Grizz,
The solution was to relive the system of the sudden closing of the ports whilst still handling the large amount of flow from the pump, for this I added a ball valve (which ended up being a blessing for maintenance) but is still left wide open so im not having to throttle back the pump either
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The key was to open the spool to relive the back pressure kinda like bleeding off the extra back pressure throu the closed ports, worked a treat.