Has anyone experienced problems with this model of pump not keeping a constant flow at different pressures.

Currently the pump we are having serviced has generated the following results;

Barr - Flow (ml/min)
76 - 1.0
103 - 0.96
133 - 0.90
154 - 0.88
198 - 0.80

this generates a -0.99753 correlation coefficient. Only water was used for mobile phase.

Each data point was taken after collecting the mobile phase for 10 min. Is there a parameter that needs to be adjusted? We are in a real jam. So if anyone can help, please do.

Thanks

Chuck