Globe Valve Actuation Force 1

[KJ7]

Hi all,

My question is more fundamental than anything else, but it seems like I am really missing something here.

We are installing a globe valve as the one shown in the attached image in a 2” NPS piping line. The current piping design does not call for any supports assuming the piping will withstand the weight and the force of the valve. In attempts to figure out how much the piping will displace under the force exerted by the valve actuator as the valve operates we came out with a vector force of 10000 lbf generated by the actuator and transferred to the stem and the valve body. As you can imagine with 10000 lbf of force the piping around the valve deflects more than 0.25” and it fails code requirements.

We came out with 10000 lbf from the effective are of the pneumatic actuator and the air pressure requirements. The actuator is 17” in diameter and it is actuated with 50-80 psi of air. The valve is normally closed therefore the energy is stored in the springs in form of potential energy. Now… as the valve closes the potential energy, as I understand it, is used to overcome pressure and provide seating force needed to provide sealing. For the sake of argument lets assume the valve will be closing against 0 pressure, which will be the worst case scenario since there will be no damping of the closing.

I am to apply a point load at the center of the valve what do you think this value should be? The 10000 lbf of force it seems too high but I can NOT come out with a logical explanation of why it should be something else and what that value might be…
We are applying it as a static force considering the valve will be closing in 1-2 seconds.

Thank you for reading and have a good day!
KJ7

 

[CRG]

External applied force to valve should be 0 lbf. There is a gravity load; however, the actuator load on the valve stem is equal and opposite of that of the frame holding the actuator. Hence, the net force is 0 lbf.

Example: How much less will you weigh if you pull up on your boot straps with a 50 lbf force?

Perhaps I am missing something???

 

[KJ7]

Is it fundamentally correct to say that the only force transferred to the piping attached to the valve will be the impact from the valve stem into the valve body?

 

[chicopee]

The force to close the valve s/b equal to or greater than the force overcoming the spring resistance plus the force exerted on the disk at a position that it will nearly seat to shutoff flow plus some internal friction from linkage to stem. In my opinion,for a 2" valve, 10,000 lbf is extremely high. Spring resistance will be the spring constant times spring compression plus preloading on the spring when the valve is fully opened. Force on the disk, will be line pressure under no flow times projected area of disk.

 

[DavidCR]

I agree with CRG.

The force to apply on the pipeline due to the actuating actuator is zero. Only weight works. Which for a 2" valve may not be important.

It is all internal stress in the body, bonnet and actuator case.

For example: When the springs push down, the diaphragm case will tend to exploit above, the reaction of the stem on the seat will tend break bonnet bolts or mounting, etc.

You may draw a simplified model, to visualize it.

Imagine a cylinder with a piston inside, and air on one side of the piston and a spring on the other. The walls take the reaction of the forces.

 

[CRG]

KJZ you asked, "Is it fundamentally correct to say that the only force transferred to the piping attached to the valve will be the impact from the valve stem into the valve body?" No, as I stated above there is gravity. Pneumatic control valves operate slow enough to discount any transients from the valve plug hitting seat ring. If it were a long pipeline, there could be pressure transients; however, I do not believe that is what you are asking. I am beginning to think you are a student and not a engineering professional. If you draw a free body diagram of the valve, actuator, and piping, you might be able to answer your own question.

 

[KJ7]

Thank you all for the input.

Regards,
KJ

 

[DavidCR]

I reckon that even if we suppose that the stem or follower would be very massive and move very fast, because of the size, most of the resulting dynamic forces would be dissipated in the body and only a few percentage would be felt by the pipe.