Main control gives a full close signal, the valve is closed at 15%, and it does not close in place.

1.Fault Type

Main control gives full close signal, valve closes at 15, not closing in place

2. Instrument Type 

Masoneilan control valve

3. Valve Information 

Manufacturer: U.S.oneilan

Tag: 1FV-3006

Model: M:35-35502-8013-7-4HW080

Flange Standard: DN50

Temperature: 212℃

Fault Location: FO

Pressure: 20-100 psi

Valve Body Material: Stainless Steel

4. Operating Conditions

To the Venturi Scrubber Water Flow Control Valve

Medium: Black Water

Pressure: 4.5Mpa

Temperature: 212℃

5.ault Phenomenon

The main control room gives 25% to 17FV-3006, the valve opens to 25%, a signal of 50%, the valve opens to 50%, gives a signal of 75%, the valve opens to 75%, gives a of 100%, the valve opens to 100%, when the close signal is given out 0%, the field valve stays at about 1%, not closing in place.

6. Safety Measures Before Handling

（1）Contact with the process to ensure the cause of the fault. 

（2 ）Handle the relevant maintenance work ticket, fill in the risk identification in the work ticket clearly according to the actual situation on site, and do a good job of relevant safety protection measures and relevant safety protection equipment. 

（3）17FV-3006 valve is on the 2nd floor of the slag water, because the platform a grid shape, so the maintenance should be done on the platform with aluminum skin or non-perforated things, to prevent tools or valve accessories and other objects from falling during. 4. Before maintenance, prepare the corresponding maintenance tools and wear relevant labor protection supplies.

7. Fault Cause Analysis and Judgment

（1） The source pressure is too low. 

（2）The positioner does not move or the positioner is not energized. 

（3） The air pressure reducing valve is damaged blocked, the air passage is not unobstructed, and the valve diaphragm leaks. 

（4）The signal connection terminal is loose or not powered. 

（5） The valve core is stuck, and there is debris in the pipeline.

8. Effective Fault Handling Methods

Fault Judgment:

（1）Check the valve gas source pressure on site 0.42MPa, the gas source pressure is normal. 

（2）Open the Masoneilan positioner cover no looseness in the wiring, check the voltage with a multimeter 23.5V is normal. 

（3） Use a walkie-talkie to the main control room, let the main control room give a 50% open signal, and then give a 0% close signal, the valve opens to 50% closes to about 15%, the pressure reducing valve gas source output is normal, the signal output is normal, and there is no leakage in the valve diaphragm 

（4）Notify the main control room to give 25%, 50%, 75%..... back and forth, when valve closes at 15%, it is found that the valve core has a slight tremor, and it is judged that the valve core of the valve may be scaling, in the valve not closing in place.

Handling Method:

Turn off the valve gas source, remove the power supply, connect the valve with a gas source hose manually operate the valve, the valve can be closed to 10%. Disassemble the valve accessories, then disassemble the valve, clean the valve core scaling with water and fine cloth, then manually operate the valve with a gas source hose, the valve closes in place, reassemble the valve, install the valve accessories, connect the gas pipe and signal line, and adjust the valve normally.

9. Fault Prevention Measures and Improvements

Pay attention to the rain and water proof of valves and accessories during patrol inspection, prevent the valve positioner from getting water, when the valve has a fault, it can effectively rule out the interference of valve accessories and other faults, and the inspection efficiency. When conditions permit, the process personnel can be allowed to actuate the valve on time, to avoid the valve from not moving for a long time and scaling, the normal operation of the valve.

10. Fault handling experience

When dealing with faults, it is necessary to be clear about the medium flowing through the valve, the valve temperature, valve pressure, and take corresponding protective measures. Analyze the possible faults according to the position of the valve and the medium flowing through it, and accurately judge the fault