diff --git a/.pylintrc b/.pylintrc
index 21527bf..6180ea0 100644
--- a/.pylintrc
+++ b/.pylintrc
@@ -218,7 +218,7 @@ max-branches=50
 max-statements=150
 
 # Maximum number of parents for a class (see R0901).
-max-parents=15
+max-parents=25
 
 # Maximum number of attributes for a class (see R0902).
 max-attributes=50
diff --git a/Makefile b/Makefile
index 6e4f543..3148ea2 100644
--- a/Makefile
+++ b/Makefile
@@ -38,7 +38,7 @@ doc:
 	$(MAKE) -C doc html
 
 lint:
-	pylint -j 0 -f colorized -r n --rcfile=.pylintrc secop secop_* test
+	pylint -f colorized -r n --rcfile=.pylintrc secop secop_* test
 
 isort:
 	@find test -name '*.py' -print0 | xargs -0 isort -e -m 2 -w 80 -ns __init__.py
diff --git a/secop_psi/mercury.py b/secop_psi/mercury.py
index abd5be3..deb4a9e 100644
--- a/secop_psi/mercury.py
+++ b/secop_psi/mercury.py
@@ -327,15 +327,15 @@ class HeaterOutput(HasInput, MercuryChannel, Writable):
         self._last_target = self._volt_target ** 2 / max(10, self.resistivity)
         return self._last_target
 
-    def set_target(self, value):
+    def set_target(self, target):
         """set the target without switching to manual
 
         might be used by a software loop
         """
-        self._volt_target = math.sqrt(value * self.resistivity)
+        self._volt_target = math.sqrt(target * self.resistivity)
         self.change('HTR:SIG:VOLT', self._volt_target)
-        self._last_target = value
-        return value
+        self._last_target = target
+        return target
 
     def write_target(self, value):
         self.write_controlled_by(SELF)
@@ -482,13 +482,13 @@ class PressureLoop(HasInput, PressureSensor, Loop, Drivable):
     def read_target(self):
         return self.query('PRES:LOOP:PRST')
 
-    def set_target(self, value):
+    def set_target(self, target):
         """set the target without switching to manual
 
         might be used by a software loop
         """
-        self.change('PRES:LOOP:PRST', value)
-        super().set_target(value)
+        self.change('PRES:LOOP:PRST', target)
+        super().set_target(target)
 
     def write_target(self, value):
         self.write_controlled_by(SELF)
diff --git a/secop_psi/phytron.py b/secop_psi/phytron.py
index 5fcdbf9..14f596e 100644
--- a/secop_psi/phytron.py
+++ b/secop_psi/phytron.py
@@ -34,13 +34,11 @@ class PhytronIO(StringIO):
     timeout = 0.5
     identification = [('0IVR', 'MCC Minilog .*')]
 
-    def communicate(self, command, expect_response=True):
+    def communicate(self, command):
         for ntry in range(5, 0, -1):
             try:
                 _, _, reply = super().communicate('\x02' + command).partition('\x02')
                 if reply[0] == '\x06':  # ACK
-                    if len(reply) == 1 and expect_response:
-                        raise CommunicationFailedError('empty response')
                     break
                 raise CommunicationFailedError('missing ACK %r' % reply)
             except Exception as e:
@@ -77,7 +75,7 @@ class Motor(PersistentMixin, HasIO, Drivable):
     _backlash_pending = False
     _mismatch_count = 0
     _rawlimits = None
-    _step_size = None
+    _step_size = None  # degree / step
 
     def earlyInit(self):
         super().earlyInit()
@@ -92,7 +90,7 @@ class Motor(PersistentMixin, HasIO, Drivable):
         return self.communicate('\x02%x%s%s' % (self.address, self.axis, cmd))
 
     def set(self, cmd, value):
-        self.communicate('\x02%x%s%s%g' % (self.address, self.axis, cmd, value), False)
+        self.communicate('\x02%x%s%s%g' % (self.address, self.axis, cmd, value))
 
     def set_get(self, cmd, value, query):
         self.set(cmd, value)
diff --git a/secop_psi/triton.py b/secop_psi/triton.py
index b03d4e9..998b162 100644
--- a/secop_psi/triton.py
+++ b/secop_psi/triton.py
@@ -21,8 +21,7 @@
 """oxford instruments triton (kelvinoxjt dil)"""
 
 from math import sqrt
-from secop.core import Writable, Parameter, Readable, Drivable, IDLE, WARN, BUSY, Done
-from secop.errors import HardwareError
+from secop.core import Writable, Parameter, Readable, Drivable, IDLE, WARN, BUSY, ERROR, Done
 from secop.datatypes import EnumType, FloatRange
 from secop.lib.enum import Enum
 from secop_psi.mercury import MercuryChannel, Mapped, off_on, HasInput, SELF
@@ -62,7 +61,7 @@ class Action(MercuryChannel, Writable):
     # PCOND (pause pre-cool (not condense?) automation)
     # RCOND (resume pre-cool (not condense?) automation)
     # WARM (warm-up)
-    # EPCL (empty pre-coll automation)
+    # EPCL (empty pre-cool automation)
 
 
 class Valve(MercuryChannel, Drivable):
@@ -76,7 +75,19 @@ class Valve(MercuryChannel, Drivable):
         self.read_status()
 
     def read_value(self):
-        return self.query('VALV:SIG:STATE', open_close)
+        pos = self.query('VALV:SIG:STATE', open_close)
+        if pos == self.target:
+            self.status = IDLE, ''
+            self._try_count = 0
+            self.setFastPoll(False)
+        elif self._try_count <= 7:  # odd number: last try is previous position
+            # toggle new/previous position until success or too many tries
+            self.change('VALV:SIG:STATE', pos if self._try_count % 2 else self.target, open_close)
+            self._try_count += 1
+            self.status = BUSY, 'opening' if self.target else 'closing'
+        else:
+            self.status = ERROR, 'can not %s valve' % self.target.name
+        return pos
 
     def read_status(self):
         pos = self.read_value()