Near Intersection of I-35 & I-90 Southern Mn. | The Raven standard and Fast control valves are the same in some respects. They both look alike from the outside and both use the Jamesbury ball valve.
Internally the Standard control valve uses a geared down motor which mechanically slows down the rate at which the ball turns. In the Fast valve no gears are used to slow down the rate at which the ball turns.
In a standard control valve due to the gearing, it will take about 8 seconds for the ball to turn from its maximum position of OPEN to the closed position. This would be much too slow for the ON/OFF function. This valve like the Raven butterfly control valve as used on sprayers is designed for control only and was purposely geared down to prevent the control loop from overshooting the target range when an adjustment was needed.
The control valve is designed to only open a maximum of about 80 degrees rather than the full 90 degrees as might be expected. The reason being that generally it is not necessary to have the ball fully open for control as those "last" 10 degrees do not add much additional flow anyway.
Historically the standard valve was created first and was designed to mimic the behavior of the spray control valve. With a standard control valve a separate On/Off valve(s) are always needed.
In an effort to reduce the price of an NH3 system, Raven created the Fast Close valve some years ago. In this arrangment a single valve handles both the ON/OFF function and control. It is called "Fast" because with a constant 12V signal, the valve will cycle very quickly which is needed for a quick response to the ON/OFF function.
This creates a problem for the control side of things. Since the motor is not geared down, the system must give a very short "shot" of electricity to move the ball slightly for the control function. In fact if the system needs to open the ball slightly, it may give the valve a couple of shots of the OPEN polarity followed by a shot of the CLOSE polarity to stop the valve from overshooting.
Since the electrical properties of the two valves are vastly different, it is necessary that the console be programmed in the proper mode for the valve being used.
I have never been a fan of the Fast valve for NH3. Since the same valve is used for control and the ON/OFF function, the system must "hunt" for the correct position for the valve when it is reopened after turning around on the ends. The system essentially opens up until the rate is too high and then brings it back down slightly.
Contrast this with a standard control valve and an ON/OFF valve. When the rig is shutoff on the ends the control valve does not move but the ON/OFF valve closes completely. When the system is turned ON, the ON/OFF valve opens completely and the since the control valve is already in the same position as when the system was shut off, it will be approximately correct.
A Fast valve can be operated in either the Fast or the Fast Close position. If a Fast valve is followed by a standard ON/OFF valve then the system can be run in the Fast mode. In this combination, the system will send the necessary short shots of electricity to the Fast valve for control purposes but will not shut the valve down to shut the system OFF since the standard ON/OFF valve is handling that function. If the Fast valve is expected to handle both the control and ON/OFF function then the console must be programmed in the FAST CLOSE mode.
There would be no reason to setup a system with a Fast valve followed by an ON/OFF valve unless one had a Fast valve lying around that they wished to use.
The Fast valve can also have problems with control at low rates since the ball may only need to be moved slightly for the correct rate adjustment. Troubleshooting a Fast system over the phone is more difficult than a standard system.
Given the dramatic increases in the price of NH3, I would recommend more than ever of going with a separate control and ON/OFF setup.
Referring to the question of converting a Standard to a Fast valve - the answer is mostly NO due to the geardown arrangment mentoned above.
Deere folks - apparently the Deere 2600 handles the Fast situation. Are they able to handle a muli-section NH3 bar or do they just support a single ON/OFF? I'm, curious as to why they use their Boom 13 as the Master.
The Ag Leader Direct Command Liquid Control module handles both the Fast and Standard setups with one or multiple booms. With multiple sections it is necessary to have an ON/OFF valve act as a Master ON/OFF with other ON/OFF valves for each section. The liquid line for the heat exchanger(s) is tee'd in between the Master ON/OFF and the section ON/OFF valves.
Edited by tedbear 9/12/2008 05:39
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Deere 2600 Display and Raven NH3
