Figure 5.

Flow gain curves for the HRV (blue line) and ULLV (black line). The HRV presents a constant flow increasing of about 2.3 l/min/mA until near 2 mA, when the valve gain start decreasing. The ULLV, instead, presents a low flow gain of 0.4 l/min/mA and a high flow gain of $\pm$2.5 l/min/mA inside and outside the current range of $\pm$1.2 mA, respectively. Note: these curves were obtained from experimental measurements considering the valve redundant coils (2 coils) in series. The ISA and smart manifolds integrate these valves with the coils connected in parallel to increase the operation safety. In this case, the scale of the current is doubled and the current command ranges from $\pm$10 mA.