Popular Woodworking 2006-02 № 153, страница 98

Popular Woodworking 2006-02 № 153, страница 98

Fan-width control knob

Fluid

control

knob

Needle-packing nut (needle packing inside)

Gun body (or handle)

Horn

just in front of the trigger) that is dry or too loosely compressed by the needle-packing nut, or an untightened or damaged fluid nozzle. Check the tightness of the needle-packing nut and fluid nozzle, and if this doesn't solve the problem, oil or replace the needle packing or replace a damaged fluid nozzle.

• An obstruction in the fluid passageway may also allow air to enter the fluid stream. Try "backflushing" the passagway by pressing your finger over the center hole of the air cap while spraying a short burst. If this doesn't remove the obstruction, take the gun apart and do a thorough cleaning.

Dripping from the Front of the Gun

The cause of fluid (stain or finish) leaking from the tip of the fluid nozzle at the front of the spray gun is the fluid needle not seating well in the fluid nozzle.There are a number of possible causes. Here are the most common in rough order of their frequency.

• The packing that surrounds the fluid needle may be squeezed so tightly by the needle-packing nut that it prevents the needle from moving freely. Loosen the nut a little.

• The needle packing may have dried and hardened to the point that it doesn't allow the needle to close tightly. Lubricate the needle packing with a non-silicone oil such as mineral oil. Apply the oil to the fluid needle and

To get an even coating using a spray gun, the spray pattern should be an elongated oval that is even from end to end.

If the spray pattern is bunched up in the center even with the spray-gun controls wide open, there isn't enough air pressure for the viscosity of the liquid. Increase the air pressure (if your air is supplied by a compressor) or thin the liquid.

move it back and forth several times with the trigger, or remove the needle and needle-packing nut and apply several drops of oil directly to the packing.

• There may be dirt, paint or finish stuck in the tip of the fluid nozzle that prevents the fluid needle from seating fully. Clean the fluid nozzle.

• The tip of the fluid nozzle or the tip of

If the spray pattern is heavy on the ends and light in the middle (called a "split" pattern), there is too much air pressure for the viscosity of the liquid. Reduce the pressure or add less thinner.

If the spray pattern is heavy at one end, there is an obstruction in the fluid nozzle or air cap, or one of these parts is damaged. Clean the gun. If this doesn't solve the problem, the damaged part must be replaced.

Dripping from the tip of the fluid nozzle is caused by the fluid needle not seating well in the fluid nozzle. Follow the suggestions in the text to identify the source of the problem. Dripping from the needle-packing nut (just in front of the trigger) is caused by the needle packing not sealing well around the fluid needle. Check that the needle-packing nut is well tightened and that the needle packing is lubricated.

the fluid needle may be badly worn or damaged, which prevents proper seating. Replace the damaged part.

• The spring that pushes the fluid needle closed may have weakened or broken. This spring is located just inside the screw-knob on the back of the gun that controls the fluid needle. Replace the spring.

• The fluid needle may be too small or too large for the fluid nozzle, which prevents proper seating. Change parts so the two seat well. Fluid needles and nozzles are sold as sets meant to work together. You can buy them from the manufacturer of your spray gun.

Dripping from the Packing Nut

If the needle packing isn't sealing well around the fluid needle, fluid will pass through and drip from the needle-packing nut. There are two possible causes.

• The needle-packing nut may not be screwed on tightly enough to press the needle packing into contact with the needle. Try screwing this nut tighter (but not so tight that it interferes with the easy movement of the needle).

• The needle packing may be worn or dry. First, try lubricating the packing with a non-silicone oil such as mineral oil. If this doesn't work, replace the packing with a new one, which you can get from your spray-gun supplier or from an auto-body supply store. PW

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