Samson 3730 Series Operating Instructions

EB 8389-1S EN 73
Partial stroke test (PST)
12 Partial stroke test (PST)
The partial stroke test (PST) is particularly
suitable for the status-oriented detection of
malfunctions in pneumatic shut-off valves. As
a result, the probability of failure on demand
(PFD) can be reduced and it may be possible
to extend maintenance intervals.
A shut-off valve normally in its end position
can be prevented from seizing up or getting
jammed. The breakaway torque must be
overcome when the plug starts to move out
of its open position. This breakaway torque
depends on the seal, deposits on the seat
and plug, the process medium and friction in
the valve trim. After the breakaway torque
has been overcome, it can be assumed that
the valve is able to completely close. Record-
ing the test results additionally allows an
analysis of the dynamic control response.
The partial stroke test can be performed
once (test immediately started) or, with an
on/off valve in automatic mode, regularly
(time-controlled), provided the start condi-
tions are met (see u Table 4):
− A control valve is in the manual mode.
− An on/off valve is in the manual or auto-
matic mode. In automatic mode, the test
is only started when the Set point w is
greater than the 'Fail-safe action limit'
(Code49 - h2).
The following listed parameters are activated
while the partial stroke test is being per-
formed:
− Characteristic selection (Code 20): Linear
− Required transit time OPEN (Code 21):
Variable
− Required transit time CLOSED (Code 22):
Variable
Fig. 17: Diagnostics > Monitoring/tests > Dynamic tests > Partial stroke test (PST)

Samson 3730 Series Specifications

General

Brand	Samson
Model	3730 Series
Category	Valve Positioners
Language	English