Seating load for Ball valve
Seating load for Ball valve
(OP)
Hi,
how much seating force required to control leakage for following requirements.
Allowable leakage when closed condition is 0.5cc/min.
The seating material used is Teflon
Operating pressure is 60psig
Differential pressure when closed condition is 70psid
Earlier i were trying with yeild stress value of Teflon for seating load(250psi)168lbf force,however one of articale from emerson defines 40lbf is enough to control 0.5cc/min at 50psig.More the force more the actuation torque required to actuate the ball.
would appreciate your valuable comments
Thanks
John
how much seating force required to control leakage for following requirements.
Allowable leakage when closed condition is 0.5cc/min.
The seating material used is Teflon
Operating pressure is 60psig
Differential pressure when closed condition is 70psid
Earlier i were trying with yeild stress value of Teflon for seating load(250psi)168lbf force,however one of articale from emerson defines 40lbf is enough to control 0.5cc/min at 50psig.More the force more the actuation torque required to actuate the ball.
would appreciate your valuable comments
Thanks
John





RE: Seating load for Ball valve
Now you know how much contact stress you need. Now figure out the contact area, which will allow you to calculate the required force.
The leakage rate you mention is a value selected to account for variations in the contact surfaces. It is not be part of your analysis on determining how much force you need to get a seal. Without in depth knowledge of the range of ball roundness, surface finish variability on the ball, and ball seat and dimensional tolerances, you will never be able to get a consistent leak rate of 0.5 cc/min for a given force. Way to many variables that are outside your control. You need to shoot for tight shut-off to ensure you are always under the allowable.
Ultimately, you will have to test the final result to validate your calculations.
RE: Seating load for Ball valve
Seat material, seat profile, seat preload, surface finish of the ball are >some< of the variables that affect this. USUALLY there is some preload built in to the assembly stackup so that the valve seals at zero differential when new. Virgin PTFE seats are bad to cold-flow so they may seal when new, but if you take the valve up to pressure and then relax the pressure, the valve may leak at low differntials.
RE: Seating load for Ball valve
Thanks for your valuable posts.
according to bcd,working on contact stress requirement using following empirical formula
fc=Sqrt of (P*E/2.88*As)
where
P= Radial load
E=Youngs modulus
As = Contact surface area
Once i finish will get back to you
Thanks once again
John