Flush the spray bar with a suitable cleaning agent at the end of each day’s work, or during any prolonged break, and drain it into a container for proper disposal. Never clean jets by spraying solvent through them: electrostatic discharge can ignite the vapour. Soak them instead. And because anionic and cationic emulsions coagulate on contact, a machine changing from one to the other must be drained completely and cleaned internally by a specialist contractor.
REA Technical Data Sheet No.3, Recommendations for the Cleaning and Maintenance of Spraying Machines for use with Bitumen Emulsion
Why spraying machines need a cleaning routine
Bitumen emulsion can be applied by hand, but for larger areas, and wherever uniform distribution matters, spraying is recommended. Small areas are sprayed through a hand held nozzle or a hand lance connected to a machine, with pressure applied either indirectly by compressed air or by pumping the emulsion itself. Larger areas call for purpose built high capacity machines.
Whatever the machine, residue is the enemy. Bitumen left in a bar or a jet hardens, blocks the flow and ruins the accuracy of the spread, and an inaccurate spread is the usual reason a treatment fails early.
Which solvents and cleaning agents
Where the datasheet refers to solvents it means non volatile, high flash point hydrocarbon solvents of the kerosene type. Proprietary bitumen cleaners based on terpenes or fatty acid methyl esters may also be used, but with care: some react with bitumen emulsion and affect both its application and its end properties.
- Use the minimum amount of solvent necessary.
- Carry out an appropriate risk assessment before using any solvent, using the supplier’s Material Safety Data Sheet and the conditions on the specific site.
- Internal cleaning of tanks, when it is needed, should only be done by a specialist tank cleaning contractor, who may use steam, hot oil, high pressure water, a cleaning agent, or a combination.
Bulk sprayers
The tank does not have to be emptied at the end of every day. Enough emulsion can be left to cover the heating coils, where they are fitted, and the tank topped up afterwards. It is good practice, though, to clean the tank out completely from time to time, so that bitumen residue does not build up and so that prolonged heating and pumping does not alter the properties of the emulsion.
The spray bar is different. It should be flushed through with a suitable cleaning agent at the end of each day’s operation, or whenever spraying is interrupted for any length of time, and drained into a suitable container for disposal in line with the regulations. Where no suitable container is available, the bar can be flushed back into the main tank: turn off the bitumen to the pump and open an air valve on the receiving side, which forces air through the bar and back to the tank.
Jets block if they are not flushed through. After flushing, the sprayer needs good circulation and a spray test before work starts again. Jets may be removed and soaked in a cleaning agent overnight, and must not be cleaned by spraying solvent through them, because of the vapour ignition hazard from electrostatic discharge. Drainings should not be returned to the tank. They are disposed of as non hazardous or hazardous waste, as appropriate.
Hand operated machines
- Rinse the end of the lance with solvent at every break in spraying, to prevent blockage, but do not clean it by spraying solvent.
- Empty the machine completely at the end of each day’s operation.
- Jets may be soaked in solvent overnight if required.
- Drainings go to waste, not back into the tank.
Changing between anionic and cationic emulsion
Anionic and cationic emulsions coagulate when mixed. Even a small amount of one in the other precipitates bitumen, which blocks the working parts of the machine and the spray jets.
The REA’s advice is to keep machines reserved for one type of emulsion. Where that is not possible, change over as infrequently as you can, drain the machine completely first, and have the tank and pipework cleaned internally by a specialist tank cleaning contractor.
Inspection and maintenance
Follow the manufacturer’s recommendations, and in addition make sure that:
- All hoses and seals are made from oil resistant materials and are checked regularly for leaks.
- Leaking glands are replaced immediately, since they reduce spraying efficiency and accuracy considerably.
- The plunger rod on small pump operated machines is kept lubricated with solvent. It tends to pick up a coating of bitumen, and the friction that follows breaks the emulsion and jams the machine.
- Where a hand lance is used, any flexible hose is rated for the pressures and temperatures involved and is securely attached at both ends.
Reference
BS 1707:2018, Road surface dressing, bond coats, seals, preservatives and other spray applications. Specification for the method of test for binder sprayers for accuracy of spread of binder, the spray bar bench test.
Related guidance
Cleaning sits alongside the handling rules. How bitumen emulsion should be stored and handled covers temperature limits, drums and bulk storage.
For what the machines are spraying, see what bitumen road emulsion is, or start at Discover REA.