Blasting Hose

10.10.2.5 Blasting Hose

There are two types of abrasive supply hoses:

• Four-ply - use when the hose is subject to external abuse or when there is danger of the operator pulling it at right angles

• Two-ply - a lighter hose some blasters prefer because of its greater flexibility

The size and length of abrasive blast hoses are related to their efficiency. A rule of thumb is: the hose ID should be three to four times the size of the nozzle orifice.

The whip length section is the last section of the blast hose. It gives the operator (blaster) better handling and enhances his ability to handle the hoses under high pressure. It is usually 10-15 ft (3-4.5 m) long and a smaller diameter than the rest of the blast hoses. The smaller ID causes a drop in pressure so it is recommended that operators use a whip attachment only when necessary.

Most blast hoses are now made with an internal ground; loading the hose rubber with carbon black allows static electricity to drain to earth. Sometimes an additional external ground is necessary. Use only grounded hoses to ensure operator safety.

Couplings ( Figure 10.57 ) connect the hose sections. Using only externally fitted cou- plings is highly recommended. Internally fit- ted couplings reduce hose ID and air

capacity significantly. In addition, a turbu- lent condition may occur at the point where the air and abrasives hit the leading edge of the nipple inside the hose, resulting in pres- sure drop and heavy wear at that point.

Figure 10.57 Coupling

Couplings are held in place with external screws that penetrate into the wall of the hose. Ensure the screws do not penetrate the tube causing air leaks and loss of pressure.

Maintain grounding through the coupling. Because of inevitable pressure drops within air lines, keep pressure hoses as short as pos- sible. Preferably, the blast hose (from pot to blast nozzle), should not be more than 20 ft (6 m) long. When longer lengths are unavoidable, keep the hose straight; ensure any bends are wide and have a smooth radius.

During blast cleaning, the air compressor must be able to deliver and maintain the required air volume and pressure at the noz- zle. Related equipment, including the fol- lowing, must be of the correct size and type to match the compressor output ( Figure

10.58 ): • Air and abrasive hoses

• Hose couplings • Blast nozzles

Surface Preparation 10-31

(known as a receiver) or directly to the item that requires it.

Producing compressed air presents two problems to the surface preparation process. These are:

• Any change in atmospheric pressure can result in the release of water vapor from the air.

• Because compressed air in the receiver is stored by pressurizing an oil reservoir, it is possible that oil vapor remains in the air as it is released.

Both of these factors require fitting adequate

vapor traps to blast cleaning equipment to The compressed air must be free of contami-

Figure 10.58 Air Compressor to Pot Connection

remove oil and water contaminates. nants, including oil and water. First, since