Plug valves solve downtime problems where ball valves failed at paper mill



A paper mill plant maintenance manager contacted Flotech about problems with stainless steel ball valves on the white liquor clarify tanks. (The solution of caustic and sodium sulfide is referred to as “white liquor” in the pulp/paper industry. These chemicals along with the heat and pressure, release the lignin from the fibers in the wood.)

The ball valves were difficult to open and close.

In this process the media gets above and below the ball valve cavity and packs into place making the valves extremely difficult to operate. Additionally, when the ball valve is closed, the line pressure pushes the ball against the down stream seat allowing the media to get trapped between the closed ball and the upstream seat.

The customer tried ball valves with Teflon seats, metal seats and scrapper seats. None of these ball valves improved performance. When the plant goes down for outage the white liquor cools and hardens up almost like concrete. When this happens the only thing the mill can do is to try inline high pressure flushing of the valves. Removing every single ball valve, disassembling, replacing seats, seals and packing would be cost prohibitive.  Quite often the balls are scored and need to be replaced.

We contacted FluoroSeal, a manufacturer of plug valves,  and asked for their help designing a solution.  FluoroSeal delivered a Teflon sleeved valve cutaway to demonstrate how the plug valve could solve the problem. The mill purchased a couple of valves for trial, and the replacement double block & bleed plug valves have been working flawlessly since. In these applications the Mill has replaced the majority of ball valves in sizes three through ten inch.

Why the FluoroSeal plug valve worked.

These plug valves are 316SS body material/ plug with the Teflon sleeve and packing. The FluoroSeal plug valve is a cavity less design. The diaphragm seal on top of the plug valve prevents the media from getting to the upper stem and packing area. The full Teflon sleeve and plug are always in constant contact preventing media from getting between them and from getting underneath the plug. Thus media build up is not an issue with the plug valve.  Additionally,  the plug is fully adjustable without removing the valve from service.This has saved our customer a lot of down time, unnecessary service work, and procurement cost in constantly having to buy new ball valves.


1. Bidirectional in-line bubble-tight seal independent of line pressure
2. Multiple external bubble-tight seals independent of line pressure
3. Direct mechanical three-point adjustment independent of line pressure
4. Independent travel stops
5. Full encapsulation and retention of all leading edges of PTFE sleeve and top seal components
6. Full lip at port openings protects PTFE sleeve
7. Contoured waterway ensures minimum flow turbulence characteristic
8. No body cavities to entrap flow media
9. Positive flow direction indication
10. Drilled and tapped flange actuation-mounting pads independent of cover and top seal assembly. This feature is optional on lever-operated valves (1/2″ thru 4″) in HASTELLOY®, INCONEL®, Titanium, and Zirconium alloys.