Bead Blasting

 Blast cleaning uses abrasive grit (glass beads, steel shot, sand, even dry ice) powered by compressed air through a jet to the surface being cleaned. Blasting can be used for cleaning, controlling surface roughness, preparing a surface for application of coatings and paint,  or carving a design onto a surface. Castings can be coated with mold sand which can easily be removed by blasting. Graffiti or old paint can quickly be removed from the side of buildings with blasting.

Sand blasting machines are usually designed to operate on air at a pressure of 90-150 psig. The size of the nozzle aperture determines the air flow needed by the machine. Small nozzles are more appropriate for fine work with large nozzles used for gross material removal.

Recently, companies have been offering systems designed for micro bead blasting. These systems are desktop machines useful for cleaning off small parts. Some have been used to replace dental drilling.

Dry ice is a fantastic bead blast material as it sublimes and leaves no messy clean up of the beads.

All bead blasting processes can benefit from clean dry air. If the material is hydroscopic, like baking soda, the air should be at a reduced dewpoint to prevent caking. 

How to drain liquids at high pressures

Occasionally customers have high pressure compressed air or natural gas lines that need to be filtered to remove oil and water contamination. The problem is, how do you drain out the accumulated liquids? Most automatic drains have a maximum pressure of 150 psig (10 bar), well below the pressure of the filtration vessel. Attaching a valve to the drain could create a dangerous situation. In the diagram above, draining is accomplished by utilizing two valves and a small receiver tank rated at the same pressure as the filter vessel. The receiver could even be a length of pipe as long as its volume is sufficient to hold the amount of liquid that is expected to accumulate between draining. The draining is manual. Initially, the valve closest to the filter vessel is left open to allow liquids to drain into the receiver and must be accomplished by closing the top valve near the filter vessel and opening the bottom valve slowly. It is important to open the bottom valve slowly and carefully because the receiver is at operating pressure. Naturally safety gear like goggles, etc. should be worn.

Compressed Air Usage in the Beverage Industry

Soda bottlers and brewers depend on compressed air for a number of bottling operations, including capping bottles and kegging beer. The immediate, sensitive response of compressed air makes it the choice of power on many types of controls in production processes. Transferring liquids from cask to cask, unloading grain from cars and hoisting it to storage bins, and testing kegs for leaks are other operation for compressed air. Automatic bottling machines have many applications for compressed air in control and in actuating some of the necessary reciprocating and intermittent motions. Air that comes incontact with the beverage or to blow out the container or bottle should be filtered with Sterile Air Filters.

Compressed Air Usage in the Airline Industry

My next few posts will focus on industries and their use of compressed air. My reference  for these entries is the Compressed Air and Gas Handbook.

Several hundred thousand rivets are used in the manufacture of an airplane or helicopter. Powerful, lightweight, air operated drills, wrenches and riveting Hammers are used in the assembly of plane fuselages, wings and other components. Airplanes provide many applications for compressed air in addition to those used in the manufacturing stages. Compressed air stored in the air springs of the landing gear softens the shock when the airplane lands or is taxiing. Cabins are pressurized and air conditioned for high-altitude flights. Compressed air is used for de-icing plane wings, for heating the engines, for various actuating and control functions, and for operating the refueling equipment. The modern safety devices such as life rafts, and emergency chutes are inflated quickly and reliably by compressed air or gas stored in high pressure cylinders.

Compressed air is also used to start jet engines and to provide cabin service for the comfort of passengers while the plane is at the terminal.

What is a drip leg and why do I want one?

Compressed air systems are best designed to be resilient to system upsets. It is not uncommon for a slug of water and oil to make its way down a line. If that slug makes it to your equipment you’re in for downtime and unscheduled maintenance. Depending on the equipment, you’ll want to install coalescing filtration and in some cases a membrane air dryer to guarantee that your equipment sees dry air. However, if and when that unexpected system upset occurs, you don’t want to overwhelm your filters or dryer. No matter how good the coalescer is, a drip leg before it will assure the filter’s proper operation.

To install a drip leg, come off the top of your feeder supply line from the top of the pipe as I explained earlier. Then drop the line 2 – 3 feet (1 meter) below the inlet filters. At the bottom of this pipe install an automatic drain to remove built up water and oil. At the height of the filters, install a tee to direct the air to the filters and your equipment. A drip leg like this is an added layer of protection from oil and water that is very inexpensive to install.

Here is an example of a drip leg configuration: