Posted 3/26/2020 08:30 (#8139793 - in reply to #8138558) Subject: Why Calibrated Reflow
Southern Minnesota Between Freeborn & Wells
For those who might be trying to follow this, the reason for the calibrated reflow is that many Hardi sprayers use a Positive Displacement pump. That means the flow must go somewhere. If a boom section is shut off, that flow needs to go back to the tank since if it were just blocked off, the product would need to be forced out the sections that are still ON causing an over application. Worse yet, if all sections are shut off they product has nowhere to go.
This means that the control valve and the ON/OFF valves must bypass or return the excess back to the tank. It is necessary that these return paths from the valves provide the same amount of back pressure that the boom section does so that shutting some off doesn't have an effect on those that are still on.
If all the booms are the same width and you use only one tip throughout the year, it is reasonable to get the proper orifices to properly restrict the back pressure. If the booms are different widths and/or different tips are used throughout the year this back pressure business becomes a pain.
The plumbing and logic is much easier to follow with a Centrifugal pump which is NOT a positive displacement type. The output from a Centrifugal pump does not need to go somewhere although some flow is desirable so as not to build up excessive heat in the pump. This is generally not an issue since an agitation line is commonly tee'd off the outlet of the pump to provide agitation and some product movement.
The Micro Trak folks had a different approach which could be used with these positive displacement setups. They had a controller that could work with two flow meters. One flow meter measured the flow as usual which might be the entire flow from the pump. The returns from the control valve and ON/OFF paths were combined and ran through a second flow meter. The system calculated the actual flow getting to the ground by subtracting the flow value from the return flow meter from the main flow meter. This should correctly represent the flow actually getting to the ground. The problem of providing the proper amount of back flow resistance would still be a nuisance.
Their second flow meter could be setup as a fill flow meter if desired. The first flow meter controlled the sprayer as usual but the second was only used to fill the tank. I really never set one of these up but thought the idea was rather clever.