Motor Operated Valve (MOV)

Something (bacterial buildup or lime precipitation in the line?) may have been stuck to the ball, or there may have been dirt or a mechanical obstruction on the actuator. The actuator drive was not strong enough to overcome it, but the operator was.

Another possibility is lubrication breakdown in the actuator mechanism. Manually forcing it redistributed the lubricant so it will work for a while. You can check for this by comparing actuator current or manual operating force with other similar units.

The next step is to determine the most probable cause and take steps to prevent a recurrence.

check the control circuit , limit switch, or contactor contacts

make some maintenance and overhaul to see the conditions may be something stuck there

Yes, my first suspect would be the limit switches. If they do not indicate the position of the valve correctly, the Motor Operator will not respond to a command. it is intended as a fail safe against accidentally giving the MOV an Open and Close command at the same time, or to prevent over travel. But if the switches fail or the contacts corrode, the "fail safe" mode is to do disable the motor operation.

Is this valve placed in oil service, if so the reason may be oil degradation leading to sludge formation across valve and other such surfaces. You need to get your oil checked for oxidation and possibly get it electrostatically cleaned.

Has somebody look at the limit and torque switches status when electrical command doesn't go?

The opening and closing are done always in the same system conditions? If MOV actuator is not properly adjusted, it can operate under no load condition (no delta P) and fail if delta P is present.

The globe valve is balanced type? What's the flow direction?

I find difficult for a globe valve to get stuck everyday by any deposit type.

What type of fluid can build in just one day a deposit which stucks the disc into the seat in such a way as to block a motor operator?

A simple way to see if it's a problem with pressure or just switches misadjustment is to measure the motor current while trying to remote or local actuating the valve. If the current is high (locked rotor) then is a valve problem (pressure). If no current is present then there is a problem with switches adjustment.

By the way, which motor operator trademark is?

Kind regards

An MOV not far from here displayed a similar phenomenon. The cause was eventually traced to the magnetism from the steel non-return valve nearby being sufficiently strong to operate the reed switch that prevented the device from motoring.

First impressions on reading could be the limit switches set up incorrectly or even control wire connections not connected tightly therefore intermittent fault also broken wire, may arise again if this not checked, but if now operating would suspect that unit had seized & the operation of MOV freed off,would still check out control cct to make sure!

Dear Giri,

I too would vote for the limit switch scenario as being 'top of the list' of possibles.

Remember that to start the valve opening it is the opposite end of travel switch which is suspect as this is the device which prevented the actuator going 'over limit' when it last ran open properly,(as against the one it will be currently at). Depending on the environment a bit of stiction can easily cause this problem and usually a squirt of WD-40 or similar works wonders.

If you have a population of these valve actuators it would be as well to service them all whist dealing with this issue.

Good luck,

Massey.

Globe valves (especially motorized globe ) hardly ever stick as long as they are installed with correct flow and stroked every once in awhile. I have seen globe valves stick when installed backwards with the flow because the flow would push against the side of the globe/stem instead of against the bottom and this would in-turn cause it to bend and then stick. I don't think this is your problem though if it works some of the time.

All of the motor valves I have seen the gear reduction gives more torque than most men have unless your guy was using a long valve wrench to help open the valve. You don't tell us what size valve it is or the HP of the motor and if it has a reduction gear so It is hard to say how much torque or HP it would take to close it. I would say it is a near shorted wire, loose connection, bad limits, or some other electrical problem if I had to guess because of the fact that the problem is not continuous.

Since I'm more suspicious than most I could tell you that enough out of specs overpressure is a possible reason for a globe valve to refuse to open (but not to refuse to close) as of course is infrequent operation with depositing fluids. All this providing the motor voltage is within specs too.