This 400 Series (24VDC/5.4W) is a 4-way spool valve with reverse pilot operated by a small, direct operated 4-way solenoid valve with light kit – a one-off in air valve manufacturing.  The 4-way pilot means a low minimum operating pressure – no piston adapters – and minimal resistance to shifting.  The balanced design in the pilot means shifting forces are consistently high and response times are repeatable regardless of inlet pressure fluctuations.