Valve Stem Threads 1

[pingmi]

Hi,

It is observed that Valve Stem / Bonnet thread profiles are either ACME or Trapezoidal in most of the designs. I was wondering why other thread profiles like Metric, UN are not used for this application. Any reasons?

Thanks in advance.

 

[gerhardl]

....depending on where the valves or stems are produced, type of valve, and to what norm and market.

For European produced valves to EN standards you will find other standards commonly used also for stems.

 

[bcd]

Power screw threads are normally used because the purpose of the stem is to raise or lower the control element or obturator inside the valve. The surface angle and thread height of ACME type threads generates less contact stress and wear than UN. Also, with UN and other bolting type thread series, it will take many more turns to move the valve to open or close. Naturally there are exceptions and special thread series where it makes sense to use, but in general, ACME power threads are used on multi-turn linear valves.

From memory, ACME was the first power thread standard which many countries simply adopted after WWII.

 

[quaddie]

The Trapezoidal Power thread is the Metric version of the ACME thread: "The difference between Trapezoidal and Acme threads are relatively minor. Other than using metric metrology for dimensioning the thread geometry is different only in the included angle. An Acme thread has a 29.5° included angle (14.5° flank angle) and the Trapezoidal thread has a 30° included angle (15° flank angle)".