Quincy Q005: Quincy QSI/QGV Series Error Code Q005

Symptoms

Discharge check valve is leaking back to the sump when the compressor is stopped. The sump pressure bleeds down overnight and the compressor short-cycles on startup.

Possible Causes

Check valve seat damaged by debris or corrosion from acidic condensate
Check valve spring broken or weakened, failing to close the poppet against back-pressure
Check valve poppet stuck in the open position by oil varnish or foreign object

Troubleshooting Steps

Step 1: With the compressor stopped and tank isolated, listen for airflow or hissing at the intake filter
Backflow through the check valve is audible as a rushing sound at the intake silencer
Step 2: Remove the check valve from the discharge line and inspect the poppet, seat, and spring
Replace the spring if free length is <90% of spec. Lap the seat if scoring is minor; replace the valve if seat damage is severe
Step 3: Inspect the valve bore for varnish or debris that could bind the poppet
Clean with solvent and verify the poppet drops freely by gravity when the valve is held vertically
Step 4: Check downstream for sources of debris - replace the discharge line filter if installed
Install a 40-mesh strainer upstream of the check valve if debris is a recurring problem

How to Reset

Reset: After check valve replacement, press Reset on the QSI controller. The alarm clears after a complete stop-start cycle confirms no backflow is detected.

Common Replacement Parts

2023-4040-00: Discharge check valve, QSI 200-300 (Spring-loaded poppet, 2-inch NPT, brass)
2023-4041-00: Check valve spring (Stainless steel, rated for 10,000 cycles)
2023-4042-00: Check valve seat lapping tool (Piloted arbor for 2-inch valves)

Frequently Asked Questions

Q: Why does my compressor start every hour overnight?
A leaking check valve allows tank pressure to bleed back into the sump and escape through the breather. The pressure drops until the start signal is triggered.
Q: Can I add a second check valve in parallel?
Not recommended. Instead, replace the faulty valve with a correctly rated unit. Parallel valves can create flow imbalance and water hammer during start-up.

Quincy QSI/QGV Series Error Code Q005