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Torque Measurement of Quarter Turn Pneumatic Actuator

11/13/2016 11:45 PM

we have tested pneumatic actuator torque using Torque Transducer (HONEYWELL MAKE), testing setup given below.pneumatic actuator having spring we have not supplied air to that, we just gave hand toque that transfers to coupling of rotary (sctoch yoke) box shaft through gear box.given torque opposed by the spring each 5 degree readings are taken directly. The characteristic curve was drawn by considering spring thrust torque alone (theoretical formal= (Spring thrust)*Scotch yoke length) / Cos Θ 2))

The curve characteristics of theoretical and actual both are same (U Shaped curve) maximum at 2 extremes. but we have found some offset an forward and theoretical curves.

Green - Forward curve (during compression of spring)

Red- Theoretical curve

blue- reverse curve(releasing spring)

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#1

Re: Torque Measurement of Quarter turn Pneumatic actuator

11/14/2016 5:17 AM

Is there a question?

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#2

Re: Torque Measurement of Quarter turn Pneumatic actuator

11/14/2016 5:35 AM

Why is there a difference between the forward and reverse curves?

Friction?

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#3

Re: Torque Measurement of Quarter turn Pneumatic actuator

11/14/2016 9:25 AM

Maybe you need a little grease eh...? You really need these measurements taken over a substantial period of time encapsulating the design life of the system....

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#4

Re: Torque Measurement of Quarter turn Pneumatic actuator

11/14/2016 10:21 AM

Maybe you should actually repeat cycle these torque tests through many cycles, and document ambient conditions of at least temperature. Maybe the grease gets stiff when cold?

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#6
In reply to #4

Re: Torque Measurement of Quarter turn Pneumatic actuator

11/14/2016 11:08 PM

actually we did 3 readings for forward and reverse stroke.

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#5

Re: Torque Measurement of Quarter Turn Pneumatic Actuator

11/14/2016 5:21 PM

I'm not sure I understand your physical setup, but what I see is that it takes more force when you are compressing the spring (friction plus spring force) than when you are releasing the spring (friction minus spring force).

In the first case, friction is adding to spring force, and in the second subtracting from spring force.

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#8
In reply to #5

Re: Torque Measurement of Quarter Turn Pneumatic Actuator

11/14/2016 11:22 PM

thanks

we are also think like what you said..

but friction always acts opposite direction to the motion? or

we consider it acts opposite (resist) to given force for forward stroke and acts same (helps) direction in reverse strokes?

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#12
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Re: Torque Measurement of Quarter Turn Pneumatic Actuator

11/22/2016 3:49 AM

When it approaches the closed position, the valve presents a higher torque requirement as the moving part overcomes the resilience in the seat material. All actuation has to overcome this requirement, otherwise the valve will not seal shut.

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#13
In reply to #8

Re: Torque Measurement of Quarter Turn Pneumatic Actuator

11/22/2016 4:24 AM

Yes, friction is not a curl-free field, if you're into vector algebra.

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#7

Re: Torque Measurement of Quarter Turn Pneumatic Actuator

11/14/2016 11:13 PM

why this offset in forward and reverse?

this offset because of friction?

(or)

given torque has to overcome spring thrust generating torque in forward and spring generating torque helps to reverse in reverse stroke?

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#9

Re: Torque Measurement of Quarter Turn Pneumatic Actuator

11/15/2016 7:56 AM

If you want to have both "real" curves you have to test with air in one direction and spring on the other. Both curves can be very different depending on the supply air pressure and the "bench set" and sprig rate.

Either of two curves may be well above the other. It is very rare that both curves be the same. Both are (for spring return actuators) in U form, but in both cases the maximum torque is at the beggining of corresponding stroke, that correpond with maximum toque capabilities.

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#10

Re: Torque Measurement of Quarter Turn Pneumatic Actuator

11/15/2016 11:12 AM

In the curves I see a self locking mechanism where in one direction you overcome friction and compress a spring. In the opposite direction, you overcome friction only. In the reverse direction, the spring does little more than pull backlash out of the system, but does not contribute much to drive the gear mechanism. I see this most often in worm gear drives with a 30 to 1 ratio or greater with the main differences in the selection of lubricant used.

I saw a case once where a user of house jacks got into trouble because he switched to a Teflon bead filled grease and his jacks would start to let themselves down because of the lower coefficient of friction. The screw jacks were designed for lithium grease and the coefficient of friction with the new grease dropped from .1 to .017 and the screws became NOT self-locking.

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#11

Re: Torque Measurement of Quarter Turn Pneumatic Actuator

11/15/2016 6:07 PM

The torque required by the valve is a function of:

  • What's in the line
  • Its pressure
  • Its temperature

and the size, make and construction features of the valve in question.

If the capability of the actuator exceeds the requirements of the valve, the valve will travel when actuated. If it doesn't, then it is either incorrectly sized or there is a fault that requires attention.

Correct selection of valve and actuation is best done by the local friendly Valve Distributor, who will supply product warranty along with the product. There is no need for the user to carry this out.

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