Index: firmware/App/Controllers/PresOccl.c
===================================================================
diff -u -r68e6a5f41d4e9decee2658b3421f34892c9b9ac7 -rbafeddaeaa68c011354968c38ff38b8f43085151
--- firmware/App/Controllers/PresOccl.c	(.../PresOccl.c)	(revision 68e6a5f41d4e9decee2658b3421f34892c9b9ac7)
+++ firmware/App/Controllers/PresOccl.c	(.../PresOccl.c)	(revision bafeddaeaa68c011354968c38ff38b8f43085151)
@@ -77,7 +77,7 @@
 #define VENOUS_PRESSURE_LIMIT_MAX_MMHG      ( 400.0F )                                      ///< Maximum venous pressure limit (in mmHg).
 #define VENOUS_PRESSURE_LIMIT_MIN_MMHG      ( 20.0F )                                       ///< Minimum venous pressure limit (in mmHg).
 #define VENOUS_PRESSURE_OCCL_OFFSET_MMHG    ( 50.0F )                                       ///< Venous pressure occlusion threshold offset from max alarm limit (in mmHg).
-#define VENOUS_PRESSURE_LIMIT_DELAY_MS      ( SEC_PER_MIN * MS_PER_SECOND )                 ///< Venous pressure limit delay period following dialysis start/resume (use wider limits during this period).
+#define VENOUS_PRES_AIR_TRAP_FILL_DELAY_MS  ( ( 5 * MS_PER_SECOND ) / TASK_GENERAL_INTERVAL )  ///< Venous pressure low exemption delay (in task intervals) following an air trap fill.
 
 #define PSI_TO_MMHG                         ( 51.7149F )                                    ///< Conversion factor for converting PSI to mmHg.
 
@@ -86,7 +86,6 @@
 #define VENOUS_PRESSURE_STALE_DATA          2                                               ///< Venous pressure status bits indicate data is stale (no new data since last fpga read).
 #define VENOUS_PRESSURE_DIAG_CONDITION      3                                               ///< Venous pressure status bits diagnostic condition (alarm).
 
-// The new arterial pressure sensor is the same as the venous pressure sensor
 #define ARTERIAL_PRESSURE_NORMAL_OP         0                                               ///< Arterial pressure status bits indicate normal operation.
 #define ARTERIAL_PRESSURE_CMD_MODE          1                                               ///< Arterial pressure status bits indicate sensor in command mode.
 #define ARTERIAL_PRESSURE_STALE_DATA        2                                               ///< Arterial pressure status bits indicate data is stale (no new data since last fpga read).
@@ -100,7 +99,7 @@
 #define MAX_OCCLUSION_COUNTS                32766                                           ///< Maximum occlusion sensor reading for range check.
 #define OCCLUSION_CARTRIDGE_LOADED_PRESSURE_READING_MAX         24500                       ///< Occlusion sensors maximum pressure reading limit when cartridge is considered loaded.
 
-#define EMPTY_SALINE_BAG_THRESHOLD_MMHG     -300.0F                                         ///< Threshold below which the saline bag is considered empty (in mmHg).  TODO - get real threshold from Systems
+#define EMPTY_SALINE_BAG_THRESHOLD_MMHG     -300.0F                                         ///< Threshold below which the saline bag is considered empty (in mmHg).
 static const U32 EMPTY_SALINE_BAG_PERSISTENCE = ( 250 / TASK_GENERAL_INTERVAL );            ///< Time that saline bag looks empty before saying it is empty.
 
 #define PRES_ALARM_PERSISTENCE              ( 1 * MS_PER_SECOND )                           ///< Alarm persistence period for pressure alarms.
@@ -143,7 +142,8 @@
 // ********** private data **********
 
 static PRESSURE_STATE_T presOcclState;                                          ///< Current state of pressure monitor state machine.
-static U32 presOcclDataPublicationTimerCounter = 0;                             ///< Used to schedule pressure data publication to CAN bus.
+static U32 presOcclDataPublicationTimerCounter = 0;                             ///< Used to schedule pressure data publication to CAN bus.
+static U32 venLowPresExemptAfterAirTrapFillTimerCtr;                            ///< Exempt low ven pressure limit alarm for a time following an air trap fill.
 
