Parker CPI Critique: Series III
on
Fitting Seat Finish
“The smoother the surface, the better the seal” says
And
we
a
competitor.
retouched photo sfwtfmr The seat of the iPLstainless steel instrumentation fitting on
totally agreeBEhtit’s why
burnish the seafllQlfc’Parker CPI stainless steel instrumentation fittings. Now whadoesn’t our competitor take his Own advice? we
the rigffh4sQ)urnished to achieve a smoothness of from 5 to 8 on aRMSscale. The competitive fitting on the left has an unburnished seat app may have a RMS as
Industry tests have shown that a 50% improvement in the surface
finish of a seat can result in an 800% improvement in the sealing of a fitting. Parker CPI (and to our knowledge only Parker CPI) burnishes the seats of its stainless steel fittings for two reasons: 1) To smooth out the microscopic-
and, 2) to
ally pitted surface, harden that surface substantially. Here’s what happens:
high
as
32.
Seat Finish Parker Roller Burnished Seat 5-8 RMS
Competition Standard Cut Seat 32 RMS Max.
Burnishing defined* Smoothing surfaces
through
frictional contact between the work and some hard pieces of material such as hardened steel rollers. Definitions of metallurgical terms by the ASM Committee of metallurgical terms. American Society of Metals/ September 1977
Flattening the Peaks and Valleys The smoothness of a surface is defined by its RMS (root mean square) value. The lower the number, the smoother the surface. Glass surfaces usually have a smoothness of from 2 to 5 RMS. Parker CPI burnished stainless steel seats range from 5 to 8 RMS. Unburnished stainless steel seats in competitive fittings have gone as high as 32 RMS. When you have a stainless steel fitting that does not have a burnished seat you have potential sealing problems. The unburnished seat has microscopic peaks and valleys that can cause leaks. In remaking a stainless steel fitting with an unburnished seat, you are still attempting to uneven seal against the same surface and still have the potential for leaks.
Hardness also makes a better sealing surface. When Parker CPI burnishes the seat of a stainless steel instrumentation fitting, it is hardened beyond the hardness of the ferrule it seals against. The Rockwell Hardness Measurement Scale shows that burnished seats are 20% harder than the stainless steel ferrule. This makes the seat practically impervious to the scuffs and scars that can occur when a fitting is remade often. You get a tight seal every time.
Parker CIRCLE 169 ON READER SERVICE CARD
Burnishing is value-added. There is of course, extra time and expense required in burnishing seats. But the resultant quality finish and reliability are well worth the operation. That’s why Parker CPI burnishes the seats of its stainless steel and monel
fittings. If you would like more information on this and other steps that are taken to ensure top quality CPI fittings, we suggest you contact, our Chief Engineer, Fred Zikas, at the Parker Hannifin Corporation, Instrumentation Connectors Division, 9400 South Memorial Parkway, Huntsville, Alabama, 35802.
