Three valves, all inside the rotary-screw package. The inlet valve runs capacity, the unloader runs load/unload, the thermostatic valve holds the oil in band. None of them are customer-installed — every line on this page ships through SPC as an aftermarket cross-reference keyed to the compressor make, model, and HP. This page walks the diagnostic, the cross, and the bundled service-kit attach for each one.
Tap any type to jump to its page. The Decision Guide further down asks three questions that funnel the spec to one of these.
Inlet, unloader, and thermostatic — the regulating loop that ships inside the rotary-screw the day the OEM built it. Not customer-installed.
The customer doesn't spec these — they fail them. Match the symptom to the failed valve, capture make / model / HP / serial, quote the cross.
"Won't load" can be inlet valve, unloader pilot, control solenoid, or discharge check. Isolate the part — symptoms overlap across all four.
Runaway bills from a unit that won't unload, a hot sump killing the air-end, water emulsifying the oil — the cost shows up everywhere.
A 160°F valve and a 180°F valve are different parts. Capture the stamped setpoint, or the replacement shifts the entire operating band.
Conrader anchors inlet and unloader, KELTEC the thermostatic — same-day US stock at 40–60% of OEM list versus multi-week OEM lead times.
Distributor-facing reading. The trade-off column is the one that closes the loop — every type buys something and gives something up. Knowing what each type costs you is how the right one gets on the quote without a callback.
Reading the brand bench column — the bar shows how many of SPC's tier slots (Industry Leader · Emerging · Economical · adjacent) carry an option at that product type. A narrow bench here is by design: compressor internal valves are specialist aftermarket cross-references, not a tier shop. Conrader anchors the capacity-control and unloader cross-reference catalog for North American compressor OEMs; KELTEC anchors thermostatic valves and separator service. Both ship same-day or next-day from US stock at 40–60% of OEM list pricing.
Draw a line from the customer's answer at the top to the type name at the bottom. This is the page distributors screenshot and send to a customer the day before a quote call — so the customer comes prepared with the answers, and the call is about the brand and the budget, not the basics.
None of the three valves on this page is a customer-installed item — they ship inside the compressor package the day the OEM built it, and they only come up again when the compressor stops behaving. Every quote on this page starts with the compressor nameplate (make, model, HP, serial) and ends with a bundled service event — separator, oil filter, intake filter, and oil on the same PM. The cross-reference math wins on price (40–60% of OEM list) and on logistics (same-day vs. multi-week lead). The diagnostic step in the middle is what separates the SPC quote from a generic parts retailer.
The customer doesn't buy these valves — they fail them. The conversation is diagnostic-first, nameplate-second, and a bundled service kit on the same lockout.
If the customer answers most of these at the first call, the second call is the quote. If they can't answer any, the compressor internal valves are rarely the only spec gap — flag it and push for a site walk.
The Control layer is what keeps a compressed air system running inside the band the rest of the plant was designed around — and what keeps it from ending up in the news when something goes wrong. Two jobs sit here: regulate the system so pressure, capacity, and oil temperature hold steady at the set point across changing load and ambient conditions, and protect the system so a single failure upstream cannot turn into a vessel rupture or reverse-rotation event downstream. The regulating side lives inside the compressor package — inlet, unloader, thermostatic and discharge-check valves running the load/unload, warm-up, and shutdown sequence on every cycle. The protective side lives on every pressurized vessel as code-mandatory ASME relief valves that respond to pressure alone, with no electrical signal and no operator action required. Get this layer wrong and the customer sees it everywhere — runaway electric bills from a compressor that won't unload, a hot oil sump destroying the air-end, a reverse-spin event at shutdown, an OSHA citation on an unprotected receiver. Get it right once and it disappears.
Three valves inside the rotary-screw package — capacity control (inlet), load/unload + startup (unloader), and oil-temperature regulation (thermostatic). Aftermarket cross-reference, keyed to the compressor nameplate.
The system-level safeguards — discharge check valves preventing reverse flow at the compressor and receiver, plus ASME-mandatory relief valves on every pressurized vessel. Code-driven spec, not a tier choice.
→Tell us the end-use, the rough flow, and what climate the unit would sit in. We'll come back with a configured quote — the right type, the right tier, and the upstream gear the warranty assumes.
—. We reply within one business day with pricing, lead-time, and configured parts.