The challenge with heavy oil, grease and sludge is not only adhesion. At low temperature they are viscous and slow to move. Hot water changes their physical behavior before the water jet acts, so a normal pressure range can often give a more stable result.
Hot water is not merely hotter water
As temperature rises, oil and grease become less viscous and the contamination layer can flow and break apart more readily. On aged sludge, heat can also improve penetration through the outer layer, reducing the need for excessive impact force.
Cold-water high pressure versus practical hot-water pressure
Very high cold-water pressure can create splash and cut through oil without removing it from the work zone. A hot-water process softens first and then uses flow to carry soil away, which is often better for engines, gearboxes, rolling-mill equipment and construction equipment.
- Cold water: mud, dust and loose particles
- Hot water: grease, heavy oil, emulsions and oil sludge
- Steam: local carbon or narrow-gap residue
- Drainage: match wastewater volume and oil-water separation requirements
Temperature also has limits
Seals, coatings, plastic parts and electrical components all have temperature limits. Select a controllable outlet temperature around material, soil thickness, duty cycle and drainage conditions rather than pursuing the highest possible number.
How to Decide
For heavy oil, lower viscosity with heat first, then use practical pressure and sufficient flow to release and carry away the soil. This is usually more effective and controllable than simply raising cold-water pressure.