DISTRIBUTOR-FIRST SUPPLY PARTNER · SINCE 1999 Live · Compressed Air System
SPC Company
Compressed Air / Control / Compressor Control Valves / Inlet Control Valve
Layer 05 · Control Emerging · Conrader
01What it is

Inlet Control Valve

An inlet control valve is the throttle on a rotary-screw compressor's intake — a butterfly or poppet valve mounted to the air-end intake throat, downstream of the intake filter and upstream of the rotors. A fixed-speed air-end runs at a single RPM, so the only way to match output to changing demand is to control how much air it's allowed to breathe in. When the control panel calls for air the valve sits fully open; when system pressure reaches cut-out the valve slams closed and the air-end spins against no resistance, drawing parasitic horsepower only. Selected by cross-referencing the OEM compressor make, model, and HP to an aftermarket part number — year-of-manufacture variants often require different valve bodies, so a serial-number-level cross-reference is the safest path.

Compare tiers ↓ How to sell this ↓ Request a quote →
Where it's used General Manufacturing
General Manufacturing application
02Why it's needed

Why this matters.

Tips and pointers on when the inlet control valve is the right call — and when the symptom belongs to a different part. Scroll the strip →

01 · Key point
It modulates without cycling the motor.

Throttles the air-end intake between full-open and full-closed so the motor stays at a single steady RPM — the difference between roughly 90 kW loaded and 25-35 kW unloaded on a 100 HP screw. Replaces the impossible alternative of starting the motor 30+ times an hour.

02 · Key point
It seals the intake at shutdown.

Closed disc blocks pressurized hot oil-laden air from the separator tank blowing back through the rotors on every stop. Oil weeping at the intake filter housing is the unmistakable signature of seal failure.

03 · Key point
It crosses 40-60% under OEM list.

Atlas Copco, IR, Sullair, Quincy, Kaeser, Gardner Denver sell their own valves at full list with multi-week lead. Leading-tier aftermarket crosses ship same-day from US stock at roughly half the price — textbook aftermarket capture.

04 · Pro tip
Cross on serial number, not just model.

Year-of-manufacture variants within the same model line use different valve bodies — the single most common cross-reference miss. Capture make, model, HP, and serial before quoting. With the intake housing off, watch the valve on a commanded unload to isolate body vs. solenoid before shipping the wrong part.

05 · Where not to use
Small reciprocating compressors.

Small recips manage starting with an unloader and a check valve — no inlet throttle in the design. → Re-spec to an unloader valve for any reciprocating machine without a rotary-screw air-end.

06 · Where not to use
"Won't unload" before isolating the unloader.

Stuck-closed unloader produces the same surface symptom as a stuck-open inlet. If the valve moves on a commanded unload but the machine still runs full-load, → Re-spec to an unloader-valve cross — replacing the inlet won't fix the wrong part.

07 · Where not to use
Compressors still under OEM warranty.

Aftermarket cross-reference voids most factory warranties on the air-end and control package. → Re-spec to the OEM-genuine valve until warranty expires, then convert to the cross at the first post-warranty service event.

03Key selection criteria

What we need to spec it right.

From the machine spec sheet → to the part number. Answer what you know — leave the rest blank — and send.

01 · Input
Pull all three off the nameplate sticker on the cabinet — make/model is the primary cross key, serial resolves year-of-manufacture variants (the single most common cross-reference miss).
Atlas Copco GA · Ingersoll Rand R-Series · Sullair LS · Kaeser SX / ASK / CSD · Quincy QGS · Gardner Denver VS · Champion
02 · Input
Read the motor nameplate rating — sets the valve body size on the cross.
5-25 HP (commercial) · 25-100 HP (mid plant) · 100-200 HP (large plant)
03 · Input
Inlet valves are rotary-screw only. Small reciprocating compressors manage starting with an unloader and check valve — re-spec if recip.
Rotary screw fixed-speed · Rotary screw VFD · Large reciprocating
04 · Input
Read off the failed valve's casting marks or pull from the parts manual. Resolves the cross faster than serial-number lookup when available.
Casting marks · OEM parts manual · Maintenance log
05 · Input
Inlet-valve symptoms overlap with unloader, control solenoid, and pressure switch — get the customer to describe behavior before quoting.
Won't load (no air built) · Won't unload (runs full-load 24/7) · Oil weeping at intake on shutdown · Pressure swings wider than normal band
06 · Input
Failed solenoid mimics inlet-valve failure. With the intake filter housing off, watch whether the valve moves during a commanded load cycle to isolate body vs. signal.
Solenoid-driven · Pressure-pilot mechanical · Unknown — diagnose on site
07 · Input
Number of valves for this configuration. Replacement on multiple compressors? Add a separate quote line per machine.
1 valve · 2-3 valves (kit stock) · 4+ valves (multi-unit MRO)

Need different sizes, colors, or quantities? Fill the form, add to quote, then fill again — each click is one quote line.

04Choose your solution tier  ·  core differentiator

Whatever your lever — spec, value, or price — SPC has the right brand.

Most distributors sell one brand per product type. SPC's 60-brand portfolio means every Product Type page surfaces three real options matched to how your customer is buying today. Pick the tier; the quote desk handles the cross-reference.

