary since the system has no way to remember the last position when it was applying.
This is one if the reasons I prefer a two valve system for NH3 rather than a single fast close valve. With a two valve system, the control valve does not need to move when application stops.
I used to install Increase/Decrease LEDs in 440/450 controllers. This allowed the operator to observe the action of the control circuit. With a controller set to Fast Close the action described above was observed