Pre-Fill Valve (PF)
Feature: Compact construction, available for large flow, no leaking. It must leak the pressure before turning on.
Function: A drain valve between hydraulic cylinder and tank.
During operation in a large pressure mechanism, it needs to suck oil from tank to hydraulic cylinder. While pressurizing, it prevents the oil flowing from hydraulic cylinder to tank. When reversion, hydraulic cylinder will make oil draining to tank.