Fluid handling – With indicator – register – recorder – alarm or inspection means – Plural
Patent
1998-12-04
2000-10-17
Rivell, John
Fluid handling
With indicator, register, recorder, alarm or inspection means
Plural
137554, 73168, F16K 3700, G01M 1900
Patent
active
061316091
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns a method for surveying the condition of a control valve apparatus, the position of which is adjusted by means of an actuator controlled by an electropneumatic positioner and operated by means of pressure medium, whereby the operation of the valve is monitored by sensors that during the valve operation read at certain reading intervals the readings at least from the control signal of the valve, the input pressure of the positioner, the difference between the input and output pressure of the actuator, and the position of the valve, and the fault causing the deviating reading is located by means of a microprocessor by using the readings given by the sensors and deduction rules stored in the microprocessor.
The invention also concerns a control valve apparatus comprising a valve, an actuator driven by means of a cylinder-piston device, and an electropneumatic positioner, sensors for monitoring at least the control signal of the valve, the input pressure of the positioner, the difference between the input and output pressure of the actuator, and the valve position as well as means for storing the information received from the sensors and the deduction rules to be used for locating a fault and for processing the information received from the sensors in accordance with these rules.
BACKGROUND ART
A control valve and its operation are known in the art and there is no need to describe it in more detail in this connection. The valve can be a quarter-rotational or a linear valve, said designations describing the moving direction of the closing element of the valve in the controlling situation. A quarter-rotational valve can be e.g. a ball valve or a butterfly valve. Examples of a ball valve have been described e.g. in U.S. Pat. No. 4,747,578. The valve is operated by means of an actuator that turns the turning shaft of the closing element between the closed and the opened position. The actuator can be driven by means of a cylinder piston device controlled by a pilot valve. This pilot valve is located in the positioner of the control valve. The positioner is a device for amplifying the control signal into the operation pressure of the pneumatic actuator. In the electropneumatic positioner, the electric signal is amplified into the pneumatic operation pressure. The positioner, by means of a feed-back element, also positions the valve to correspond to the control signal.
The diagnostics of control valves equipped with a pneumatic actuator is in general based on tests performed on the control valves, such as step-function response and hysteresis tests. A requirement for performing the tests is that the process is stopped, whereby the tests are performed at site of the valves. The testing equipment often also includes complicated sensors that can make the testing on the field complicated (U.S. Pat. No. 5,197,328). This is so called off-line diagnostics.
The diagnostics can also be performed on-line, whereby the positioner of the control valve monitors e.g. the position message of the valve and gives an alert if the position message deviates too much from the value presupposed by the control system. Part of the on-line diagnostics are also the operation counters of the valve that give an alert when the number of the operations exceeds a certain predetermined limit. This diagnostics system, however, does not include any deduction procedure by which the faults could be located. In both of the U.S. Pat. No. 5,329,465 and U.S. Pat. No. 4,694,390, valves have been described, in the control system of which separate measuring sensors are used. The inventions described in the publications concern an on-off regulation of the valve, not continuous controlling.
In the system according to U.S. Pat. No. 5,329,465, sensors are used for condition surveying of the valve and for collecting historical data for the data base. The fault analysis is made by comparing the measured values with the values collected earlier for the data base. The position of the valve is not adjusted continuously
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Metso Mika
Pyotsia Jouni
Neles Controls Oy
Rivell John
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