By adding the 4 Link Closer to the closing wheels you eliminate the blank areas through ditches and over the tops of terraces. These new 4 bar linkages give you nearly double the travel (up to 9″) of the present day swing arm tail sections.
The standard swing arm tail section found on a majority of the planters built today has a limited amount of travel up and down (roughly 4″) throughout full movement when planting. If you have ditches to cross or terraces to plant over then the amount of travel is limited to 2″ both ways of center. Sometimes this isn’t enough—giving poor seed to soil contact by not closing the seed V properly or leaving seeds on top of the ground.
Whenever the press wheels flex up, the contact points on the press wheels get wider, causing them to be toe out and they tend to over cover the width of the seed V. When the press wheels go down past center, they under cover or toe in, causing the seed V to not close properly.
Also, when you max out the wheels on the top side, it can raise the planter unit out of the ground, causing seed depth to change. By running extra spring pressure on the press wheels you create up pressure on the row units. Thus, as the planter travels through the field at speeds above 5mph, the swing arm closing system is constantly moving up and down along with the parallel linkage of the planter unit itself, causing uneven depth control.
When planting up and over terraces, sometimes there are areas over the top of the terrace where the double discs of the planter are totally out of the ground (planting seeds on top of the ground), and the press wheels are carrying the weight of the whole planter on one side or the other of the terrace. Then, on the opposite side of the terrace, the double disc openers are totally bottomed out for depth and the press wheels are off the ground, not closing the furrow. This leaves several feet of seeded area across a ditch or terrace that is blanked out due to poor seed to soil contact.