Valve Diaphragm Failure — Sulfuric Acid Heap Leach Service
The valve body says "mining duty." The diaphragm says something else entirely — and it's the diaphragm that's in the fluid path.
The ALD70 diaphragm used in one mining valve line is rated for sulfuric acid only to 38°C (100°F), far below the temperature tolerance of the valve body materials. A valve specified from its body material and mining reputation can pair the right body with the wrong diaphragm, and the diaphragm is what the acid actually wets.
At a glance
| Equipment | ALD70 diaphragm used in one mining valve line |
|---|---|
| Fluid / service | Sulfuric acid, heap leach service |
| Material involved | ALD70 diaphragm compared with polypropylene, PVC or metal body materials |
| Failure mode | Diaphragm caps sulfuric acid at 38°C (100°F), far below what the body materials tolerate |
| Cause | Valve specified from its body material and mining reputation, pairing the right body with the wrong diaphragm |
| Corrective action | Hastelloy named by the vendor as direct substitute, an upgrade across the 75/90/100 Series MIN configuration |
| Verify before ordering | Confirm actual process temperature, not just ambient design temperature, against the diaphragm limit |
Two Materials, Two Different Ratings, One Valve
A control valve's pressure-containing body and its flexible diaphragm are made of different materials by design — the body needs mechanical strength and pressure rating, the diaphragm needs flexibility to actuate thousands of cycles without fatigue. That means they can, and often do, carry different chemical-resistance ceilings. Netafim's own ALD70 chart makes this explicit for sulfuric acid: rated to only 38°C, versus the much higher temperature tolerance of the 75/90/100 Series bodies themselves.
Heap Leach Solution Runs Warmer Than 38°C More Often Than Assumed
A closed-loop heap leach circuit recirculates leach solution continuously, often in hot climates, sometimes with real thermal input from the leaching reaction itself. 38°C (100°F) is not an extreme temperature for a leach solution — it's a routine one in warm-climate or summer operation. A valve spec that checks only "is this a mining-rated valve line" and skips the diaphragm's own chemical resistance chart can pass a submittal review and still fail in the field once actual process temperature is measured against the diaphragm rating, not the body rating.
Hastelloy Diaphragm Upgrade — Named by the Same Vendor
Netafim's own catalog names Hastelloy as the direct substitute material, available as an upgrade across the 75/90/100 Series "MIN" (mining) configuration — the same alloy the vendor names as the correct answer for chlorine gas, chlorine dioxide, and high-concentration hypochlorite, where the standard ALD70 diaphragm is rated "Not Good" outright. This isn't a third-party workaround; it's the manufacturer's own documented upgrade path for exactly this failure mode.
Frequently Asked Questions
Why would a mining valve rated for sulfuric acid fail in heap leach service?
Because the body material and the diaphragm elastomer can have completely different chemical ratings, and it's easy to specify from the body material alone. Netafim's own ALD70 diaphragm chemical resistance chart — used across its 75/90/100 Series mining valve lines — rates sulfuric acid to only 38°C (100°F), far more restrictive than the polypropylene, PVC, or metal body materials those same valve series use, which tolerate much higher temperatures.
What temperature is actually safe for a standard ALD70 diaphragm in sulfuric acid service?
38°C (100°F) maximum, per Netafim's own published chemical resistance chart for the ALD70 diaphragm material used across its mining valve lines. Heap leach solution temperature can exceed this in warm climates or during summer operation — confirm actual process temperature, not just ambient design temperature, against this specific limit before ordering the standard diaphragm.
What is the fix if a valve needs to handle sulfuric acid above 38°C?
Netafim's own catalog names Hastelloy as the direct substitute material — available as an upgrade across the 75/90/100 Series "MIN" (mining) configuration. This is the same alloy Netafim names as the correct substitute for chlorine gas, chlorine dioxide, and high-concentration hypochlorite, where the standard ALD70 diaphragm is rated "Not Good" outright.
Does this same failure mode apply to other chemicals besides sulfuric acid?
Yes — Netafim's own ALD70 chart rates nitric acid "Not Good" even at 10% concentration, and chlorine gas and chlorine dioxide both "Not Good" at any tested condition. Sulfuric acid's 38°C ceiling is the most likely one to get missed specifically because the body material and general mining-duty reputation of the valve line can make a spec reviewer assume the whole valve is rated for aggressive acid service at any reasonable operating temperature.
Specifying valves for a heap leach circuit?
Send James your actual leach solution temperature — not just ambient design temperature — and we'll confirm the diaphragm rating before you order the standard configuration.
Ready to buy or need a fast answer? Call, text, or email James directly — (559) 395-5500 · [email protected].
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Reviewed by James Riggins, 30+ years specifying water and chemical process equipment · Updated