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How to Calculate the KW Rating of Motorised Actuator Valve

03/14/2014 5:22 AM

We often use MOV in OIL & Gas application but for kw rating we naturally has to depend on vendor. Please help by providng the process of calculating the KW rating of motorise valve(MOV).

Thanks in advance

with best regard

saraswata

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#1

Re: How to calculate the KW rating of motorised actuator valve

03/14/2014 5:44 AM

Become a vendor.

I'm not exactly being facetious about this. There are many decisions to make about how tight sealing surfaces must be, and then coefficient-of-friction calculations for umpteen possible material combinations, times opening/closing velocity.

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#2

Re: How to calculate the KW rating of motorised actuator valve

03/14/2014 8:34 AM

I found watt or VA ratings on the spec sheets of both (Harold) Beck and Honeywell Modutrol actuators in about as long as it took to type some terms into Google. If you'd asked for a Rotork wiring diagram, I could understand your frustration, because that is so difficult to come by. I think spec/data sheets are easy access to actuator power specs.

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#3

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/14/2014 9:51 AM

Take the actuator apart. Dissolve the encapsulating material around the wire. Count the number of wire turns in the coil. Measure the diameter of the wire. Measure the length of the wire. Note the color of the insulation. Note the color of the wire underneath the insulation.

Next, note the core material, length and width.

Now, look at the spec sheet and don't worry about dumb things like calculation of a needless number!!!!

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#4

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/15/2014 1:49 AM

Do you want to know the power rating of a MOV that is in service or do want to know how to calculate/determine the required motor power for a valve that is to be motorised?

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#5

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/15/2014 2:17 PM

do want to know how to calculate/determine the required motor power for a valve that is to be motorised..please help

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#6
In reply to #5

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/15/2014 2:28 PM

So, if you have a manual valve and you want to install an actuator to open and close the valve, you would be better off just ordering the correct motor operated valve from a reputable valve supplier.

You will NOT save money over the long run.

If you insist on pursuing this folly, get a valve and a torque wrench and MEASURE THE TORQUE REQUIRED to move the valve through its range of motion.

We used to make our own MOV's but the largest valve we used was a 2" valve, not in oil field service. We ate all the valve failures ourselves because neither the valve nor the actuator were certified for our service conditions.

Valve + torque wrench = power required.

Forget calculating this value. It will never work.

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#7

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/15/2014 3:02 PM

A standar formular for this is: Fparallel = Fperpendicular × CoF.

ξ

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#8

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/20/2014 9:32 AM

Contact and ask the OEM valve manufacturer for the valve operation torque curve.

Plot the torque requirements along the curve and select the motor size based on the requirements.

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#9

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/28/2014 12:28 PM

There is more to it than just knowing the valve size and type. Depending upon how fast you want that MOV to operate from open to closed, how it is geared, the types of forces against the valve, etc... can make a tremendous difference in how big the motor is and how many KW it requires to move the actuator.

I have seen some high speed MOV's that had to go from open to close in less than 5 seconds that required a 50 HP motor. Others where you could get away with a 10 HP motor if it was a slower actuator. Gate, plug and ball valves have all different requirements as well.

This also has an impact upon your wire sizing, voltage and starter contactor relays. Also the amount of pressure against a valve will make a difference in how much current the MOV requires to get the valve going.

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#10

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/31/2014 10:23 PM

Determine the torque required to operate the valve.

Determine the speed at which you want to operate the valve.

Using a standard motor base speed, determine the gear ratio you will need in order to operate the valve at that speed.

Once you know the gear ratio, use the torque required divided by the gear ratio to determine the motor shaft torque required.

Knowing the motor shaft torque and base speed requirements, use standard torque / power formula to get motor kW rating.

Being that you mention kW, we can assume metric measurements, therefore;

Motor Shaft kW = Torque (in N-m) x RPM / 9550

Example: you need 2500 N-m of torque to operate the valve, it turns 90 degrees.

You need to operate the valve in 10 seconds. That is 40 seconds for 1 revolution, that is .667 minutes. You use a 4 pole 50Hz AC motor, so 1450 RPM. So the motor turns 967 revolutions in that time (.667 minute), you need a gear reduction of 967:1.

To get 2500 Nm from a gear reduction of 967:1, the input torque is going to be 2.59 N-m of motor shaft torque.

kW then = 2.59 * 1450 / 9500 = .4kW (rounded)

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#11
In reply to #10

Re: How to Calculate the KW Rating of Motorised Actuator Valve

03/31/2014 10:43 PM

Even though the OP seems to have been impacted by a warp in the gravity somewhere....... I reckon your worked example was brilliant and clearly took some thought and effort.

I haven't checked if I agree or if the math is spot on but it "sounded" right. Checking it smells too much like work to me, it's not my actuator that needs spinning, and OP needs to do a bit of work.

I hope OP appreciates it. He can peer review it himself.

GA!

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#12

Re: How to Calculate the KW Rating of Motorised Actuator Valve

01/23/2025 7:13 AM

Why a <...calculation...>, with all the paraphernalia and assumption that process would entail, when it can be simply looked up (invitation declined) in the vendor information for the valve in question, or answered over a simple telephone call (invitation declined) to that vendor?

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