Its a strange one.
I take it from post #1 that there is no problem on pump speed 1?, if that is a UPS 2 pump with proportional pressure (PP) control then fixed speed 1 is 4M, 2 is 5M and 3 is 6M, one would think that speed 1 should be sufficient, also is the cylinder return combined with other returns ?, it may be acting as a unrestricted by pass, if that red gate valve isn't a balancing valve on the cylinder return then you might consider fitting one and see if that has any effect. You could also try the pump on PP3 setting but if a fixed speed1 setting of 4M isn,t sufficient then IMO PP3 will be too weak also at < 3M.
I take it from post #1 that there is no problem on pump speed 1?, if that is a UPS 2 pump with proportional pressure (PP) control then fixed speed 1 is 4M, 2 is 5M and 3 is 6M, one would think that speed 1 should be sufficient, also is the cylinder return combined with other returns ?, it may be acting as a unrestricted by pass, if that red gate valve isn't a balancing valve on the cylinder return then you might consider fitting one and see if that has any effect. You could also try the pump on PP3 setting but if a fixed speed1 setting of 4M isn,t sufficient then IMO PP3 will be too weak also at < 3M.