The valves on the LH2 system are positioned / verified by the operators before the operation begins.

For example for the MPS (Main Propulsion System) this includes:
Verifying the Helium pressure / purge is active for the SSME's (Space Shuttle Main Engines)
The 17" and 4" Disconnect valves between the Shuttle and the ET is in the open / Latched position
The large 12" prevalves upstream of the SSME's are closed.
The Fill / Drain valves are open
The recirculation pump shutoff valves are closed
Etc.

The console operators performs several programs to verify manually or automatically that the system is ready to begin the fill operation. These programs establish that; 1) All exception monitor limits are set to their standby conditions; 2) All system measurements are being reported; and 3) All mechanical valves are cycled to determine their readiness to operate.

When the verifications are complete, the operator awaits a "go" signal from the lead test conductor. When this signal comes, the operator pushes a single button marked "Fill." The liquid hydrogen loading operation begins, and continues automatically until completion. It includes these major steps:
A) A 4 minute chilldown of the storage area through A3309 a four inch valve in the storage area. All pipes, tanks etc., have to be prechilled to prevent an excess amount of gaseous hydrogen from forming. The LH2 system did not have any pumps unlike the LO2 system, the LH2 was transferred using ullage pressure in the storage tank. Transfer is by 60psi storage tank pressure.
B) A slow fill of the Hydrogen tank at 1200 gpm to 5% through a 10" storage area valve (A3301)and reduced main fill valve on MLP
C) A "fast-fill" of the Hydrogen tank fast fill at 10000 gpm to 85%, turned on the Recirculation pumps after fast fill started and closed upstream engine prevalves (PV4, PV5, PV6). This pushed LH2 through the SSME to condition the engines for start
D) Reduced Fast Fill from 85% (as determined by a timer), inboard fill & drain PV12 is closed, fill through the 4" disconnect PD3 into the ET/LH2 tank
E) Slow fill with the ET pressurized from 98% to 100%
E) The constant replenishment of the Hydrogen boiled off and bled off in gaseous form at about 100 gpm until about T-1:57 before launch
F) At ignition minus 1 minute 57s minutes, the liquid hydrogen tank is no longer filled from the ground, pressurized and ready for launch.

Some 200 computer programs are required to operate all these phases of action. They operate a primary pump or secondary pump, primary fill valve, etc., throughout a complex piping system. While these programs are in process, hundreds of measurements are constantly monitored to be certain all temperatures, pressures, etc., are within limits. If a condition is detected which requires immediate corrective action, the program takes that action and notifies the operator. Less immediate problems are called to the operator's attention for his consideration. The operator has the option to alter the sequence of events or take over control, in the unlikely event that he or she should think it necessary.

The loading of liquid Hydrogen is only one of hundreds of equally complicated, difficult operations performed automatically by the LPS, while operating under stringent safety and performance requirements. The end result is the launch of a Space shuttle