dear all,

can any one guide me the difference between the control valve and motor operated valve.. i am an fresher,.. i want to know the diff in application oriented

thanks in advance

 

Hellooo,

As i know, the difference in application that:

control valve is for throttling the flow, meaning that u will control the valve over the whole range from 0 - 100%, u can open ur valve at 20%, 55%, any value.

MOV (Motor operated Valve): used in ON-OFF applications, you can only open it (100%) or close it (0%) no control.

 

Keep in mind that with a proper positioner, motorized valves can be used to throttle flow, as well.

Example valves include the Jamesbury Hi-Performance Butterfly Valve, and the Fisher Control Disk.

Example positioners?... There are many that accept a 4-20mA position signal. EIM is a manufacturer that comes to mind.

Valve sizing is important when using a motorized butterfly valve for throttling flow, but that complex topic has been addressed in a dedicated thread elsewhere on this forum.

Hope this helps!

 

Control Valve

The control valve is essentially a analog device. the output of the control valve is controlled (as far as i have seen) is by a analog positioner. A 4-20ma signal is usually used in the positioning the control valve. fieldbus technologies promise to replace this, but sadly i have not worked with any field bus device till now.

The main advantage of the control valve include

a. Faster response
b. continuous, accurate positioning and control

Motorized control valve

Motorised control valve / Motor operated valves are usually for full open and full close applications. However there are places where they are used for position control as well. The main difference is that a digital signal is usually used to control the motorised valve. It typically has two control signals, one for the direction of the rotation and the other for rotating the motor. Like the I/P practitioner in a control valve which receives the 4-20ma controller input, the motorized control valve has a positioner card which receives the digital signal from the controller, limit switch, torque switch input from the operating stem etc. Motorised control valve can be classified into three types. however it must be noted that the main application of motorised valves are for flow control and flow isolation.

a. Open/close valves - used to automate manual open close valves, examples include, pump discharge / suction valves, boiler feed water isolation valves, drum vent valves, product line valves etc.

b. Inching valves - used were some degree of control, example a gradual opening and closing i required, applications include, reflux lines, boiler startup vent, boiler IBD valves, boiler main steam valves etc.

c. Precision flow valves - this is a precision inching valve, in inching valve the motor operates in steps configured in the controller, 5%, 10% steps . in the flow control valves which use MOV's. in precision flow valves a continuous control is enables by the use of proper feedback from the field to the controller which is not usually found in other motorised valves. An example is steam injection valve / water injection valves used in GT for Nox control.

thus the main difference between the control and motorised valve can be summarized as

1. control valves are used for precision control. however motorised valves are not usually used for precision control

2. control valves have a faster response as compared to the motorised valves.

3. control valves usually have a analog control element, while the motorised control valve have a digital control element.

4. control valves can be used for any type of control, pressure control, flow control, temperature control etc ... motorised valves are usually (if not always) used for flow control.

5. control valve usually are used in closed loop control, while motorised valves are predominantly open loop (with the exception of precision flow control valves)

 

control valve is the same as modulating valve, you can control the opening of your valve (your desire opening. it uses Analog signal.

motorized valve has an on/off, forward/reverse or close/open position. it uses Digital signal for the control.

 

dear sir,

thanks for your reply. i got an idea regarding that.. i am working in a power plant. may i know your mail id so that i can keep touch with u. it will help me to build my career brighter,,

expecting ur reply,,

Thnks in advance
R.Arunachalam
arunachalam.ice [at] gmail.com

 

Hi

I think you are speaking about 2 different categories which may not have conflict with each other. Motor operated is kind of actuator for some control or on/off valves. while you are speaking about control valve itself as the other category.

Regards

 

Good morning,

I came across this post and wanted to drop in my $0.02.

In a lifetime of working with and designing control systems, I have dealt with countless valves of one sort or another.

A Control valve does what it says, it controls flow. Whether it is an all or none or adjustable, it will control flow rate. I have used thousands of each kind over the years, some manually operated and others controlled automatically or remotely.

Likewise, a motor operated valve is simply a valve that uses a motor to actuate the valve mechanism. Once again this can be a on/off arrangement or adjustable depending on the type of controller used and the configuration of the valve itself as some don't really lend themselves to anything other than on/off.

The controllers I use typically control banks of solid state relays as the motors often pull significantly more current than the controller contacts can handle or the motors may require 3 phase power.

In a power plant, I assume you will run into many types of valves and many configurations. In most applications, from brewing to petrochemical operations, valves will be named by function. A control valve is generally at the starting point of a process or sub-process and generally turns the flow on or off and may be motor operated or manual. Other valves will be downstream finely control flow, temperature, etc. Lots of these where exact temperature control is needed like in a brewing operation.

Hope that helps. I guess to wrap it up is that the two terms actually describe two different characteristics. What the valve does and how it is actuated.

 

Dr. Price,

Your last sentence is the most concise answer to the question. A control valve controls flow-rate. A control valve can be operated by an electric motor, or is can be operated by a pneumatic actuator, or it can be operated by a hydraulic actuator, or it can be operated by a servo (an electric servo (stepping) motor, or an electro-hydraulic servo-valve which is used to control the flow-rate of hydraulic oil to a hydraulic actuator on a control valve).

Thank you!