DeVilbiss HVLP Gravity Feed Spraygun Spécifications télécharger pdf (Page 6)

PART IDENTIFICATION

FUNCTION

9. What are the principal parts of

a spray gun?

Figure 8 - Spray Gun Anatomy

10. What happens when the

trigger is pulled?

The trigger operates in two stages.

Initial trigger movement opens the

air valve, allowing air to flow

through the gun.

Further movement of the trigger

pulls the fluid needle from its seat

at the fluid tip, allowing fluid

material to flow. When the trigger is

released, the fluid flow stops before

the air flow.

This lead/lag time in the trigger

operation assures a full spray

pattern when the fluid flow starts.

It also assures a full pattern until

the fluid flow stops, so there is no

coarse atomization.

11. What is the function of the

air cap?

The air cap (see figure 10) directs

compressed air into the fluid

stream to atomize it and form the

spray pattern. (see Figure 9)

Round Tapered Blunt

Figure 9 - Types of Spray Patterns

There are various styles of caps to

produce different sizes and shapes

of patterns for many applications.

12. What are the advantages of

the multiple jet cap?

This cap design provides better

atomization of more viscous

materials.

It allows higher atomization

pressures to be used on more

viscous materials with less danger

of split spray pattern.

It provides greater uniformity in

pattern due to better equalization

of air volume and pressure from the

cap.

It also provides better atomization

for materials that can be sprayed

with lower pressures.

Figure 10 - Multiple Jet External Mix

Air Cap

13. How should an air cap be

selected?

The following factors must be

considered:

a) type, viscosity and volume of

material to be sprayed

b) size and nature of object, or

surface to be sprayed (multiple, or

larger, orifices increase ability to

atomize more material for faster

painting of large objects).

Fewer, or smaller orifices usually

require less air, produce smaller

spray patterns and deliver less

material. (These caps are designed

for painting smaller objects and/or

using slower speeds)

c) material feed system used

(pressure, suction or gravity)

d) size of fluid tip to be used (most

air caps work best with certain fluid

tip/needle combinations)

e) volume of air in cubic feet per

minute (cfm) and pressure in

pounds per square inch (psi)

available.

See the DeVilbiss spray gun

catalog for proper selection of

air cap / fluid tip / needle

combinations and typical uses.

14. What is the function of the

fluid tip and needle?

They restrict and direct the flow of

material from the gun into the air

stream. The fluid tip includes an

internal seat for the tapered fluid

needle, which reduces the flow of

material as it closes.

(see Figure 11).

The amount of material that leaves

the front of the gun depends upon

the viscosity of the material, the

material fluid pressure and the size

of the fluid tip opening provided

when the needle is unseated from

the tip.

Fluid tips are available in a variety

of sizes to properly handle

materials of various types, flow

rates and viscosity.

Figure 11 - The Fluid Tip and

Needle

2. Air Atomizing Spray Guns (Cont’d)

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