02 Emerging 1 brand
Conrader
Conrader inlet / capacity-control valves
View brand →
05How to sell this  ·  distributor talk track

The tier conversation closes the deal. The cross-reference catalog wins the next one.

If the customer's rotary-screw is hard to load, hard to unload, or oil is weeping from the intake on every shutdown — the inlet control valve is the first part to suspect and the easiest aftermarket cross to win.
The SPC difference · how distributors actually buy

The 30-second positioning

The conversation is diagnostic, not catalog. Inlet-valve symptoms overlap with the unloader, control solenoid, and pilot circuit. Capture the four nameplate fields before quoting — make, model, HP, serial number. Serial number resolves year-of-manufacture variants, which is the most common cross-reference miss. With the intake filter housing off, have the tech watch the valve during a commanded unload: if it moves when the solenoid clicks, the valve is healthy and the failure is elsewhere; if the solenoid energizes but the valve doesn't move, the valve is the part.

Tier: Industry Leader tier — full cross-reference catalogs, in-spec gaskets, US stock. OEM-genuine only for compressors under warranty. Avoid no-name imports; a seal failure six months in costs more in downtime than the savings.

Bundle the control-valve set. On an aging machine, the unloader and thermostatic are usually also at end-of-life. Single-event invoices land $1,500-$4,000 with the bundle vs. $400-$1,200 for the valve alone.

Customer cue → talk move

""Our screw won't unload — it runs full-load all day""
Inlet stuck open is the lead suspect, control solenoid stuck energized second. Watch the valve on a commanded unload. Moves = problem downstream (unloader, control logic). Doesn't move = quote the cross.
""Oil drips from the intake filter housing on every shutdown""
Seal failure during shutdown blowback. Quote the cross-reference valve plus a new intake filter element (the old one is oil-soaked); stage the discharge check valve too.
""Pressure swings more than usual between cut-in and cut-out""
Sluggish actuator or sticking solenoid. Time the valve's response — slow response (more than a second or two) confirms the actuator. Replace the valve assembly.
""The OEM quoted $1,800 with a three-week lead""
Textbook cross-reference win. Quote the aftermarket at 40-60% with same-day stock. Next year's control-valve service is a no-question reorder.
""We have a VFD rotary-screw — do we still need an inlet valve?""
Yes. The drive modulates output via air-end RPM; the inlet valve still handles shutdown sealing. Cross-reference is identical.
""Compressor running hot, oil level correct, cooler fans working""
Possible inlet stuck open (can't unload, dumping heat into oil). Quote the inlet cross plus the thermostatic valve as a paired diagnostic.
Request a quote → Back to tier compare ↑
06Where it's used

Industries served.

Each industry below uses this product across the listed areas. Open an industry to see how it fits the rest of its system.

General Manufacturing General Manufacturing →

Also applies to Fixed-speed industrial rotary-screws, 25-200 HP plant range · $400-$1,200 · Fixed-speed lubricated rotary-screws, 5-25 HP commercial range · VFD rotary-screw compressors · Aging installed-base machines past OEM warranty · 8-15+ years old · Compressors with confirmed seal failure (oil blowback) · Compressors with load/unload control issues · Multi-machine rotary-screw fleets on service-route agreements

09Install · 6 critical steps

The things that matter on the first install.

Step 01
Confirm the cross-reference and stage the kit before lockout
Pull the OEM part number from the parts manual or the existing valve's casting marks. Verify body dimensions, actuator port location, mounting bolt pattern, and gasket configuration against the cross-reference. Stage the valve, fresh intake gasket, new intake filter element, and any bundled control valves on-site before locking out the machine.
Step 02
Depressurize fully, lock out, and wait for safe handling temperature
Stop the compressor, vent the receiver and separator tank to 0 PSI, lock and tag the disconnect. Wait until the air-end and oil sump drop below 120°F. The valve sits directly on the air-end — opening it hot or pressurized risks burns and oil splash.
Step 03
Photograph all control connections before disconnecting
Mark and photograph the actuator pressure line, solenoid wiring, and any position-sensor wiring. Inlet-valve plumbing varies by OEM and a misrouted line after install causes the next-day callback. Cap line ends to keep debris out.
Step 04
Remove the old valve and inspect the air-end intake throat
Loosen mounting bolts in a star pattern and support the valve weight while breaking the gasket seal. With the valve clear, look down the rotor intake throat for varnish, oil pooling, or debris from a failed intake filter. Clean the gasket face thoroughly before installing the new valve.
Step 05
Install the new valve with a fresh gasket, torque to OEM spec
Never reuse the old gasket — the valve sees pressure cycling on every load/unload and a reused gasket leaks within weeks. Seat the valve square to the intake, run bolts hand-tight in a star pattern, then torque with a torque wrench. Verify the actuator port faces the correct direction for the customer's control plumbing.
Step 06
Bench-cycle, install fresh intake filter, restart and verify two cycles
Before reinstalling the intake housing, manually cycle the actuator and watch the disc move freely between full open and full closed. Install a fresh intake filter element (never reuse — the old one is contaminated). Restart and watch through two complete load/unload cycles: full open on load, full closed on unload, no oil weeping at the intake on shutdown. Document install date, part number, OEM cross, and bundled parts.

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