A three-stage vapor recovery unit is designed to run unattended, but it is still a machine with pumps, a compressor, a cold chain, a membrane module, and an electronics panel. When it stops recovering vapor, it usually announces the fact through an alarm on the operator interface rather than failing silently. Learning what those alarms mean — and what to check first — keeps a station’s vapor recovery running instead of waiting through long callouts. This article is a practical guide to the most common alarms on a WHSH-series three-stage vapor recovery unit and the checks that resolve them.
Start With a Safe Diagnosis Routine
Before touching anything, follow the same safe routine every time. The unit operates in an area where flammable gas can be present, so confirm the atmosphere is within safe limits with a combustible-gas detection instrument before opening any housing or access point. Then switch off the main power — never work on live equipment. With power off and the area verified, you can inspect safely and let the unit’s own diagnostics point you at the cause. Most repairs on these units are quick once the correct subsystem is identified, and the alarm history screen is the fastest way to find it.
Phase-Sequence Alarm: The Unit Refuses to Start
The most common reason a freshly installed unit will not start is a phase-sequence alarm. The unit requires three-phase AC power with the phases in the correct order, and a phase-protection device watches for this and for low or unstable supply voltage. If the phase-protection indicator shows red at power-up, the phases are wrong, the voltage is low, or a connection is loose.
The remedy is straightforward: switch off the power, and with the supply isolated, swap any two of the three phase connections, then power up again and confirm the indicator turns green and the unit completes its startup delay. If the alarm returns, check the incoming voltage and the tightness and oxidation state of the terminals at the panel before suspecting the unit itself.
Vacuum-Pump Overcurrent: The Heat and Oil Question
The vacuum pump provides the negative pressure that drives vapor through the membrane, and it is one of the few components with a scheduled oil service. An overcurrent alarm on the vacuum pump usually points at one of three things: the pump is overheating, it is mechanically binding, or its maintenance interval has been reached.
Start by checking the oil level through the sight glass and topping up with the specified vacuum-pump oil if it is low, then feel the pump housing for excessive heat. If the pump is hot and the oil is old or emulsified, change the oil. If the pump is mechanically stiff even when cool, the wear is likely internal. With the alarm cleared by resetting via the administrator menu, let the unit run and watch whether the alarm returns — if it does, the pump should be serviced by the supplier rather than forced along.
High System Pressure: A Blocked Path or a Failed Valve
Normal operation keeps the system pressure in a stable working band. When the system-pressure alarm sounds, the gas path is being restricted somewhere or a control component is not doing its job. The usual suspects are a solenoid valve that is not opening correctly, a restriction or blockage in the piping, or a fault in the pressure-control system itself.
Check the pipe route from the tank breather through the compressor to the membrane: look for a closed or stuck shut-off valve, debris in the line, or a solenoid that is not cycling. Because a high-pressure condition can stress the membrane, resolve it promptly rather than repeatedly resetting the alarm. If the piping and valves are clear and the alarm persists, contact the equipment supplier, as the pressure-control logic may need adjustment.
Abnormal Exhaust: The Membrane and Its Feed
The exhaust concentration is the unit’s headline performance number, and an abnormal-exhaust alarm means the outlet is not staying within limits. The cause is almost always upstream of the exhaust: a solenoid valve that is not switching, a pipeline issue, or a membrane pressure control problem. It can also mean the membrane feed is not clean, with liquid or debris reaching the module and degrading its performance.
First confirm the gas-liquid separator and filters ahead of the membrane are clean and functioning, because liquid carryover is the fastest way to shorten membrane life. Then check the solenoid valves and pipeline for correct operation. If a clean, correctly valued system still produces high exhaust, the membrane itself may have reached the end of its service life and should be scheduled for replacement.
Logging, Alarm History, and When to Call for Help
The unit’s operator interface keeps an alarm history and logs the run, so you can see how often an alarm has recurred and whether it is tied to a particular condition such as an unloading event or a time of day. Use these records before calling the supplier — recurring alarms with a pattern are much easier to diagnose than a one-off event, and the logged timestamps tell you exactly when and how often the trouble appeared.
Some failures are beyond a station’s field team and should be handled by the supplier’s service support rather than forced. If a fault cannot be resolved on site with the checks above, stop the unit, keep the area safe, and contact the equipment supplier for remote or on-site support. Following this sequence — safe atmosphere, power off, check the obvious subsystem, review the alarm history, and escalate when needed — keeps a three-stage vapor recovery unit reliable and prevents small warnings from becoming long downtime.