Filters with removable frits are designed to compensate for the thickness of the filter element - the resulting pilot depths are identical with the rest of the Valco product line, facilitating interchangeability of made up fittings. Therefore, although our filters look very much like our unions, they are not interchangeable with unions; a filter with its frit removed should not be substituted for a union, because the space designed for the frit introduces dead volume into the system.
In addition, since filter bodies are coned, they will have dead volume when used as a union even if the tubing is made up in the filter with a longer, non-standard pilot length.
FIGURE 1: A filter with removable frit, coned for uniform flow and maximum filter surface.
FIGURE 2: The same filter with the frit removed, being used as a reducing union. The fitting was properly made up in a Valco union, so dead volume is created where the frit should be.
FIGURE 3: The same situation as FIGURE 2, but with the fitting made up in the filter. There is still dead volume from the cone in the filter body.
