Valve Thrust/Torque Calculation 2

[jge1234]

Hi guys,

i am new to the valves industry.The thing is when we design a valve, the Thrust/ torque part of it is very uncertain, the actuator companies deal with it. I would like to know the physics part of it, namely the forces involved especially seat forces,friction, does the bonnet pressure come into play?
Any ideas?
Regards,
J

 

[bljnv]

Please follow

http://www.f-e-t.com/images/uploads/Torque Calculation.pdf

Also search for previous discussions on Vslve Torque
Regards

 

[Dean8573]

J

You get valve torques and you get actuator torques. they often come in the form of a maximum torque that can be applied to the stem before damage will occur and also operating torques. so ball valve will often have a MAST (max allowabe stem torque) and also BTO (Break to Open) torque required to intiate opening, RTO (Run to Open) the torque required to complete the majotity of the 90° operation and the ETO (End to Open) Torque required to fully open. You will find that the torque at the start will almost always be the highest followed by the ETO with the RTO being lower than both. Reason for this is the icreased friction when the ball comes in contact with the seat.

you will also ge BTC, RTC and ETC values, same principle as above but C = Close.

now when you fit an operator youu must exert force greater than the opertaing torques but lowe than the MAST figure, Actuator brochures will provide full torque details which can vary dependednt on pressure applied. For Oil and gas you build in factors of safety into the design to ensure that when required it will have more than enough force to operate the valve. this is open to each person on how they attack this but this is how see best.

Factor safety of 2 shall be used for BDV , SDV and ESDV valves with a factor of safety of 1.5 for standard valves. The maximum actuator output torque will be derived from the pressure calculated at plus at 10% ( please be advised that values stated in act brochures are minimum values exerted at that pressure so will often be higher. The valve MAST figure then divided by the ACT torque, if it is greater than 1 then the stem will not shear and can be deemed suitable. (please be adivised that if calculating the MAST figure as i do i will use minum material yileds etc and not actual yield as to ensure that it is suitable at minimum material standards.)

next i will take the valve torques and multiply them by the FOS and check against the actuator figures and ensure that the ACT has higher torque than the valve x FOS value. if both are achieved then we are good to go. Please also note that the valve operating torques should be used when subject to 100% delta pressure to simulate worst case.

Now....
Seat insert material plays a huge part with regard to friction, so Metal seat has very high torques in comparrison to PTFE, it is like a sliding scale, the harder the insert the higher the torques.

With regards to the bonnet it can be suscepatable to issues but these are more drivetrain dependent and can often be overcome with increaase bolt torques or inclusion of dowels. The main issues are mainly regading the valve stem but again these can be resoleved quite easily by upgrading stem material to a more durable and stronger material.

The type of valve also plays it part, some manufacturers have valves more suitable than others for this and not every valve will be ok to actuate.

hope this helps