| Figure 1. Modeling of a 4-way valve begins with a single land
and two describing equations, one each for the overlap and
underlap condition, and intersecting with equal slopes. | A
proposed spool valve model is based on the characteristics of a
single, variable valve land, four of which are grouped to form
the 4-way model. Each land has two regions; the first is the
overlap (closed) region in which land-to-land leakage varies in
direct proportion to the square root of the differential
pressure across the land and is inversely proportional to the
overlap distance. The second region is where the valve land is
under lapped and, therefore, is open. This is where the valve
coefficient varies in direct proportion to the land under lap
(degree of opening) and in direct proportion to the square root
of the differential pressure. It is sometimes referred to as the
straight line region. The two regions converge on the transition
point, KVXX in Figure 1. The transition point occurs at a spool
position of xX. The assum