Adjust Hydraulic Pressure Relief Valve

Recently purchased a used JCB 1CX. I attached a snowblower to the high flow circuit of the machine and it does not perform as one would expect. The blower calls for 55 lpm. From the specs I can locate it appears that the displacement rating for the high flow circuit on the machine is 90 lpm @ 3600 rpm. It says the maximum working pressure is 2785 lbs. (although these specs are for a serial number before mine). To me it seems that the high flow circuit should have more than enough capacity to run that blower. However, I have to go painfully slow with the blower through the snow or it just won't throw it far enough, it will just kind of flop out of the chute. I had someone put a flow meter on the circuit and they got 94 lpm of flow at zero pressure. As he turned up the pressure resistance at the meter it dropped to 54 lpm at 2000 lbs. pressure resistance at which point the sound changes as if the pressure relief valve opens. I get the same sound if I load up the snow blower with snow... one can hear what I would describe as very pronounced "hissing" noise which I am guessing is coming from the pressure relief valve opening prematurely. I have a few questions.



First, is it typical for the flow rate to decrease as the pressure increases or should that circuit provide 90 lpm at 2785 lbs. pressure?

Second, is this particular relief valve adjustable and where can I find it?

Is there anything else I should look?



Thanks.

Adjust Hydraulic Pressure Relief Valve