Patent ID: 7828008

Claim:
A fault-tolerant method for opening, closing and partial stroke testing (PST) of a critical valve using a 2 out of 4 (2oo4) solenoid valve arrangement comprising the steps of: a. configuring a 2oo4 solenoid valve arrangement with a first leg having a first solenoid valve and a second solenoid valve in series and a second leg having a third solenoid valve and a fourth solenoid valve in series, wherein the first leg is parallel to the second leg providing two redundant supply paths and two redundant vent paths, for selectively supplying gas to and venting gas from the critical valve; b. flowing at least a portion of a gas stream from a supply input through the first leg and at least a portion of the gas stream from the supply input through the second leg; c. opening the critical valve with the gas from either of the two redundant supply paths; d. determining a calibration time interval by closing the critical valve to a preset partial stroke testing position and recording a first elapsed time under process operating conditions, wherein the first elapsed time is the time elapsed during the closing of the critical valve to a preset partial stroke testing position; e. verifying the two streams of gas are providing required operating pressure; f. determining a measured PST time interval by closing the critical valve to the preset partial stroke testing position and recording a second elapsed time under process operating conditions, wherein the second elapsed time is the time elapsed during the closing of the critical valve to a preset partial stroke testing position under process operating conditions after the first elapsed time has been recorded; g. using partial stroke testing logic to monitor the measured PST time interval to ensure the critical valve does not exceed a maximum time limit needed for closing the critical valve; h. comparing the measured PST time interval to the calibration time interval to determine if the measured PST time interval does not exceed the maximum time limit needed for closing the critical valve and the critical valve passes the partial stroke testing; and i. acquiring data for each of the solenoid valves, wherein the first solenoid valve is in communication with a first pressure sensor, the second solenoid valve is in communication with a second pressure sensor, the third solenoid valve is in communication with a third pressure sensor, and the fourth solenoid valve is in communication with a fourth pressure sensor, and wherein the partial stroke testing logic selectively opens or closes the solenoid valves depending on the acquired data.