Necessity is the mother of invention. Die castings have evolved from shapes that you can manufacture with an open shut die, into the current typical die casting that has slides and cores. This is to make a die casting more valuable than a stamping. Staying in business as a die caster involves upgrading the casting machines to support dies with more slides and subcores.

Subcores have difficult die design issues when they are larger than 25mm in diameter. The intensified metal pressure on the front of the subcore easily can exceed the locking force applied by the hydraulic cylinder. The core blows back when this is true. This problem is even worse when the casting machine can only deliver 1500 psi (103 bar) hydraulic pressure. Older casting machines may compound the difficulty by dropping hydraulic pressure due to shot motion. The traditional solution is to use a subcore lock run by an additional cylinder. This solution become problematic when the number separate cylinder motions exceeds the available core valves on the machine. Even more of a problem when a OEM PLC program lock prevents implementing the cylinder motion cycles needed to support a slide lock

Enter the creative solution. Pilot check valves prevent fluid from exiting from hydraulic cylinders when the direction valve is not energized. My first attempt was to stack a pilot check valve under the direction valve on the machine. Unfortunately the hoses balloon to much and unacceptable blow back occurs. The successful implementation of pilot check valves came by using a custom manifold on a O-ring port hydraulic cylinder. The rigid connection between the cylinder and D05 pilot check stopped blow back. As a bonus the full pilot check valve rated 350 bar holding pressure was available even though the machine only had 1500 psi-100 bar or less of hydraulic pressure (you also need cylinders that can handle (5000 psi- 350 bar pressure)