Pull to refresh isn't an in-built feature of the grids. But using SGridDelegate's inherited UIScrollViewDelegate methods should make implementing this fairly simple. By using methods such as scrollViewDidScroll: on your grid's delegate you should be able to check the current contentOffset of the grid in order to decide when a refresh/reload is necessary. The grid can then be reloaded in the usual way [grid reload].
I hope this suggestion is useful!