Quantity that is double the filtrate volume collected from a filtration test between 7. 5 to 30 minutes. This ignores the spurt of filtrate that comes out of the filter press before a cake is established. Relative filtrate volume is used to evaluate certain mud materials. Relative filtrate volume can be expressed as Vrel, = (V₃₀ - V_{7. 5}) x 2. Static filtration theory holds that filtrate volume increases as the square root of time. Thus, the volume from 0 to 7. 5 minutes should be the same as from 7. 5 to 30 minutes in the case of no spurt loss in the first interval. Because spurt often occurs in the 0 to 7. 5 minutes, those data can be ignored by doubling the volume in the second interval. This practice has no bearing on dynamic filtration or on high-pressure, high-temperature filtration tests.