What should I do with the pipe gauges?

Hint 1 of 9:

Did you click on them?  The man was obviously here.  The gauges must be
important.

Hint 2 of 9:

Notice that one gauge, at the very bottom, never changes no matter what you
do with the wheels.

Hint 3 of 9:

Your object is to set the other four to match what is set on the bottom
gauge.

Hint 4 of 9:

Notice that multiple gauges will sometimes move when you turn a single wheel.

Hint 5 of 9:

But that's only if one gauge isn't already all the way to the left or right. 
You can often move just one of those gauges by turning a wheel until the
other one in the pair stops -- just keep turning the wheel.

Hint 6 of 9:

The following solution worked most of the time.  Some fine tuning might be
necessary.

Hint 7 of 9:

Label the gauges A to D from left to right; skip the gauge that doesn't move.
 Label the wheels (valves) 1 to 4 from left to right.

Hint 8 of 9:

Turn wheel 3 clockwise to set gauge B to 30.  Turn wheel 2 clockwise to set A
to 40.