Comparison of Siphon and Pressure Sandblasting Systems

A Brief Overview
by
Jess Pulliam

There are two basic types of sandblasting systems found on the market today, Siphon Fed and Pressure Fed systems.  Although both types can be used for sandcarving there are differences in the capabilities and efficiency of the two types.  There is also a price differential in the two types of systems.  Understanding the differences and capabilities before purchasing your first equipment can help eliminate mistakes and disappointments.

Siphon Feed sandblasters are the most basic of all existing sandblasters on the market today.  A siphon feed sandblaster works on the principal of high volume and high pressure air passing through a venturi, which causes a suction and that resulting suction sucks media through a feed tube to the nozzle.  A reduction of pressure or volume adversely effects the efficiency of the system.   The advantages of a siphon feed sandblaster are the low start-up cost and (if using a blasting cabinet) the continuous recycling of blasting media eliminating the need to refill. Disadvantages of siphon feed systems are that it is a slower sandblasting system.  Siphon fed systems use air less effectively because a large volume of air is required to suck the abrasive material from the bottom of the hopper or cabinet to the nozzle.

Below is a diagram showing the principal behind a siphon blaster handle/nozzle.

Siphon blasters come in all sizes and styles, but the principal of operation is the same for all of them.  Below are some examples of different types of siphon fed blaster systems.

Hand-held gravity feed siphon blaster. Inexpensive blasting nozzle with hose and tube to drop into a bucket of media.
   
Portable Siphon Blaster with integrated media hopper. Media is poured into open hopper and hose connects to venturi on bottom of hopper. Cabinet siphon blaster.  Tapered area on bottom of cabinet is media recovery/reservoir and media hose sucks media from there, recycling it inside cabinet.

A siphon fed sandblasting system may be a good choice if you are typically doing low production runs or require specialized sandblasting techniques.

 

Pressure Feed sandblasters are very effective for larger production runs and, on an average blast four times faster than a siphon fed system.  Their use of compressed air is much more efficient and enables you to blast your items quicker and at lower pressures.  A pressure fed sandblaster utilizes a Pressure Pot to pressurize the abrasive media before it mixes with the air in a mixing chamber instead of relying on suction created by a venturi to suck the abrasive media into the airflow and out the nozzle.  The media is forced into a media mixing chamber under a higher pressure than what you are blasting at.  The air coming from the compressor into the media mixing chamber passes through a regulator before entering the mixing chamber, lowering the pressure (and resulting volume) at the nozzle.  The media enters the mixing chamber after passing through a media valve.  Air pressure/volume and media flow are independently controllable. This allows more efficient blasting with a lower pressure, yet maintaining a consistent volume of abrasive in the air.  Pressure fed sandblaster systems provide excellent control for all sandblasting applications and their efficiency reduces overall blasting times. Lower air pressure / volume also means the compressor will typically run less and the resulting air will not be heated as much, resulting in less condensation in the lines (although a dryer is recommended in ALL situations).

The main drawback of pressure fed sandblasting systems is the higher cost when compared to siphon systems. One factor to consider when selecting a pressure fed system is the size of the pressure pot where the abrasive media is stored. The size is determined by the number of pounds of abrasive it can hold.  The larger the pressure pot, the longer you can blast between refills.

The diagram below shows how the mixing chamber of a pressure pot works.  For details on how a pressure pot works, see HERE:

 

Pressure Feed sandblasting systems come in multiple sizes/styles also, but as with the siphon feed systems, the principal of operation is the same with all of them. Below are a couple examples of pressure fed systems.

A typical Pressure Pot with pressure regulator and foot valve A sandblasting cabinet with a separate pressure pot and a foot valve.
   
 
A sandblasting cabinet with an integrated pressure pot built into the bottom of the cabinet with a dust collector.  

If you are working on a budget, siphon fed sandblasting cabinets can be converted to a pressure fed system by removing the existing siphon and hose, and passing the output hose from a pressure pot through the hole in the cabinet where the air feed line was originally.