diff --git a/iblrig/gui/valve.py b/iblrig/gui/valve.py
index 09d63595b..1352f34c5 100644
--- a/iblrig/gui/valve.py
+++ b/iblrig/gui/valve.py
@@ -49,7 +49,7 @@ def update(self):
         if len(self.values.open_times_ms) < 2:
             self._curve.setData(x=[], y=[])
         else:
-            time_range = list(np.linspace(self.values.open_times_ms[0], self.values.open_times_ms[-1], 100))
+            time_range = list(np.linspace(0, self.values.open_times_ms[-1], 100))
             self._curve.setData(x=time_range, y=self.values.ms2ul(time_range))
 
     def clear(self):
diff --git a/iblrig/valve.py b/iblrig/valve.py
index 19b52f1a6..14e58f42b 100644
--- a/iblrig/valve.py
+++ b/iblrig/valve.py
@@ -76,7 +76,7 @@ def ms2ul(self, time_ms: NonNegativeFloat | Iterable[NonNegativeFloat]) -> NonNe
         elif time_ms == 0.0:
             return 0.0
         else:
-            return self._polynomial(time_ms)
+            return max(np.append(self._polynomial(time_ms), 0.0))
 
 
 class Valve: