Sizing questions arrive as horsepower requests and leave as disappointed owners when the unit was chosen from a brochure table instead of the station’s actual rhythm. Unload frequency, not tank volume, drives most capacity decisions.
Start with the Truck Schedule
Count unloads per week by day part. A station receiving three trucks each morning needs to clear a concentrated load; a station with scattered deliveries spreads the same volume differently. Morning-concentrated profiles demand higher instantaneous capacity plus recovery between trucks.
Convert Unloads to Vapor Volume
Each unload displaces vapor equal to the delivered volume, at a rate set by the drop time. Rough vapor flow equals delivered volume divided by unload minutes, adjusted for temperature. This working number, not the tank capacity, sizes the processing path.
Margin Without Over-Sizing
Capacity margin covers colder vapor, seasonal blends and the day a second truck arrives early. Twenty to thirty percent is a sensible planning band. Beyond that, oversized units cycle lightly and spend their life in inefficient corners of their operating map.
Processing Path Considerations
Condensation stages handle bulk vapor; membrane stages polish the tail. When unload frequency concentrates vapor in short bursts, stage timing matters as much as total capacity. Ask the supplier to model the actual unload profile rather than quoting on peak numbers alone.
Validate After Installation
The first month of operation proves or corrects the sizing. Log vacuum trends, cycle counts and recovery volumes per unload, then compare with the model. Units sized on real schedules rarely need rework; units sized on tank capacity sometimes do.