Stepper motor valves to manage fluid or water flow?

[schnell]

Do you know of any companies who use mains powered equipment which controls stepper motor valves to manage fluid or water flow?

 

[gerhardl]

'Mains'? - could you please give details on size, pressure and flow?

 

[moltenmetal]

Your question is too vague to answer. Be more specific and maybe we can help.

 

[btrueblood]

Short answer is no. Steppers are DC motors, and typically operate at "low" voltage, i.e. 48 vdc or less. So something, typically an AC-DC power supply and switching transistors, is interposed between mains and stepper motor.

We do use 110-volt "mains" power to power actuators for large ball valves on our test stands. And lower voltage (typ. 24 volts) for the stepper motors on smaller valves we build.

Many companies manufacture electric motor actuated valves, or servo actuators that can be adapted to valves, and many of the motors are steppers, at least in smaller sizes. Google or otherwise search some of the terms in that last paragraph and you should find a wealth of manufacturers.

 

[schnell]

Hi,

Please may i explain myself more sufficiently....


I am referring to any equipment whatsoever which uses stepper motors to control valves....where the primary power source for the stepper motors is mains electricity.

...i appreciate that the mains will be converted to a lower voltage by , for example, an offline switch mode power supply.

I am interested to know what these companies do when the mains suddenly fails, and the stepper motor driven valves are fully open.

....because there is no energy available to close the valves.

The "obvious" way around this woul dbe to use big capacitors across the stepper motor voltage rail....

...but the problem is that such capacitors have to be pretty big, and PWM controllers in SMPS's do not handle such circuits well, because they tend to go into "auto-restart" mode because the output reaches regulation value too slowly (due to the big capacitors)

an alternative power fail energy source would be rechargable batteries, but these are expensive and have short lifetimes, and need constant trickle charging.

 

[rmw]

I know of one company that uses stepper motors with 110VAC power to the actuator. I saw their actuator in a Fisher catalog yesterday. Their name used to be Jordan Controls and may now go under the name Rotorque. I think the actuator is a MV 1020.

One feature (good sometimes, bad others) is that an electric actuator fails in place. One way around that is to provide a battery back up to drive the valve shut upon main power failure.

rmw

 

[moltenmetal]

Stepper motor control valves are common and made by numerous vendors including Hass Industries.

Stepper motor control valves fail in last position, not open or closed. This is a problem which can be solved by the same means that you use to solve it with pneumatic control valves, which ALSO should not be relied upon to seal tight in their failure position: you put an actuated, tight sealing on-off type valve in series to handle the failure position. A pilot-operated solenoid valve will do this just fine up to a certain size. Beyond that, it's a little tougher. There are electromechanical solutions but none of them are as simple and elegant as an air actuator with spring return.

 

[btrueblood]

Rotork uses both steppers and directly-driven 3 phase motors. They can give battery backup supplies as rmw says, and I'm pretty sure they can power either stepper driven or 3-phase motors.

We buy a lot of actuators for our products from a variety of manufacturers. I could give a list here, but anybody can get that same list with a little bit of effort using Google or GlobalSpec searching. Fail-safe, battery backup, spring return, fire actuator...are some of the variety of terms used for the devices.

Electric actuators can be made to fail (under power loss) in a variety of ways.

Some smaller actuators use a wound spring and clockwork mechanism.

Some use so-called "supercapacitors" and a switch mode power suppliy (boost converter) to provide the power to drive to a failed position. They operate instantaneously, there is no reset of the actuator controller. The boost converter is always running but provides a slightly reduced output voltage, or is blocked by diodes, so that no significant power is drawn from the capacitors until the line power falls below a threshold. Some of these are quite nicely packaged and very elegant, having a torque output vs. volume that compares very favorably to a pneumatic actuator.

Some use a dry-, gel-, or wet-cell battery and SMPS for power backup, operating much the same way as supercaps (most commercial PC UPS boxes use these). Typically, yes, a battery monitor circuit must be included and regular maintenance is advised (some backups can check battery health, and signal the controller when maintenance is required).

 

[rmw]

Electric actuators with spring returns have to have sufficient motor power to overcome the spring forces before they apply the first bit of force to drive the valve stem. That is why their sizes are limited to small sizes. Larger valves that require lots of thrust would require humongous actuators to overcome the spring and provide the required valve thrust.

But as Btrueblood states, they do exist.

Sorry, BTB - I mis-spelt Rotork's name. Did I get the actuator model right? It has been quite a few years since I dealt with them.

