No, a valve will not work.  The flow is so low and inconsistent that the pressure will equalize on both sides of the valve.  A regulator is an automatic valve that continually refills the system to the desired water column height.  If it is set to 6" of water column pressure, as water is withdrawn from the system a valve opens and refills the system to 6" of head and then the valve closes. 
 
Imagine you have a bucket attached to your drinker lines with a flexible hose.  You install a float valve in the bucket that always keeps the bucket half full with water from your drum.  You then adjust the height of the bucket so that the water level in the bucket is 6" above your drinkers, or 8", or 10", or what have you...  That is an adjustable regulator, just not as compact as the little unit attached to the drinker line in the photo above.  That one uses a rubber diaphragm that is pretensioned with an adjustable spring load to open and close that valve at the proper water column pressure.