Ice formation in a vapor recovery unit is a cold-season fault with warm-season roots: water enters the vapor path somewhere, collects in a low point, and freezes exactly where flow is narrowest. The result can be a blocked sensing line, a stuck drain, a sluggish vacuum or a unit that simply refuses to start on the first cold delivery of the week. Clearing ice safely and then finding the water source is the real fix, because thawing alone guarantees a repeat the next cold night.
Why Ice Appears in a Vapor System
Vapor recovery lines and units carry hydrocarbon vapor, but they also carry whatever travels with it, and water is a common companion. Water enters through worn shaft seals, damaged sump covers, open drain points and condensation when warm vapor meets cold metal. In normal weather the water drains or passes through as droplets. When temperatures drop below freezing, that water turns to ice at the worst places: narrow passages, sensing taps, valve seats and drain valves. A small amount of water that caused no trouble all summer can immobilize a unit in December.
The Places Ice Shows Up First
Experience points to a short list of favorite freezing spots, and checking them in order saves time on a cold morning.
| Location | Why ice gathers there | What it causes |
|---|---|---|
| Sensing lines and taps | Narrow bore, small water volume freezes solid | False readings, flutter, or controller alarms |
| Drain valves and pots | Collected condensate freezes in the valve body | Valve will not open, or weeps after thaw |
| Low points in vapor lines | Water pools where slope is weak | Blocked flow, hard vacuum, slow recovery |
| Vent and relief paths | Moist air passes through in cold snaps | Stuck elements, safety functions doubted |
Clearing Ice Without Causing Damage
- Stop using the unit and isolate it electrically before touching any part of it.
- Warm frozen parts gently with ambient air or warm water on the outside; never use open flame or boiling water on instruments.
- Open drains once thawed and let standing water out, noting how much came and from where.
- Run a short supervised test delivery and watch the readings that froze, not just the machine.
- Record what thawed where. The map of ice is a map of water, and water has a source.
Finding Where the Water Enters
After the immediate blockage clears, the important question is why water is in the system at all. Work the evidence: water at a drain pot far from the unit points to an upstream entry; water in one sensing line only points to a local seal; ice recurring at one low point in the line points to weak slope collecting everything that passes. Shafts and seals that weep in summer often reveal themselves in winter, because ice marks the exact spot where the drip ended. Fixing the entry costs less than clearing the same ice every week.
Keeping It From Coming Back
Prevention in cold seasons is mostly housekeeping done in autumn. Drain every pot and low point before the first hard frost. Verify that sump covers and seals are sound while the ground is still soft enough to reach them easily. Check that vapor line slopes have not been altered by later ground work. Where a particular spot freezes every year despite good sealing, insulation or heat tracing on that section, applied with the supplier’s agreement, ends the annual ritual. Units in severe climates sometimes justify relocation of sensitive components into less exposed positions.
When to Call for Service
Handle single frozen points on site, but call the service technician when ice returns in the same place after proper thawing, when a safety or relief path has been iced, or when thawing reveals damage such as a split sensing line or a weeping valve. Those symptoms mean water has a settled route into the system, and tracing it needs the drawings and the experience that service visits carry.
Can we just pour hot water over the frozen unit?
Warm water on external pipework is acceptable in many cases, but never pour it over instruments, controllers or electrical enclosures, and never use open flame. Gentle, slow warming protects both the equipment and the person doing it.
Why does ice form at one low point every winter?
Because that point collects water all year and freezes it once. The slope there may be too weak to carry liquid onward, or the water may be entering upstream of it. Trace the entry and improve the slope or the seal, and the winter ritual ends.
Does ice mean the unit itself is faulty?
Usually not. Most ice problems trace back to water entry points and layout, not to the machine. The unit is simply where the water finally froze. The machine deserves inspection only if repeated freezing has damaged components such as sensors or valves.
Luoyang Wohong Petrochemical Equipment Co., Ltd. manufactures vapor recovery units and supports cold-season operation with practical service guidance for station operators.