 /// Interval (in ms) at which to publish pressure/occlusion data to CAN bus.
 static OVERRIDE_U32_T presOcclDataPublishInterval = { PRES_OCCL_DATA_PUB_INTERVAL, PRES_OCCL_DATA_PUB_INTERVAL, 0, 0 };
@@ -228,18 +228,19 @@
 
     setPressureLimitsToOuterBounds();
 
-    currPresLimitsState                     = PRESSURE_LIMITS_STATE_OFF;
-    pressureLimitsActive                    = FALSE;
-    stabilizationStartTimeMs                = 0;
-    stableArterialPressure                  = 0;
-    stableVenousPressure                    = 0;
-    longFilteredArterialPressure            = 0.0F;
-    shortFilteredArterialPressure           = 0.0F;
-    shortFilteredVenousPressure             = 0.0F;
-    presOcclDataPublicationTimerCounter     = DATA_PUBLISH_COUNTER_START_COUNT;
-    presOcclState                           = PRESSURE_WAIT_FOR_POST_STATE;
-    presOcclPostState                       = PRESSURE_SELF_TEST_STATE_START;
-    bloodPumpOcclusionAfterCartridgeInstall = 0;
+    currPresLimitsState                      = PRESSURE_LIMITS_STATE_OFF;
+    pressureLimitsActive                     = FALSE;
+    stabilizationStartTimeMs                 = 0;
+    stableArterialPressure                   = 0;
+    stableVenousPressure                     = 0;
+    venLowPresExemptAfterAirTrapFillTimerCtr = 0;
+    longFilteredArterialPressure             = 0.0F;
+    shortFilteredArterialPressure            = 0.0F;
+    shortFilteredVenousPressure              = 0.0F;
+    presOcclDataPublicationTimerCounter      = DATA_PUBLISH_COUNTER_START_COUNT;
+    presOcclState                            = PRESSURE_WAIT_FOR_POST_STATE;
+    presOcclPostState                        = PRESSURE_SELF_TEST_STATE_START;
+    bloodPumpOcclusionAfterCartridgeInstall  = 0;
 }
 
 /*********************************************************************//**
@@ -722,7 +723,18 @@
 static void checkVenousPressureInRange( void )
 {
     F32 venPres = getFilteredVenousPressure();
+    OPN_CLS_STATE_T airTrapValveState = getValveAirTrapStatus();
 
+    // track time since last air trap fill
+    if ( STATE_OPEN == airTrapValveState )
+    {
+        venLowPresExemptAfterAirTrapFillTimerCtr = 0;
+    }
+    else
+    {
+        venLowPresExemptAfterAirTrapFillTimerCtr++;
+    }
+
 #ifndef _RELEASE_
     if ( getSoftwareConfigStatus( SW_CONFIG_DISABLE_VENOUS_PRESSURE_CHECK ) != SW_CONFIG_ENABLE_VALUE )
 #endif
@@ -742,7 +754,7 @@
             venPresHigh = ( venPres > (F32)currentVenousMaxLimit ? TRUE : FALSE );
 
             // Check venous pressure is within alarm limits
-            if ( getValveAirTrapStatus() != STATE_OPEN )
+            if ( ( airTrapValveState != STATE_OPEN ) && ( venLowPresExemptAfterAirTrapFillTimerCtr > VENOUS_PRES_AIR_TRAP_FILL_DELAY_MS ) )
             {
                 if ( TRUE == isPersistentAlarmTriggered( ALARM_ID_HD_VENOUS_PRESSURE_LOW, venPresLow ) )
                 {