In the case of the series I HP1090 the valve functions well at a 1-5 L flow rate. Next the flow is directed from the valve to the capillary column. Find the port out of the switching valve that normally directs flow to the column and replace it with 50 M ID fsc. At this point if your HPLC has column temperature control capability you can control for retention time variability by placing the capillary column in the heated column compartment. If your HPLC system does not have column temperature control capabilities, column heating jackets are commercially available.
Heat transfer is very efficient for most capillary designs since the column diameters are small.
Column temperature control is not mandatory but as with standard columns it will help with peak retention time reproducibility and will add another dimension of chromatographic control. The tee could potentially be another source of temperature induced variation. The heated column compartment can be conveniently used to control the temperature of the tee, see Figure 3. Once the capillary HPLC is established one must be concerned with UV detection. Standard HPLC flow cells have internal volumes that are too large for the low flow rates of capillary columns.