d) Cam
i) If cam nut and locking screw are not correctly inserted the positioner will not work
correctly, generally resulting in the cam slipping and a small input change will
equal a full stroking of the actuator. Make sure that the locking screw is all the
way out before you tighten the cam nut; then secure the locking screw
(the cam nut is the first lock – the screw is the second lock). The cam pictured
below is INCORRECT, and will result in cam slipping and full stroking of the
actuator on small input changes.
ii) Make sure that the Positioner action (direct acting or reverse
acting) corresponds with the cam. A “D” or an “R” can be
found on the cam to indicate direction of cam rotation.
(1) An easy way to check this is to remove the cover of the
positioner and watch the rotation to ensure that cam
placement is correct.
e) Spool Valve
i) Dirty air can cause particulates to cause “sticking” and prevent the positioner
from working correctly. (see below hunting)
(1) Remove the spool valve and blow out with air. If air is not available wipe down with cloth.
Once cleaned the spool piece should slide very easily in its housing. Place spool valve back into
positioner making sure that the slotted top of the spool piece is connected
correctly on the balance arm.
f) Gauge Plugs
i) All gauge plugs or gauges must be secure (no air leaks!!). If the
plugs or gauges are not properly tightened air can leak causing the
positioner not to respond to input signal. Note: gauges are very
useful when trouble shooting a positioner. This helps “inspect” the
air flow through the positioner as well as the I/P output. Three 0-160
psi gauges are used for the supply (S port) and two output ports
(C+ and C-). A 0-30 psi gauge is used for the I/P output.
g) Mounting
i) Rotary
