This paper reports on a study that investigated the effect of composite contaminants on the wear of ball type valves. The objective was to develop a contamination control theory for predicting valve contaminant service life based on various mixture ratios of a silica test contaminant and a ferrous test contaminant. Filter specifications were determined which ensure valve contaminant service life.Theoretical considerations drew on contamination control theory and new relationships are introduced which account for ball valve wear due to two contaminants. Experimental tests were conducted with the Zeta test machine to establish particle abrasivity ratings and with the valve contaminant test stand to determine valve pressure degradation to contamination.It was found that less abrasive particles result in less valve performance degradation. This result substantiated the theoretical expressions relating the valve wear composite contaminant sensitivity coefficients.