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User Instructions - Logix® 520MD+ Series Digital Positioner

FCD LGENIM0105-00

Field Trial Version – Printed October 28, 2011

6 TUBING

After mounting has been completed, tube the positioner to
the actuator using the appropriate compression fitting
connectors.

6.1

Determine Air Action

The  port  labeled  “Y1”  delivers  air  when  an  air  supply  is
present  and  the  relay  is  energized.    (For  positioners  with
double  acting  relays,  this  is  port  A.    For  positioners  with
single acting relays, this is port B.)  Typically, the port labeled
“Y1”  should  be  tubed  to  the  pneumatic  side  of  the  actuator
(the side that would result in the air compressing the actuator
spring).    When  tubed  this  way,  the  spring  is  designed  to
return  the  valve  to  the  fail  safe  state  should  supply  air  or
power to the unit fail.

Tube  the  port  labeled  “Y1”  to  the  side  of  the  actuator  that
must  receive  air  to  begin  moving  away  from  the  fail  safe
state.

If  air  from  “Y1”  should  open  the  valve,  set  the  Air  Action
configuration  switch  on  the  positioner  to  Air-to-Open,
otherwise set it to Air-to-Close.

The  Air-to-Open  and  Air-to-Close  selection  is determined  by
the  actuator  tubing,  not  the  software.  When  air  action
selection is made during configuration, the selection tells the
control which way the actuator has been tubed.

If the valve is double acting, port the valve labeled “Y2” to the
other side of the actuator.

DANGER: Proper tubing orientation is critical for the

positioner to function correctly and have the proper failure
mode.

Example: Linear Double-Acting Actuators

For  a  linear  air-to-open  actuator,  the  “Y1”  port  of  the
positioner is tubed to the bottom side of the actuator (closest
to  the  valve).  The  “Y2”  port  of  the  positioner  is  tubed  to  the
top side of the actuator. For a linear air-to-close actuator the
above configuration is reversed.

Example: Rotary Double-acting Actuators

For a rotary actuator, the “Y1” port of the positioner manifold
is  tubed  to  the  bottom  side  of  the  actuator.  The  “Y2”  port  of
the  positioner  manifold  is  tubed  to  the  top  side  of  the
actuator. This tubing convention is followed regardless of air
action.  On  rotary  actuators,  the  transfer  case  orientation
determines the air action.

Example: Single-acting Actuators

For  single-acting  actuators,  the  “Y1”  port  is  always  tubed  to
the pneumatic side of the actuator regardless of air action. If
a  double  acting  -  spool  style  relay  is  installed  in  the
positioner, plug port B (Y2). If a  single acting - poppet style
relay  is installed,  port  A can  be  plugged  or  may  be  used for
purging. See Purging Single Acting Actuators below.

6.2

Connect Supply Port

The  positioner  ports  are  threaded  with  either  G  ¼  or  ¼
NPTF as indicated on the housing.

In  order  to  maintain  the  recommended  air  quality,  a
coalescing filter should always be installed in the supply gas
line.    An  air  filter  is  highly  recommended  for  all  applications
where  dirty  air  is  a  possibility.  The  positioner  passage  ways
are  equipped  with  small  filters,  which  remove  medium  and

coarse  size  dirt  from  the  pressurized  air.  If  necessary,  they
are easily accessible for cleaning.

A  supply  regulator  is  recommended  if  the  customer  will  be
using the diagnostic features of the Logix 520MD+ but is not
required. In applications where the supply pressure is higher
than  the  maximum  actuator  pressure  rating  a  supply
regulator  is  required  to  lower  the  pressure  to  the  actuator’s
maximum rating.

6.3

Purging Single Acting Actuators

Purging  allows  the  non-pressurized  side  of  a  single  acting
actuator  to  fill  with  exhaust  gas  instead  of  atmospheric  air.
This  configuration  helps  prevent  corrosion  of  actuator
components  in  harsh  environments.    When  a  single  acting
relay  is  used,  a  special  procedure  can  be  performed  to
configure  the  positioner  to  purge  properly  using  port  A.
Contact  your  local  Field  Service  Technician  for  more
information regarding the purging option.

6.4

Vented Design

A standard Logix 520MD+ positioner is vented directly to the
atmosphere.  When  supply  air  is  substituted  with  sweet
natural  gas,  piping  must  be  used  to  route  the  exhausted
natural gas to a safe environment.

The  housing  chamber  exhaust  port  is  located  on  the
backside  of  the  positioner.    The  actuator  exhaust  port  is
located  on  the  bottom  of  the  positioner.    Both  ports  are
tapped with either ¼ NPTF or G ¼ threads and covered with
a  protective  cap.    To  control  vented  gas,  remove  the  caps
and connect the necessary tubing/piping to these ports. See
Figure 5:  Exhaust Vents.

Figure 5: Exhaust Vents

This  piping  system  may  cause  some  positioner  back
pressure.  Back pressure in the housing chamber is from the
modulator  and  regulator.    Back  pressure  in the exhaust  port
is from the actuator.

The  maximum  allowable  back  pressure  from  the  housing
chamber is 0.14 barg (2.0 PSIG).  For flow rates, see section
3.2 Air Supply.

The maximum allowable back pressure from the exhaust port
is  0.55  barg  (8.0  PSIG)  for  double  acting  relays  and  is  0.14
barg  (2.0  PSIG)  for  single  acting  relays.    Higher  pressure
may result in decreased performance.  For output flow rates,
see section 3.3 Pneumatic Output.