API6D Ball Valve dowels verification 1

[Angel25]

Hi everyone.

We are designing a ball valve in according to API6D 24th edition.
As regards the calculation notes relating to the drive train, in accordance with par. 5.20 of API6D, I would need to clarify how to check the dowels between the body/bonnet and bonnet/operator plate, in particular:
1) are the dowels considered part of the drive train? In this case they must be verified with the design torque (at least two times the breakaway torque) and with the allowables stresses indicated in par. 5.20.2?
2) the maximum allowable torque of the dowels should be higher or lower than the MAST of the stem?

Thanks for your help!

 

[SPDL310]

Angel,

I am not too familiar with API6D so take this response with a grain of salt, but in regards to your first question I believe it would depend upon the the intended purpose of your dowels in the design. Are they intended to prevent rotation of the bonnet under actuator forces? If the answer is yes then you should test them and ensure they comply with the allowable stress requirements of 6D. If you don't install the dowels at all is your bolting sufficient to hold the bonnet and actuator forces without deformation? If the answer to that question is anything but yes I would argue that it is an integral part of the drive train regardless of any other interpretation you may find.

In regards to the MAST of the dowel I believe that it should be greater than or equal to the stem torque. The stem torque should be limited by the keying or for stems without keys, a machined notch above the stem to bonnet seal to prevent a shear break at or below the penetration.

 

[Angel25]

SPDL,

Thank you for the answer!

I confirm that the dowels are used to prevent rotation of the bonnet/upper flange due to the action of the operator (gear or actuator). Following your reasoning, the dowels are part of the drive train, so they must be checked with the design torque as for the stem.

In our calculation we already take into account the torque resistance generated by the friction between the flanges due to the preload of the screws, so we check the dowels for the residual net torque. In this specific case the contribution of resistance to the torque of the screws is not sufficient by itself to resist the torque, therefore the dowels are necessary.

Considering that the dowels are an integral part of the drive train, I agree with you that their MAST should be equal to or greater than the stem MAST.

In the meantime, thanks for the clarification, if there are other considerations they are obviously welcome!

 

[Nick_Gray_88]

Having designed valves for API 6D monogram approval; the dowels are not of between body and bonnet considered as part of the drivetrain.
However, for sound Engineering you’d required the MAST of the dowel pins collectively to be many times that the valve Operating torque depending on the application.
From memory most end-user specs will required your stem to be 1.5-2 times max operating torque, with your thrust base, if used, as a multiple of that. Based on that the dowels would ideally be equal to the thrust bases rated torque??

 

[HitokiriAoshi]

^ nick is right.

you don't have to. but should if you want to be, 100%

but honestly, the point of the safety factor is to prevent the drivetrain from BREAKING due to excessive force. a broken dowel pin would just allow the top flange to slip a bit, potentially making the valve leak a bit. I honestly wouldn't bother. (or you can easily just put in 2 pins)

Luke | Valve Hax |

https://valvehax.com/