I really did like their little stepper motor models. They were well built and accurate. I also liked Beck a lot too. They had valve actuators, but their specialty was syncronous motors. Their specialty was also making great actuators.

rmw

 

[btrueblood]

rmw,

I'd bet you had it close enought for google to find it...at least, when I type in your spelling, google corrects it to mine (but maybe google remembers me).

Our sister company uses Jordan actuators, and if the model was current then, it should still be usable (so they tell me). That may change at any time, we know how marketing consultants can be.

Rotork has a bewildering array of actuators and gearboxes, so I find it best to call in their rep. and give them a list of requirements. For all the gee whiz of their company and products, most of our customers opt for cheaper brands.

FWIW, I don't dislike pneumatic actuators, especially on larger valves, but they can be a PITA - you need a reliable source of clean, dry air for one. Controllers (positioners) for control valves (not on/off valves) can be spendy, and most of them spill a bit of air continously during operation. For a spring return pneumatic, managing the spring size vs. air line pressure and the shape of the torque curve is a problem - you need max. torque to shut off most valves, and that is where a spring-return actuator will generally be its weakest, so the result is a compromise/overdesign of both spring and piston. Also, the time for a pneumatic system to "fail" (i.e. time for the actuator supply pressure to fall below some level) can be indeterminate, depending on how the system fails; generally electrical systems fail all the way or not at all, and do so quite quickly and reliably. Add into all of this that air compression is inherently lossy (due to motor/compressor inefficiency and due to inevitable leaks in the system) - so unless the pneumatics satisfy other concerns (explosion proof system as an example) or is already in place, electric motor drives are generally cheaper (both in first cost and operating costs), and at least as reliable as pnuematics.

And, for some valves in our plant, we rely on the one proven all-weather actuator: our lead shop technician, who lives only a few miles away and is on the first-to-call list...

 

[rmw]

BTB, I live by the adage that "clean dry instrument air" is an oxymoron. Jordan used to have a handout that showed how to calculate the total cost of compressed air and, yes, it is not cheap. I've cleaned plenty of oil out of positioners and other valve parts from "clean air."

rmw

 

[btrueblood]

rmw,

We are lucky in that our shop air compressor is brand new and "oil-less" (and thus not leaking copious amounts of oil...yet), the chiller/drier same (the drain valve has not yet plugged or failed), and all the piping is newly laid (we decided not to use the previous tenant's PVC air lines that were nearly half full in places of oil sludge and whoknowswhatelse). But I caught a new shop tech oiling a tool by dripping it into the end of a flexible hose rather than the tool itself, grr.

FWIW, I/we've had my/our share of trouble with electric actuators too.

 

[gerhardl]

Hi all, please let me join with some comments from Scandinavia (Europe).

All said above is 'true' from an European viewpoint, but in addition:

It is an existing trend giving a movement towards using electrical actuators, if necessary with UPS backup (battery) systems, for water mains in Europe (worldwide?). This solution is commonly used for drinking water mains (often at critical, but not the highest critical / highest risk applications and for intake valves for hydro-electrical plants (low pressure at highest point). The highet risk points might be provided with mechanical closure (weight and lever)/oil hydraulical for opening (bursting) closure mechanisms, instead of electrical.

Commonly you have to take into consideration following points to minimize your UPS backup system for electrical operation.

a) Lowest posssible torque. Indicating natural selection of low-torque valves, typically double eccentric high-quality BFL valves, with mounted high quality gear constructions, typically slider-cranck construction.

b) Longest possible closing time, keeping size of actuator down, using actuator gearing (in addition to valve gearbox) and additional time instead of actuator with higher output kW, but also to prevent water hammer.

c) Actuators are then to be selected standard high-quality actuators with standard 24VDC, 48VDC (not often 110VDC, mostly for older hydro-electrical plants) and 240V50hz (European standard, US would be 240/60) provided from UPS backup by electrical mains fall-out. (Actuator: any quality brand, Rotork often used for petroleum ralated processes, AUMA dominating for water mains in Scandinavia )

Lastly: I would not be happy providing a standard ballvalve (above a 'smaller size' say limited to 2-4" and in complete SS) with an electrical motor for 'water mains', because of possible increasing torque over time.

If electrical actuation is required because of regulation this valve would typically be selected as a regulating valvetype for full regulation (droptight closure types available) or if a closing valve (or limited regulation inline at lower pressure) a double eccentric BFL.

Only exception for electrical operation of larger ballvalves are double eccentric ballvalves, which regarding electrical operation, can be directly compared to double eccentric BFL valves for consistent torque.

See for instance

http://www.erhard.de/index.php?ERHARD_Ball_valve

(Please read me correct, there is nothing against larger non-eccentric ballvalves electrical operated where fluid (and construction) ensures a lower risk of uncontrolled increasing torque over time.)