The check valve just prevents it from drifting but wont stop gravity from acting faster than the pump when the thing is cycled. The check valve also prevents it from ever being used with float
I will start there. ThanksI doubt that you will find a double pilot operated check valve that will go onto your cylinder like the typical off-the-shelf top link units have as pictured in post #4. Those take 3/8" British pipe thread and your ports are most likely #6 oring boss.
I recommend putting .031 orifice fittings on each port and your issue should be resolved.![]()