When to Use Gravity Feed
| Factor |
Gravity Feed Performance |
| Moving parts |
None — simplest possible system |
| Flow consistency |
Variable — decreases as tank empties |
| Output vs. pump |
Lower overall daily throughput |
| Height required |
8+ feet for acceptable consistency |
| Best application |
Low-volume, off-grid, or temporary setups |
Flow Rate vs. Tank Height
Every 1 foot of oil height above the inlet provides approximately 0.38 PSI of feed pressure:
| Configuration |
Pressure at Inlet |
Flow Variation |
| Full 55-gal drum, vertical |
~1.08 PSI |
Baseline, then drops ~83% — unacceptable |
| Last 10 gal in vertical drum |
~0.18 PSI |
~83% drop from full — unacceptable |
| Horizontal drum, 5 ft elevation |
~2.28 PSI |
~26% variation |
| Horizontal drum, 8 ft elevation |
~3.42 PSI |
~18% variation — acceptable |
Hose Sizing for Gravity Feed
Viscous oil creates a near-stagnant boundary layer inside hoses. Use the largest practical hose diameter:
| Hose Specification |
Recommendation |
| Absolute minimum (short runs, warm oil) |
5/8 inch ID |
| Recommended minimum |
3/4 inch ID (fits 1/2" NPT fittings on heater kit) |
| Preferred for gravity feed |
1 inch ID or larger |
| Oil temperature |
Heat to 120–160°F to reduce viscosity |
View PDF Manual ↗
