Diagnostic apparatus and method for fluid control valves

• US 4,976,144 A
• Filed: 04/10/1990
• Issued: 12/11/1990
• Est. Priority Date: 08/25/1988
• Status: Expired due to Term

• Current Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Original Assignee: Fisher Controls International LLC (Emerson Electric Company)
• Inventors: Fitzgerald, William V.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): GUTIERREZ, DIEGO F
• Application Number:
  US07/512,095
• Time in Patent Office: 245 Days
• Field of Search: 73/168, 73/37, 73/812, 73/865.6, 73/4 R, 73/862.32, 73/9, 137/487.5, 364/558, 364/550, 364/556
• US Class Current: 73/168
• CPC Class Codes: F16K 37/0083 by measuring valve parameters
• CPC Class Codes: F16K 37/0091 by measuring fluid parameters
• CPC Class Codes: Y10T 137/7761 Electrically actuated valve

Abstract

Apparatus and method for diagnostically testing and determining the operating condition of a pneumatically operated valve. A diagnostic controller is connected to a valve actuator assembly so that diaphragm pressure and valve plug movement among other inputs can be sensed while the valve actuator assembly is stroked through a test operation cycle. The sensor output signals are then used in selected graphical plots to provide information which can be analyzed to indicate the condition of the valve in such areas as spring adjustment, stroking time, valve travel, stem friction, seat load, and positioner and transducer calibration.

Claims

1. Apparatus for diagnostically testing and determining the operating condition of a pneumatically operated fluid control valve, said valve having a pneumatic actuator interconnected to a valve flow control member for moving the flow control member between respective closed and open valve positions with respect to a valve seat, and a variable pneumatic pressure line connected to a valve positioner providing a variable pneumatic pressure output to the input of the pneumatic actuator for operating said valve in a test operation cycle defined by moving the flow control member along at least a portion of the movement between said respective closed and open valve positions, said apparatus comprising:

first transducer means for sensing the pneumatic pressure at the input of the pneumatic actuator during said test operation cycle and providing a corresponding first output signal for flow control member movements encompassing the fully closed valve position wherein said flow control member is seated on the valve seat;

second transducer means for sensing the movement of the flow control member during said test operation cycle, and providing a second output signal for flow control member movements encompassing the fully closed valve position;

signal processing means responsive to said first and second output signals for providing valve diagnostic data corresponding to variations in the pneumatic pressure at the input to the pneumatic actuator as a function of the movement of the flow control member during a portion of said test operation cycle corresponding to flow control member movements encompassing the fully closed valve position; and

output display means coupled to said signal processing means for displaying said valve diagnostic data and thereby enabling determination of valve seat load values for said valve under test;

said output display means including means for displaying a substantially linear relationship in said pneumatic pressure as a function of flow control member travel during said test operation cycle and displaying at least two pneumatic pressure values at the end of the test operation cycle corresponding to closing of the valve as the flow control member initially contacts the valve seat and is then totally seated against the valve seat, said two pneumatic pressure values including a pressure value (1) at the point in flow control member travel where the pneumatic pressure abruptly changes from said linear relationship and a pressure value (2) at the point in the flow control member travel where the maximum pneumatic pressure value is reached and the pressure abruptly changes as the flow control member travel direction is reversed.

2. A method for diagnostically testing and determining the operating condition of a pneumatically operated fluid control valve having a valve actuator connected to a valve flow control member for movement between respective closed and open valve positions with respect to a valve seat, comprising the steps of:

providing a pressure sensor to sense varying pressure at the input of the valve actuator;

providing a position sensor to sense movement of the flow control member;

providing controlled variable pneumatic pressure to the input of the valve actuator to operate the valve in a test operation cycle defined by moving the flow control member along at least a portion of the movement between said respective closed and open valve positions;

obtaining a first signal from the pressure sensor corresponding to varying pressure at the valve actuator input during the test operation cycle for flow control member movements encompassing the fully closed valve position wherein said flow control member is seated on the valve seat;

obtaining a second signal from the position sensor corresponding to movement of the flow control member during the test operation cycle for flow control member movements encompassing the fully closed valve position;

processing said first and second signals to derive valve diagnostic data representing the variation in pressure at the valve actuator input as a function of movement of the flow control member during the test operation cycle corresponding to flow control member movements encompassing the fully closed valve position; and

displaying said valve diagnositc data for enabling determination of valve seat load values for said valve under test;

including the steps of displaying at least two pneumatic pressure values at the end of the test operation cycle corresponding to closing of the valve as the flow control member initially contacts the valve seat and is then totally seated against the valve seat, said two pneumatic pressure values including a pressure value (1) at the first point in flow control member travel where the pneumatic pressure initally abruptyl changes in value at the end of the test operation cycle and a pressure value (2) at the second point in the continued travel of the flow control member where the maximum pneumatic pressure value is reached and the pressure again abruptly changes as the flow control member travel direction is reversed.

3. Apparatus for diagnostically testing and determining the operating condition of a pneumatically operated valve, said valve having a pneumatic actuator driving an interconnected actuator stem, valve stem, and valve plug for moving the valve plug into and out of sealing engagement with the valve seat corresponding to respective closed and open valve positions, and a variable pneumatic pressure line connected to a valve positioner providing a variable pneumatic pressure output to the input of the pneumatic actuator for operating said valve in a test operation cycle defined by moving the valve plug from a fully open position to a fully closed position and from said fully closed position to a fully open position, said apparatus comprising:

first transducer means for sensing the pneumatic pressure at the input of the pneumatic actuator during said test operation cycle and providing a corresponding first output signal (ch.5);

second transducer means for sensing the movement of the valve plug during said test operation cycle, and providng a second output signal (ch.6);

signal processing means responsive to said first and second output signals for providing valve diagnostic data corresponding to variations in the pneumatic pressure at the input to the pneumatic actuator as a function of the movement of the valve plug during said test operation cycle;

third transducer means for sensing the pneumatic pressure at the variable pneumatic pressure line during said test operation cycle and providing a corresponding third output signal (ch.3); and

wherein said signal processing means is responsive to said second and third output signals for providing valve diagnostic data corresponding to movement of the valve plug (ch.6) as a function of variations in said variable pneumatic pressure line (ch.3) during said test operation cycle.

4. Apparatus according to claim 3, including a current to pressure transducer having a variable control current signal input (ch.1) and a variable pneumatic pressure output coupled to the variable pneumatic pressure line connected to the valve positioner;

and

wherein said signal processing means is responsive to said variable control current signal and to said third output signal for providing valve diagnostic data corresponding to variations in said variable pneumatic pressure line connected to the valve positioner (ch.3) as a function of said variable control signal (ch.1) during said test operation cycle.

5. Apparatus according to claim 4, including display means for displaying said valve diagnostic data and enabling determination of at least valve friction values, valve seat load values, valve positioner calibration values, and current to pressure transducer calibration values for said valve under test.