Instruction Manual

Detailed Setup
September 2013
4-23
Table 4-10. Estimates for Partial Stroke Pressure Limits
Actuator Style Relay Type
Zero Power
Condition
PST Starting Point Partial Stroke Pressure Limit
Spring and
Diaphragm
A or C
Closed
Open Pmin − 0.25 * (Bench Set High − Bench Set Low)
Closed Pmax + 0.25 * (Bench Set High − Bench Set Low)
Open
Open Pmax + 0.25 * (Bench Set High − Bench Set Low)
Closed Pmin − 0.25 * (Bench Set High − Bench Set Low)
B
Closed
Open Pmax + 0.25 * (Bench Set High − Bench Set Low)
Closed Pmin − 0.25 * (Bench Set High − Bench Set Low)
Open
Open Pmin − 0.25 * (Bench Set High − Bench Set Low)
Closed Pmax + 0.25 * (Bench Set High − Bench Set Low)
Single-Acting Piston
A or C
Closed
Open 0.5 * Pmin
Closed Pmax + 0.5 * (Psupply − Pmax)
Open
Open Pmax + 0.5 * (Psupply − Pmax)
Closed 0.5 * Pmin
B
Closed
Open Pmax + 0.5 * (Psupply − Pmax)
Closed 0.5 * Pmin
Open
Open 0.5 * Pmin
Closed Pmax + 0.5 * (Psupply − Pmax)
Double-Acting Piston A
Closed
Open Pmin − 0.5 * (Psupply + Pmin)
Closed Pmax + 0.5 * (Psupply − Pmax)
Open
Open Pmax + 0.5 * (Psupply − Pmax)
Closed Pmin − 0.5 * (Psupply + Pmin)
Valve Stuck Alert
CAUTION
If a valve stuck alert is active, there
may be potential energy stored in the
valve and actuator assembly. Sudden
release of this energy may cause the
valve to suddenly open or close,
resulting in equipment damage.
While performing the partial stroke test, even if the
valve sticks, the digital valve controller will not fully
exhaust or fill the actuator pressure in its attempt to
complete the partial stroke. Rather, the instrument will
abort the test and issue an alert. It is recommended
that the Travel Deviation alert be enabled and
configured.
The Valve Stuck alert will be generated either by the
Travel Deviation alert (the difference between
expected and actual travel exceeds the level defined
in the deviation alert), or if the actuator pressure
reaches the Partial Stroke pressure limit. If the Travel
Deviation alert is not configured, then the Partial
Stroke pressure limit will abort the test and cause the
Valve Stuck alert.
If the valve is stuck and only the Travel Deviation alert
is enabled (without specifying partial stroke pressure
limit) the Valve Stuck alert will still be generated and
the test will be aborted.
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