Dual Seal End Pieces

Posted on October 15, 2015 by Mike

Motivation

For years, IMI-Flow Design has provided valves with end connections customized for the job at hand. When field disconnection is desired this means our carefully designed o-ring unions with their superior o-ring retention, but on system connections for an isolation valve a more permanent and tamper-proof system is required.

The dual seal end-piece design is a permanent connection which is far more reliable than other systems. While allowing IMI-Flow Design to customize valves readily, it provides redundant sealing mechanisms which make a leak nearly impossible.

What It Is

Beginning with the Unibody Accusetter (UA) and Unibody Ball Valve (UB) in 2002, IMI-Flow Design has offered a new style of end-piece. Since then, the design has proven highly reliable on more than a million units installed. It uses a metal to metal seal outboard of the connecting threads, which is almost completely immune to heat. An anaerobic thread locker keeps the end-piece from being loosened in order to ensure the pressure on this metal-to-metal seal. Inboard of the connecting threads, where the probability of heat damage is minimized, is an EPDM O-ring. EPDM was selected due to its excellent performance in aqueous environments and its excellent resistance to compression set.

Also visible in the figure is the retaining nut for the ball valve. By setting the compression on the ball valve seats separately from the torque on the end-piece, IMI-Flow Design is able to ensure that each is appropriate for its purpose: other designs can potentially require a compromise to seat tension or worse still inadequate torque on the body's sealing surfaces.

Bottom Line

IMI Flow Design can provide valves with the right ends to prevent the need for field-installed adapters. These ends will be installed at the factory and include exclusive and extremely reliable sealing systems. The net effect is less effort and fewer worries for the installer.

Why’s There A Nut Under That Handle?

Posted on by Mike

What?

Many products from IMI-Flow Design have an integrated ball valve for isolating the terminal. Under the handle of these ball valves there's a nut. This is called the "packing nut".

Concealed under the packing nut is... wait for it... packing. Specifically, there's a piece of PTFE which is squeezed by the nut to form a seal against the body and stem.

Here the packing is shown un-deformed, overlapping the bottom portion of the packing nut. In the actual valve it re-shapes itself and flows as the nut is tightened.

Why?

O-rings are great. As can be seen in the cross-section, we use one of them on our ball valve stem. Unfortunately all elastomers have an Achilles heel: it's always possible for some combination of temperature and chemistry to make them fail. PTFE is very resistant to heat and chemicals, but it isn't "rubbery". Thus the PTFE makes it possible to stop any stem leak, but the nut must be tightened to squeeze it against the surfaces. If the PTFE gets worn from turning the handle many times, the nut can simply be tightened a little more.

Also

It's important to note in the cross section above that the stem on IMI-Flow Design ball valves is "blowout proof". That is, there's no way that someone can loosen something and have the stem come out. This is an important safety feature which is widely accepted, but some of our competition has introduced valves lacking this feature.

The end connection design can also be seen. Again an o-ring is used to provide the primary seal. Again there is a secondary seal: in this case it is metal to metal. This end connection allows IMI-Flow Design to customize a valve so that both ends match their mating devices directly with no adapters. The dual seals on this end connection ensure that it will not leak.