Choosing The Right Blast Nozzle

There's a balance to be achieved when choosing a nozzle, and it starts with your air compressor. After you understand how the size of your compressor affects your production rate, you'll need to consider nozzle size. If you choose a nozzle with a narrow bore, you'll sacrifice some blasting capacity. On the flip side, you won't be able to blast effectively if the bore is too large.

The nozzle's design comes next. Straight bore and Venturi are the two most common nozzle shapes, each with many size and pattern variations. Finally, you'll need to think about the nozzle's liner material. Durability, impact resistance, and cost are the three most important elements to consider when choosing the right nozzle bore material.

Nozzle Size

The most commonly-used nozzle sizes range from a 3/8" inner diameter to 3/4", increasing by increments of 1/16". A 3/8" nozzle is sufficiently constricted to produce an effective blast pressure with a 185 CFM compressor. A 1/2" nozzle is sufficient to produce an effective blast pressure with a 375 CFM compressor.

It’s important to note that when you 2X the diameter of the orifice, you 4X the size of the orifice and the volume of air and abrasive that can pass through the nozzle.

To find your optimally productive nozzle, start by determining what nozzle pressure (PSI) you need to maintain for productive blasting, and what volume of air your available compressor can supply per minute (CFM), then consult the following chart to find the nozzle orifice size that meets those parameters.

CFM (Cubic Feet per Minute) Required by each nozzle

Keep in mind that your compressor will produce less pressure at the nozzle than what is indicated on the chart, depending on the condition and configuration of your equipment.

nozzle size cfm chart

Nozzle Shape

Nozzles come in two basic shapes: straight bore and Venturi, with several variations of Venturi nozzles.

STRAIGHT BORE:

As compressed air enters the converging (left) end of a straight bore nozzle it accelerates, accelerating the abrasive particles suspended in the flow. The particles exit the nozzle in a tight stream and produce a narrow, concentrated blast pattern upon impact.

 straight bore nozzle

BLAST NINJA QUIET NOZZLE:

  • Blast Pattern: 3" at 18" distance
  • Production Rate: 5/5

New proprietary design leveraging the same principles for reducing jet aircraft engine noise. The design reduces abrasive blasting noise without affecting production rates.

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LONG VENTURI:

  • Blast Pattern: 3" at 18" distance
  • Production Rate: 4.5/5

long venturi nozzle

Venturi nozzles feature a converging entry, and a diverging exit. This shape is designed to produce an effect which greatly accelerates the air flow and particles– it is not, however, the Venturi effect.

The Venturi effect is an observation that when an air flow accelerates while passing through a constriction, there is a corresponding drop in pressure.

This is not the key principle at work in a “Venturi" nozzle. Technically, these nozzles are de Laval nozzles, the same design featured in jet exhausts. The rapid acceleration of the air flow and particles in a de Laval nozzle is due to an effect that occurs as the flow breaks the speed of sound.

Besides producing tremendous acceleration, the angled shape of the diverging end spreads out the flow, producing a large blast pattern and a more uniform particle distribution than a standard bore nozzle.

Long Venturi nozzles produce up to 40% better production rates and consume less abrasive compared to straight bore nozzles.

DOUBLE VENTURI:

  • Blast Pattern: 3" at 18" distance
  • Production Rate: 4/5

double venturi nozzle

A double Venturi nozzle is a de Laval nozzle with an extra wide exit opening and holes at the diverging end.

According to the Venturi effect, as the velocity of a flow increases, the pressure drops, creating a vacuum between the shockwave and the throat, reducing abrasive velocity. With a double Venturi nozzle, atmospheric air is drawn through the holes into low pressure area, expanding the air flow to produce a wider blast pattern.

WIDE THROAT:

  • Blast Pattern: 3" at 18" distance
  • Production Rate: 5/5

wide throat nozzle

Wide throat nozzles are de Laval nozzles with a wide throat and an extra-1/4" wide converging section. When used in conjunction with a hose with matching inside diameter (and with a corresponding air volume increase), the wide throat nozzle can enhance productivity up to 15% over long Venturi.

XL PERFORMANCE:

  • Blast Pattern: 5" at 48" distance
  • Production Rate: 3/5

xl performance nozzle

These extra-long nozzles accelerate particles over a longer distance, achieving higher exit velocities, allowing the blaster to stand further back from the surface being blasted, and producing a larger blast pattern and higher production rates. 

NOZZLE MATERIAL

The third consideration when choosing a nozzle is the composition of the lining inside the bore. Harder materials will be more resistant to wear, but are more expensive to replace and are prone to cracking under rough handling. There are three basic types of carbide nozzles.

TUNGSTEN CARBIDE:

  • Durability: 1/5
  • Impact Resistance: 5/5
  • Price: Low

This is the least durable of the carbide nozzles, but relatively cheap and resistant to impact. Suitable for blasting slag, glass and mineral abrasives.

 SILICON CARBIDE:

  • Durability: 1/5
  • Impact Resistance: 5/5
  • Price: Low

Impact resistant and durable like tungsten carbide, but lighter. Causes less operator strain.

BORON CARBIDE:

  • Durability: 3/5
  • Impact Resistance: 1/5
  • Price: High

Extremely hard and durable, but brittle. Up to ten times the longevity of tungsten carbide.

COMPOSITE CARBIDE:

  • Durability: 5/5
  • Impact Resistance: 3/5 
  • Price: High

Some manufacturers produce their own composite carbide nozzles, which are even harder than boron carbide so keep that in mind. Also, research has shown that blast productivity gradually increases with abrasive feeding rate until a critical value is reached, after which productivity maintains constant. So after that value has been surpassed, consuming more media actually reduces particle velocity, wastes abrasive and lowers efficiency.