Motor Operated valves 1

[proelect8717]

dear all,

I am now conforted to maintenance and re conditioning of various type of old and new MOVs (Motor Operated valves). I have no past experience with these devices. Can i get some good technical literature, books on them how they work, types, troubleshooting etc etc.

I am sorry, if there already exists a thread on Motor operated valves.

Please help.

Thank you.

 

[crshears]

Hi proelect8717,

I just used the search function at the top of the eng-tips page [NOT the one that says "Google Custom Search" but the one to the right of that] looking for the search string 'motor operated valve' - at least the first half-dozen or so of the results looked promising, at least to me.

Can i get some good technical literature, books on them how they work, types, troubleshooting etc etc.

There's kind of a wide answer to this one, and what follows will barely begin to scratch the surface of the topic...

The smallest MOV I ever saw was in someone's apartment as part of the hot-water-type heating system; a centre-contact thermostat fed 24 VAC to a pair of wires which led to the ball valve. The valve body was at the bottom; next was a geared-down drive motor, and on top two notched wheels were mounted on the valve spindle. One wheel had notches at 90° and 270°, and the other had notches @ 0° & 180°. Each wheel had a limit switch attached to it; the wires from the thermostat attached one each to the limit switches, while the common side of the limit switches led to the valve drive motor.

With the valve shut, on a call for heat, thermostat would toggle power down one wire; motor would run until valve had rotated 90°, at which point the limit switch in that wire would open the circuit and the motor would stop, leaving valve in open position. When thermostat was satisfied it would toggle power supply to the other wire and the motor would run until it had rotated another 90°, at which poin the other limit switch would open and the motor would again stop, leaving the valve closed.

Simplicity itself.

From this point on, motor-operated valves just get bigger and/or more complicated.

Based on my admittedly limited operating background, the parameters to be considered when it comes to motor operated valves include but are not limited to:

Medium controlled: almost exclusively fluids, meaning either liquids or gases.

Flow volume: low, medium, high

Flow regimes: [a] valve normally either fully closed or wide open, meaning not designed for throttling purposes, or designed to be capable of continuous operation at any position between fully shut and fully open without the valve sustaining damage. These criteria have more to do with the valve and less with its actuator...but valve and actuator characteristics often reflect on each other, so don't make the mistake of concentrating exclusively on the actuator while ignoring the valve.

Temperature of controlled medium: low, moderate, high

Operating Pressure: low, medium, high

Normal pressure differential expected across the valve - - you guessed it: low, moderate, high

Size: all the way from tiny to huge

Actuator and valve spindle rotation: unidrectional and reversing

Duty cycle / expected frequency of operation and duration of each operation: [a] hardly ever operated, but often including the proviso that when called upon, must operate reliably; operated once to several times per week, or [c] per day or [d] per hour

Power supply: DC, fixed frequency AC and, in specialized applications, variable frequency AC

Control schemes: manual, meaning by an operator's hand on a pistol-grip switch or finger on a pushbutton; automatic with optional manual control; fully automatic

Means of limiting travel of valve: straightforward limit switches or the more elegant torque-limiting controllers, which often do a better job of fully closing valves in severe duty applications, such as high-pressure steam line drain valves

And finally, one of our contributors uses the tag line: "Quality, qunatity, and price: pick two."

Hope this helps.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[crshears]

Also, have a look at the Valve Engineering Forum @

http://www.eng-tips.com/threadminder.cfm?pid=408

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[squeeky]

Look at teh Auma valve website. They go from very simple to highly complex.

 

[ScottyUK]

Check out Rotork too, arguably the best-known (?) manufacturer.

 

[crshears]

Thanks, Scotty! I'd pretty well forgotten about Rotork valves, as it's been a few years since I had to operate them...the other major maker is [was?] Limitorque.

What I do recall, though, was that both Rotorks and Limitorques were used as turbine drain valves, and both needed to be monitored regularly to ensure that the limit switches on the strain mechanism were properly set, since it was this setting that ensured the valves would seat fully when called upon to do so. The duty of these valves was quite severe, and if the valve continued to pass steam due to not being fully shut, erosion of the valve would occur in short order due to wire-drawing by the steam, which would more frequently cut a notch in either the disc or the seat rather than simply eroding these evenly all the way around.

It was part of my job as an auxiliary plant operator to check all the turbine drain valves shut once the turbine-boiler operator in the control room had selected them to the shut position, and promptly fully close manually any valves that had not fully shut on their own. Any repeated failure of such a valve to shut fully was reported to the electricians, who would adjust the limit swiches as required to remedy the defect. Prompt attention to this was required, since the longer passing and hence wire-drawing was allowed to go on the higher the likelihood that the seat or disc would become so badly cut that it was impossible to get the valve fully shut at all, which meant a valve rebuild by the mechanical department during the next major shutdown and overhaul...

Another thing we operators did was to apply adequate amounts of a graphite-based high-temperature lubricating paste such as Never-Seez to the valve stems when the unit was shut down so that when the valve was called upon to close during the next unit start-up the paste would be carried along the stem and coat the surfaces of the valve packing, thereby maintaining a uniform torque requirement on the valve. The motor mechanism's torque limiting element could not tell whether the torque it was applying was being used to close the valve or overcome the friction of dry or overly tight packing, and failure by the operators perform this simple but important task could alther the valve's performance characteristics significantly.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[ScottyUK]

Rotork and Limitorque types can be set to either operate on torque or position as you clearly know. Getting the wrong option for the valve in question would be an operational nightmare. I'm not familiar with noticeable drift in limit switch positions on the types we have, which covers the majority of sizes from both manufacturers and across a forty year timeframe. Our biggest problem is the bronze drive bushes wearing out on Rotorks.

 

[electricpete]

You can download detailed maintenance recommendations / procedures for Limitorque Actuators here:

http://www.epri.com/search/Pages/re...or the Limitorque Model SMB-00 Valve Actuator

=====================================
(2B)+(2B)' ?

 

[crshears]

Rotork and Limitorque types can be set to either operate on torque or position as you clearly know.

Actually, I did not know that!

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[ScottyUK]

:-D

Ball, butterfly and most (all?) gate valves typically seat on position, globes seat on torque. If you think about how the valve is built internally and how the sealing arrangement is designed to operate it probably explains itself.

 

[crshears]

If you think about how the valve is built internally and how the sealing arrangement is designed to operate it probably explains itself.

I did, and you're right; it does

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]