Motor_operated contor valve??? Is it proper??

[TAGE]

Dear All
I'd like to know that if i can use motor actuator for the control valves (regularing purpose, not on-off purpose). Normally we use the pneumatic actuator for this kind of control; such as desuperheater, feed water system and so on. Even though I know the motor actuator of which technologies have highly been developed but I'm not quite sure that whether it's proper for regulating purposes or not. I do hope that there would be someone making me for clarity of this my concern and please share me your experiences.

Thanks indeed and best regards

 

[jsummerfield]

No. You can do anything that you want. However electrical motor operated actuators are not well suited for control.

An electrical motor operated valve normally operates a gear operated gate valve at 12-inches travel per minute. Too slow for most control applications.

An electrical motor operated valve does not typically operate for prolonged periods.

Lacking stored energy, an electrical motor operated valve lacks a fail position.

If you have a reason not to use a pneumatic actuator such as a small remote site, consider an electro-hydraulic actuator.

John

 

[TAGE]

Thanks John for you suggestion
Thanks so much for all suggestions
In fact, I thought like what you suggested, what I'm concerned is we cannot do fail safe operations if power has gone as well as the lifetime of the motor actuator over the frequently-regulating operation. I really have no idea why the main contractor who is being awarded the project really wants to supply this type of actuator since, in my view, the cost of motor actuator is probably higher than the pneumatic actuator!!?? (I might be wrong) i'm not sure that if we consider overall an instrumentation-compressed air system (Higher capacity of compressors, piping and pneumatic actuators), we might need more investment for pneumatic system than power lines and motor actuators, don't we?

Regards

 

[valvemover]

Tage,

These days electric motor operated valves are being used for many applications, including those of regulating duties. Whilst Jsummerfield is correct about the normal speed of operation as being 12-inches travel per minute, this definition seems to have come from many specifications describing open/close duty actuators.

In actual fact electric actuators can be supplied with faster running motors giving a faster response time. Actuator motors have also been specially designed with low inertia reducing the amount of overrun and the consequence of serious overshoot. Control and instrumentation techniques with electric actuators are easier to design and by their very nature are cheaper than appropriate controls required for pneumatics.

Jsummerfield mentions that there an electrically operated actuator lacks stored energy. Some end users/contractors/consultants, when convinced of a reliable power supply may warrant the dismissal of this fail safe feature. Alternatively, electric actuators are available with DC power supplies where a back-up power supply can be given through a battery. I have also seen applications where UPSs have been used.

Sorry, my latop battery is losing its charge (no fail safe, but only because I couldn't be bothered to pull the power chord out of the bag.

Hope this little helps.

Kind regards

valvemover

 

[JimCasey]

Yes, electric actuators are acceptable for control.

Most rotary valve companies offer rotary electric actuators with positioner cards in them, and some, such as Worcester, offer digital positioner boards and integrated digital process controllers. Housings offered are general purpose, weatherproof, or explosionproof.

Several companies are offering electrohydraulic actuators, where the primary energy source is electric, driving a hydraulic pump pressurizing an accumulator. A cylinder drives the valve and the accumulator provides for fail action. (Rexa, Jordan, Worcester)

Electrics have a real advantage where it is impractical to supply air to power a pneumatic actuator. They can even be powered by solar power, and controlled by radio link if in a highly remote location such as an oil well.

They are almost always slower than air-actuated valves. Some systems do not need quick, frequent control. They are also stiffer than pneumatic actuators, so turbulence or pulsations in the process does not deflect the valve plug from its control point.

 

[ALEXFV]

TAGE:

There's a huge amount of control applications where motorized valves are used. It depends on quality of electric actuators, and Class of modulating service. As per valuable comments of everybody, you must review your application. You can have an easy approach at

http://www.bernard-actuators.com

about modulation Class.

Have your heard about intelligent actuators? This kind of equipment can provide finest modulating service as well as fail safe capabilities. There's also spring-return actuators even for high torques.

If you provide more information on your application, I will be happy to help you.

Good luck

 

[TAGE]

Thanks calfer for your kind help so far,
Yes I've heard about intelligent actuators but my concern is will the awarded contractor supply such expansive type?? If they do so, no doubt about it at all. Considering the worst case, unless they will supply the good one, just ordinary motor actuators, in order to reduce the project cost. what would happen? As you know i'm an owner engineer, i have to work with this type in the long term. Frankly i'm not familar with it. The contractor will use motor actuators for controlling "All" regulating control valves in the power plant!! for instance; feed water, desuperheater, make up water system and so on. These are my application.

PS i cannot visit your recommended web site, it may no longer be available but thanks so much anyway.

 

[jsummerfield]

Can you mention the typical actuator manufacturers and models?

John

 

[valvemover]

Tage, hello.

You are concerned about the contractor perhaps providing an actuator not meeting your requirements.

This is an issue which owner engineers/contractors and consultants are often confronted with.
Question: Does a specification for your project exist? If it does and that spec. describes certain features that the actuator must have e.g. intelligent controls, positioner, etc. then the contractor has to abide by that spec. Usually the consultant or owner engineer reviews the actuator data proposed by the contractor to make sure that it complies with the spec. before the proposal is approved.

