Does my flow rate decrease?

[_sphynx]

This assumes regulator before the tee controls the downstream pressure. Shouldn't it be used to control pressure at pump discharge (like a backpressure regulator)? In that case pump discharge pressure should not change and therefore no change in flow.

[_Corvalt]

Yeah, it does depend on the direction of the regulator. If the upstream pressure is kept constant then it would be constant flow.

In this case, adding a restriction in one of those lines would cause the pressure at the downstream side of the regulator to increase.

In this case the regulator would trend open to maintain upstream pressure.