Leak rates for PEEK + PTFE rotary valves 400 psig N2
at ambient temperature 150 ppm
Traditional valve test at 15,000 actuations
Norgren AFP valve with surface treatment, non-purge. Tested to 50,000 actuations
Norgren AFP valve with surface treatment and embedded purge (5 sccm). Leak rate below 0.01 ppm when tested to 150,000 actuations
purge (CLP) have been developed. CLP valves isolate each process groove of the rotor, elim- inating crossport flow contamination as well as outboard leaks. Because this new design incorporates the purge mechanism inside the valve, there is no need for external add-ons or bulky purge cabinets. This patented internal purge design is also the only way to isolate sample from carrier gas.
46 ppm The graph in Figure 3 compares nitrogen (N2
0.285 ppm 1.85 ppm ,
0 ppm 0 ppm
, , , 5 ppm , , )
leak rates of a traditional rotary valve, a valve with proprietary surface treatments only, and a valve with both surface treatments and inte- grated purge features.
Figure 3 – N2 leak rates for various rotary valve designs.
prevent contamination. The basic idea is that purge gas flows continuously, maintain- ing pressure that prevents sample gases from escaping.
Some users equip valves with purge housings or put the entire valve in purge gas cabinets
to achieve this. Now, the patented AFP™ design (Norgren, Inc., Littleton, CO) uses grooves built directly into the rotor so there is no possible path for leaks to get around the purge. Outboard leak purge (OLP) prevents leaks into and out of the valve. For more sensi- tive requirements, valves with crossport leak
Besides reducing leaks to near zero, an added benefit of the internal purge design is the abil- ity to monitor valve condition by verifying gas quality at the purge outlet.
Diaphragm valves Valves that use a diaphragm instead of a rotor to inject a sample offer several advantages for
AMERICAN LABORATORY • 13 • SEPTEMBER 2014
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