Description
Flow is allowed bi-directionally between 2 and 3, and blocked at 4 until pressure at 1 rises to overcome the spring bias against the spool. When this bias pressure is surpassed, the spool shifts, allowing bi-directional flow between 3 and 4 while blocking 2. The port 5 to be connected with the external drain, allowing consistent shifting with only spring bias pressure independent of conditions at 2, 3 and 4.