Regulators are large boxes with one side attached via an expandable bellows section,
usually leather. They have springs and or weights to preload the side (usually actually
the top surface). When the instrument has wind up, this reservoir fills and its position
acts to admit more or less air, regulating the pressure. In an instrument like this one,
different ranks of pipes may use different wind pressure, so there may be multiple
regulators to supply different pressure from the same blower and wind pipe.