Its seven port design places the needle tip very close to the sample loop allowing partial loop filling and minimizing sample waste. Both the 8125 and 7725 use the convenient single point sealing pressure adjustment. The 7520 four port valve uses internal rotor cavities to measure sample volumes. This allows very low volumes to be injected with minimal dispersion for micro-bore chromatography. The 7010 is a six port valve that requires an optional loop filler port.
Automatic actuators are available for most valves.
The walls of the sample loop interact with your injected volume. Material against the wall moves at a much slower rate than the center of the flowing material. Larger samples will begin to lose sample material and fail to displace mobile phase. When partial loop filling, very little sample is wasted. Sample size may be more accurately controlled using the volume of the sample loop.