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Valve Positioners

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Valve Positioners

Valve Positioners

Beta101

(Electrical)

(OP)

20 Jun 13 01:01

Hi,

Would appreciate anyone on the forum if they could shed some input on valve positioners and Actuators.

Are valve positioners required for On/Off valves (not modulating)? Are limit switches still required?

What’s the difference between electric actuator and motor actuator? Are they the same thing when discussed?

What type of actuators requires the use of solenoids?

Thanks

RE: Valve Positioners

Marco1975Inspector

(Petroleum)

20 Jun 13 05:48

Positioners are generally used on ctrl valves in order to have an accurate control of the valve movement.

You can install a positioner on an on/off valve , this will allow you to have an additional control over the device.
New generation of positioner are providing digital protocol data transmission on a dedicated bus ( Smart-Hart-Profibus-Fieldbus...etc)
allowing you to have additional information from the valve ( alarms , torque measurement to prevent jamming , etc...)

Also to provide the valve with limit switches is up to you ( or must be clearly stated in the specifcation you're are working with)

Electric actuator and motor actuator is the same thing.

What type of actuators requires the use of solenoids? Pneumatic type , to control the air flow that goes into the actuator cylinder

Regards
Marco

RE: Valve Positioners

gerhardl

(Mechanical)

20 Jun 13 10:56

In addition to above good answer:

Electric actuators can simply be on/off actuators normally with (for high quality) integrated limit and torque switches. For some el. actuators limit switches for intermediate positions can be added. Purpose: throtteling or first 70% fast closing rest slower (start stop to avoid waterhammer).

High quality el. actuators have integrated as standard, or possibillity for added electronic equipment, enabling all kind of signals and operations to make a valve 'acting' as a valve with positioner (even if not needed).

All fluid operated actuators need solenoid valves suitable for the fluid used, air, oil, gas, water etc.

In addition to above good answer:Electric actuators can simply be on/off actuators normally with (for high quality) integrated limit and torque switches. For some el. actuators limit switches for intermediate positions can be added. Purpose: throtteling or first 70% fast closing rest slower (start stop to avoid waterhammer).High quality el. actuators have integrated as standard, or possibillity for added electronic equipment, enabling all kind of signals and operations to make a valve 'acting' as a valve with positioner (even if not needed).All fluid operated actuators need solenoid valves suitable for the fluid used, air, oil, gas, water etc.

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RE: Valve Positioners

LittleInch

(Petroleum)

20 Jun 13 11:49

Are limit switches still required - only if you need to know remotely (control room) that a particular valve is open, closed or in transit (somewhere between open and closed). Actuated valves will have some form of this so that they know when to turn off the power and also many actuated valves can be opened and closed remotely so the controller and system need to know what is happening to the valve, but you also see it on critical manual valves if it is important. Sometime process engineers go a bit beserk on adding them to P & IDS which isn't really required. Critical valves sometimes have two limit switches if a trip would occur if the control system thought that the valve hadn't closed.

Motor actuators are normally the same as direct electric actuators, but you can get small self contained hydraulic actuators which work from an air or gas supply or occasionally electric power driving a hydraulic pump.

Solenoids are normally on pneumatic powered actuators, but can also be on hydraulic powered ones if you have a hydrualic supply system.

In addition to marcos good response I would only note in direct answer to your questions:Are limit switches still required - only if you need to know remotely (control room) that a particular valve is open, closed or in transit (somewhere between open and closed). Actuated valves will have some form of this so that they know when to turn off the power and also many actuated valves can be opened and closed remotely so the controller and system need to know what is happening to the valve, but you also see it on critical manual valves if it is important. Sometime process engineers go a bit beserk on adding them to P & IDS which isn't really required. Critical valves sometimes have two limit switches if a trip would occur if the control system thought that the valve hadn't closed.Motor actuators are normally the same as direct electric actuators, but you can get small self contained hydraulic actuators which work from an air or gas supply or occasionally electric power driving a hydraulic pump.Solenoids are normally on pneumatic powered actuators, but can also be on hydraulic powered ones if you have a hydrualic supply system.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Valve Positioners

Beta101

(Electrical)

(OP)

20 Jun 13 17:54

Thank you all for the prompt feedback and good answers. Would the solenoids in general be internal to the valve/actuator unit or is that something you purchase and mount separately? So would it be true to say that electrical actuators don't require solenoids? only pneumatic and hydraulic ones do?

RE: Valve Positioners

LittleInch

(Petroleum)

21 Jun 13 03:35

Electric aviators only need power cables and usually control cables to tell it to open or close.

Can be both. Often supplied loose or as a separate box by the actuator vendor so that you can mount them in a place whet you can get to them for installation and maintenence.Electric aviators only need power cables and usually control cables to tell it to open or close.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Valve Positioners

al1979

(Mechanical)

21 Jun 13 11:25

Just a thought.

Instead of asking here and getting bit by bit information from all experts, you can arrrange a 'Technical Presentation' from actuator manufacturers or may be a technical presentation on 'valve automation' from good industrial valve manufacturing company.

There are lot of actuator and valve manufacturers all over the world.

Cheers !!!!

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News

A valve positioner is a device mounted on the actuator that exerts or reduces air pressure as necessary to make sure the valve achieves the correct position.

When there is no positioner, the control signal goes directly to the actuator. When a positioner is installed, it intercepts this signal and then outputs a different signal to the actuator.

Positioners allow tighter control over the process variable by increasing the speed and accuracy of the actuator response. Because a positioner’s job is to make sure the valve is in the right place, it also helps in overcoming factors that affect control valve performance, such as friction, as well as problems like non-linearity and deadband. Positioners can also amplify or reverse an input signal as needed.

Essentially, a positioner ensures that the final control element in a loop exerts optimal control.

There are three types of positioners:

• Pneumatic positioners.

  These devices receives a pneumatic (air) signal from the controller and output a pneumatic signal to the actuator.

• Analog, or electro-pneumatic, positioners.

  Here, the input signal is electrical, rather than pneumatic.

• Digital, or smart, positioners.

  These positioners also receive an electrical signal, but it’s digital as opposed to analog.

Digital positioners came on the scene about 20 years ago, but they only really started gaining popularity recently as automation has started to take off in plants and along pipelines.

The main reason digital positioners are popular is that they can do much more than just control the position of the valve. The newest positioners on the market can also collect data about the valve to automatically alert users about how the valve and its assembly are performing, and even aid in diagnostics and maintenance.

Since they have fewer mechanical moving parts, digital positioners last longer than their traditional pneumatic and analog counterparts. Plus, they don’t bleed any air while the valve is at rest, which reduces energy consumption.

For example, the Masoneilan SVI II AP digital positioner allows you to:

• Auto tune the positioner in minutes, as opposed to the hours analog positioners can take

• Get diagnostic information about the health and performance of your control valves

• Identify potential problems before they happen

• Integrate the positioner with other control systems so all of your data is in one place

What this all boils down to is higher valve productivity, decreased downtime, and overall better plant performance.

Interested in learning more about the Masoneilan SVI II AP digital positioner? Contact us today.

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