Thanks Guys - am redoing my sparge tank (a new version of top 1/2 section smaller dia electric hot water tank)- I work in the water and wastewater industry and there are a number of variations on upflow filters which I thought might be beneficial to have less recirculation and take advantage of gravity to clear wort by leaving 3 or 4 " on top of bed, only need to regulate water to bottom to regulate velocity in the bed. Am thinking if Martin gave it a go and gave up, continuation of the idea is probably not good use of my time!