304 stainless poppet valve cracking
304 stainless poppet valve cracking
(OP)
Stamped valve,304 stainless, 1/8 inch thick, temperature cycles from 40° to 140° quickly. Valve in pump head assembly. valve cracks at approximately 1000 hours, can anyone suggest a higher quality stainless that will still handle my chemicals and is less resistant to cracking.





RE: 304 stainless poppet valve cracking
RE: 304 stainless poppet valve cracking
RE: 304 stainless poppet valve cracking
The only heat treatment a 304 material can get is a solution anneal, which tends to reduce the yield strength over a stamped (cold-worked) part. Hopefully, the mfgr. is NOT heat treating the valves. Leave them in the cold-worked (as-stamped) condition for better fatigue strength. Maybe even shot-peen the surface...though you'd have to re-lap the seal face, so it might not help much.
140 F is no big deal for a CAT pump, we routinely operated these pumps, and similar ones, for thousands of hours at temperatures of 190 F/170 F cycling. Even a rapid chill from 140 F to 70 F (e.g. a temperature relief valve suddenly opening) would not affect the poppets much.
But, cavitation might - are you seeing a shiny valve become mottled in appearance on the downstream surface/outer edge? Is there something in the system that suddenly dumps the downstream pressure, allowing the pump to cavitate?
More likely, the valve is suffering from low NPSH at the hot condition (the pump may seem to "suck air" or have low output flow/pressure until the temperature drops again). Try improving the suction head (bigger and shorter suction line, tank elevated above pump), or (better) find a pump that has a larger bore diameter for the plungers - this has the effect of reducing the piston max. velocity and reducing the acceleration/deceleration that the fluid undergoes as it is pumped, with resulting better NPSH characteristics. If possible, consider a larger-capacity pump with reduced rpm, for the same reason (doesn't always help as much as #1 though).
Finally, a change in materials for the check valve may help, since you are using a high-pH solution - look at the precip.-hardening steels, 17-4 or 17-7 PH alloys, which can be heat treated to fairly high strength.
RE: 304 stainless poppet valve cracking
RE: 304 stainless poppet valve cracking
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Plymouth Tube
RE: 304 stainless poppet valve cracking
Contrary to the above, 304 can be heat treated, we do it to million of parts every year. We do a plasma nitriding process (commonly called ion nitriding) that gives us a case about 50 microns deep with a surface hardness of 750 HK / 100 gf. Treated parts are in a precision valve that does not leak or wear for over 1 billion cycles. Your mileage may vary.
RE: 304 stainless poppet valve cracking