Heated Hoses for Plural-Component Spray

A heated hose is a paired hose assembly used with plural-component spray equipment to deliver isocyanate (A side) and resin (B side) from the proportioner to the spray gun at a controlled temperature. The proportioner’s primary heaters raise the materials to spraying temperature, and the heated hose maintains that temperature along a run that can extend tens or even hundreds of feet. Without it, materials such as polyurea coatings and spray foam would cool, thicken and mix poorly at the gun.

Why temperature must be maintained

Viscosity of most polyurea and foam components falls sharply as temperature rises (see rheology and viscosity). At the gun, the two streams must have suitable viscosity for impingement mix spray guns to mix them thoroughly. Temperature also affects reaction speed. If material cools in the hose:

• Mixing becomes poor, giving soft or streaky film.
• Pressure imbalance develops between the A and B sides.
• Patterns narrow and tails appear.
• Off-ratio material can result, with cure and adhesion problems.

Construction

A typical heated hose section includes:

• Two fluid hoses, one for each component, rated for the system’s working pressure. The isocyanate hose is usually made with a moisture-resistant lining because isocyanate reacts with moisture that permeates ordinary hoses.
• Heating element. Either a resistance wire wrapped around or running along the hoses, or a heated fluid circulating in a jacket.
• Temperature sensor. A thermocouple or resistance temperature detector near the gun end, sometimes called a fluid temperature sensor.
• Insulation and outer cover. Foam insulation surrounded by an abrasion-resistant jacket.
• Air hose and communication cable, often bundled in the same jacket, for air-purge guns and remote controls.

Hose sections typically come in fixed lengths that are connected to make the total run, with a short, flexible whip hose at the gun end.

Heating methods

Low-voltage electrical heating

The most common method in portable rigs. A transformer supplies low voltage that passes through copper elements in the hose. The controller uses the sensor reading to regulate current.

Circulating fluid heating

A heated fluid, often a glycol mix, circulates through a jacket around the hoses. This method is used in some systems for long runs and very even heat.

Sizing and length

• Inside diameter. Larger diameters reduce pressure drop for high-output systems and viscous materials but take longer to heat and hold more material.
• Length. Longer runs increase pressure loss and heat demand. Manufacturers state maximum lengths for each proportioner and hose type.
• Pressure rating. Hoses must be rated above the proportioner’s maximum working pressure, including surges.

Match the hose to the proportioner, material and output. Undersized hoses are a common cause of pressure imbalance.

Setting temperatures

Material data sheets specify the required temperatures for the A and B sides at the gun. In practice:

1. Condition drums to the temperature range the data sheet calls for before spraying (see drum transfer pumps).
2. Set proportioner primary heaters to bring material to spraying temperature.
3. Set hose heat to maintain the target temperature at the gun, not to add significant heat.
4. Allow the system to reach equilibrium before spraying, then check pressures and spray pattern on a test panel.

Never exceed the maximum temperature on the material data sheet. Overheating can shorten pot life in the gun and degrade components.

Field handling

• Avoid kinks and crushing. Damaged hoses can overheat at kinks and fail under pressure.
• Do not coil hoses tightly while heated. Stacked coils can trap heat and overheat the hose.
• Protect from vehicles and sharp edges. Use protective sleeves or bridges where hoses cross traffic.
• Keep hoses off hot surfaces and away from direct sun in extreme heat if possible.
• Elevate connections off wet ground.

Maintenance

• Inspect hose covers daily for cuts, abrasion and bulges.
• Check fittings and the fluid temperature sensor regularly.
• Test electrical continuity and resistance as the manufacturer instructs.
• Keep isocyanate hoses full of material or a suitable flushing fluid, never empty and exposed to air.
• Record hose replacements and faults in equipment logs.

See spray equipment maintenance for general practices.

Common faults

Safety

• Heated hoses carry materials at high pressure. A hose rupture can inject fluid into skin. Release pressure before disconnecting.
• Hoses are electrically powered; keep connections dry and follow the manufacturer’s grounding instructions.
• Isocyanate exposure can occur at leaking fittings. Follow isocyanate safety procedures.

Key terms

• Hose heat. The heating element inside or along the hose that holds material at spray temperature.
• Whip hose. The short, flexible final hose section connecting to the gun.
• Fluid temperature sensor (FTS). A sensor near the gun end that reports hose temperature to the proportioner.
• Transformer-based heating. A system in which a low-voltage current heats the hose conductors directly.
• Heat soak. Time allowed for the full hose length to reach set temperature before spraying.

Frequently asked questions

Can I use an unheated hose for polyurea?

For most pure polyureas, no. Some low-pressure or slower systems specify unheated hoses. Follow the material and equipment manufacturer.

How long can a heated hose be?

The equipment manufacturer sets the limit for each model. Longer hoses demand more heat and pressure.

Why is the isocyanate hose special?

Isocyanate reacts with moisture. Standard hoses allow moisture to permeate and form crystals inside, so moisture-resistant linings are used.

Related entries

• Plural-component spray
• Proportioner troubleshooting
• Spray equipment maintenance
• Cold weather coating
• Impingement mix spray guns (new)
• Polyurea spray rigs (new)