If you are having problems reaching the Bernard website I suggest you try AUMA at

http://www.auma.com

They have a good and informative website on all applications. Their products are also modular meaning you can upgrade existing products to do something else at a later date, for example you can have the control system replaced by fieldbus.

Hope this helps, good luck

 

[hacksaw]

electrics are fine (though not a personal favorite) however they do require a significant increase in engineering to implement them properly.


as a rule, they are not very forgiving if the design requirements are not spelled out in complete detail...

 

[4carats]

What do I need to specify in engineering a motor operated valves?

 

[hacksaw]

an electrical engineer! actually there is a lot of detail, typically a half dozen pages of functional specifications just for the operator and its controls.

 

[jeffvalve]

Try

http://www.rotork.com

. They are probably the most well known electric / hydroelectric manufacturer. They will cover most requirements

 

[GB67]

Try also SAR range of AUMA actuators (multiturn) or the equivalent for quarter turn.

Information on

http://www.auma.com

 

[valvemover]

Hi 4Carats,

Depending on where you are from you may like to try out AUMA USA:

http://www.auma-usa.com

Take a look under "Download Information" and review "Actuator specifications". You can find specs. for different applications including hazardous areas. If you prefer to have the specification in accordance with the European ATEX directives for hazardous areas I am sure the folks at AUMA USA will put you in touch with their colleagues from the parent company in Germany.

Good luck

 

[rmw]

Below is a good site for electric actuators designed sepcifically for modulating duty. This company is a div. of Rotork mentioned above, but designs actuators specifically for high modulating applications.

Be careful when using an electric for control service, because not too many motor type actuators are built for the rigors of true modulation.

Beware also, modulation is defined differently by various vendors.

If yours is one that requires tight control, you should specify an actuator that meets the 3000-4000 starts per hour criteria. That is hoveing around a start signal per second. Not all actuators that are called modulating are capable of surviving that.

Be careful of the feedback mechanism gear train. The best is to have the feedback device tied directly to the output shaft, or as close as practically possible. The more stages of gearing, etc., that a feedback device has to go through between itself and the actual output means the introduction of lots of hysterisis to the feedback signal.

Electrics have been successfully used by the electric power industry for many years.

Electrics and pneumatics each have their own pariticular sets of advantages and dis-advantages. You have to pick what suits your application best.

Remember that "clean dry instrument air" is an oxymoron.

rmw

The link is

http://www.jordancontrols.com

 

[TAGE]

Thanks everyone a lot for your many valuable suggestions, recommendations or even web sites to help me get information. For further useful suggestions, they would still be welcome..

 

[JimCasey]

Things you need for a good electic control-valve actuator:

1. High duty-cycle rating. 70% to 100% (Continuous)duty, also expressed in starts per unit time.

2. Electromechanical brake. Prevents actuator from drifing due to valve dynamic forces when in steady state. Self-locking designs or actuators on small ball valves may not need additional brake, but it still helps stop the actuator at the desired control point.

3. Manual Override. Sometimes the power goes out.
3a. Failsafe. Not frequently offered on electric actuators that usually just stay in last position. Electric failsafe is usually an added-on UPS with a power-failure sensing relay to drive the valve to safe position. Rarely, a spring failsafe is available-usually on electrohydraulics like the Worcester 72 or REXA.

4. Position-sensing potentiometer reading the position of the output shaft, not some intermediate point in the geartrain.

5. Optional: Anticondensation heater
additional limit switches
Analog output of valve's position(requires additional potentiometer, plus circuitry)Specify the signal value 4-20 ma, 0-1000 ohm, 0-10V etc.
Visual indication

6. Voltage rating to match power source: 120vac, 24Vdc, etc.

7. Input Signal to match the control system: 4-20 madc, 0-10V, 0-1000 Ohm, etc.

8. Positioner board should have as a minimum, adjustment for zero, span, stroke speed, deadband.

9. Housing Electrical rating to match the environment: General Purpose, Nema 4 weatherproof, NEMA 4X Corrosion resistant, NEMA 7-9 Explosionproof, FM Class 1 div1 group C,D for hazardous ares (usually accompanies NEMA7), CSA, Cenelec, JIS, all depending on where the actuator will server.

10. Actuator MUST be attached to the valve stem with a zero-lash, clamped coupling. The best actuator in the world will not control well through a sloppy coupling.

 

[itdepends]

To add to JimCasey.

Make sure the unit does not have any radio controlled parts.

We had a radio controlled motorised valve installed on a reduction furnace and the commissioning engineer couldn't work out what the bug was in the system. Every time he called up the control room to get the valve stroked/position moved it went crazy.

His radio frequency was interfering with the valve and causiing it to move.

 

[RR05]

I suggest you step back and look at your loop dynamics before deciding on actuator design. Even is sped up, an electric actuator will be slow and can cause loop instability on a fast loop, like pressure or flow. If your process is stable and does not have large upsets, then electric will work. Common example is a temperature loop, a slow loop that can be tuned to not cause hunting on the actuator.
There are many fine electric actuators manufactured that will not provide suitable control if missapplied. Start with your process first.