ball valve retaining nut torque

[simpledude]

Have a small ball valve (1" inch bore, 1.875" ball) and need to have a torque spec for sealing/seating the ball and seals with a retaining nut threaded in.

We aren't a valve company, designed one as an add on to another product line.

 

[JimCasey]

Torque is going to be a function of the valve design.
I looked at some Worcester instructions I have, but their design is based around controlled-compression gaskets and you take the retainer up to metal-to-metal. Your valve's internal architecture, profile and material of the seat, and a handful of other variables determine the torque, or whether you even need to measure it.

 

[simpledude]

I uploaded a detail view of the ball, seals and retaining nut to give more info. The seals are made of Ertalyte, we don't have a controlled-compression gasket as we were designing without one. The pressure rating is 5000psi.

Thanks for looking into it, hope the new info gives better idea what is required.

 

[MikeHalloran]

It looks like there's no entry chamfer for the o-ring around the nut's nose, so it may get torn during installation. Leave room for a backup ring or two in the o-ring groove, too. I assume the stem seal is just not shown.

While you're increasing the nut diameter and the body diameter to accommodate the entry chamfer, you can also provide a positive stop so the nut stops with the seats in the perfect position, and the threads just shy of bottoming.

As it stands now, the only depth stop you've got is the end of the nut and body threads. It's possible for that to work, if you whirl both threads so you have blunt ends on both, and full control over the exact position of the blunt ends.

The drilled hole at the bottom of the ball keyway allows line pressure to reach the stem cavity; was that intentional?





Mike Halloran
Pembroke Pines, FL, USA

 

[JimCasey]

The drilled hole at the bottom of the ball slot lets the pressure in the cavity ESCAPE, whent he valve is in the fully open position. Otherwise you trap liquid condensate, open the valve to heated flow, and the trapped liquid pressure in the cavity can rise until something involving liability happens.

With THAT design, figure out what preload your designers had in mind for the seats. Find the spec for the body threads. Figure out what angle of rotation of the thread corresponds to the preload. Then specify to insert the retainer until the seats contact the ball (in fully closed or fully open position) and rotate the retainer x number of degrees additionally. Example: 20 threads per inch is 50 thousandths per rotation. if they designed for 25 thousandths preload, then it's half a turn past contact.

I can't see what's going to lock the retainer in place, and Halloran's remarks about o-ring placement are quite prudent.

 

[hydtools]

What purpose does the o-ring serve? There is the vent hole in the ball and what appears to be a vent hole in the nut. That puts whatever is in the system on both sides of the o-ring.

Ted