3 questions “Funnel the Spec” to one product type.
Start at the top, follow the path down, end on the recommendation. Designed for distributors to send a customer ahead of a quote call.
Question 1
What is the compressor doing wrong?
Won't load · won't unload · pressure swings
Question 2a
Is the symptom on the capacity-control side or the load/unload side?
If Won't match output to demand · runs full-load all day
Recommend
Inlet Control Valve
Inlet valve stuck open is the leading suspect on a rotary-screw that can't unload. Confirm with the intake housing off — if the solenoid clicks but the valve doesn't move, the valve is the part. Quote the cross.
If Won't start unloaded · hard-starts · overload trips
Recommend
Unloader Valve
Failed unloader on the startup-vent function. The motor is starting against full stored system pressure because the head isn't being vented. Quote the cross — same-day fix.
Running hot · running cold · water in the oil
Question 2b
Is the cooler side already verified clear (fan, fins, water-cooled supply)?
If Yes · cooler is healthy · still out of band
Recommend
Thermostatic Valve
Running hot with cooler verified = stuck bypassed. Running cold in normal ambient = stuck full-flow to cooler. Capture the original setpoint and quote the matching aftermarket cross — setpoint mismatch shifts the whole operating band.
If No · cooler not verified yet
Recommend
Thermostatic Valve
Verify cooler airflow / water flow first — fan, fins, and supply lines are cheaper eliminations. Then return to the thermostatic cross. Customers who've already replaced the cooler fan and are still hot are the warmest leads.
Electric bill spiked · runs continuously · oil out the intake
Question 2c
Continuous full-load with no unload cycle, or oil dripping at the intake housing?
If Continuous full-load · won't drop to unload current
Recommend
Unloader Valve
Stuck-closed unloader is the leading suspect on a 50%+ bill jump. Clamp-meter the motor — if current never drops to unload state, the unloader (or its pilot signal) has failed. Bundle with the rest of the control-valve set.
If Oil dripping at the intake filter housing on shutdown
Recommend
Inlet Control Valve
Inlet-valve seal failure — pressurized oil-laden air blowing backward through the air-end on shutdown. Quote the cross plus a new intake filter element (the old one is oil-soaked and unusable).
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.
SPC distributor playbook Compressor Internal Valves · how to cross-reference in one call