How to Pick and Test an Airless Tip for the Coating
Why this matters
The tip decides how much paint leaves the gun, how wide a band it lays, and how fine it atomizes. Pick one too small and a thick primer will not form a pattern at any pressure the pump can make; pick one too big and you overload the pump, lay a film that sags, and burn through paint the bid never counted. A worn tip does both quietly: it sprays more paint in a narrower band every week until a crew is laying heavy stripes and blaming the paint. This card owns tip selection across the shelf: how to read the number, what limits it, how to test the pattern before the first wall, and when a tip is done. Pump types and the wider tip catalog live in 'Paint Sprayer Types + Tip Sizes Reference'.
Safety first: the tip is where injection injuries happen
An airless pump puts paint through the tip at pressures high enough to drive it through skin. An injection injury can look like a small puncture and still be a surgical emergency, because the paint spreads into tissue under the skin. If it happens, go straight to an emergency room, tell them it is a high-pressure paint injection injury, and bring the coating's safety data sheet.
- Never put a hand, finger or rag in front of the tip, and never spray with the tip guard removed.
- Engage the trigger lock whenever you are not spraying.
- Relieve pressure before you touch the tip: trigger lock on, pump switched off, trigger lock released, gun held metal-to-metal against a grounded waste pail and triggered until no paint flows, trigger lock back on, then the prime or pressure-relief valve opened per the pump's manual. Do this before changing a tip, clearing a clog, or cleaning the gun filter.
- Clear a clog by reversing the tip, not by poking it: with pressure relieved, turn the reversible tip to its clear position, spray into the pail, relieve again, turn it back.
- Spray mist is an inhalation hazard. Respirators are worn under a written program per 29 CFR 1910.134 (applied to construction by 29 CFR 1926.103), with fit testing and medical evaluation; a painter outside the program does not spray that day. Masking and overspray control are in 'Spray Containment and Overspray Control'.
Reading the number on the tip
REVERSIBLE TIP, stamped on the handle: 515
5 15
| |
| +-> orifice 0.015 in (fifteen
| thousandths) on most tips
|
+-> fan code: 5 x 2 = about 10 in wide,
measured about 12 in off the surface
same rule, other common sizes:
311 -> 6 in fan, 0.011 in narrow, enamel
515 -> 10 in fan, 0.015 in walls
517 -> 10 in fan, 0.017 in walls, primer
619 -> 12 in fan, 0.019 in large areas
The first digit doubled is roughly the fan width in inches at about 12 inches from the surface. The last two digits are the orifice diameter in thousandths of an inch. That convention holds on most tips; some makers code fine-finish and specialty tips differently, so check the tip maker's chart when a number does not decode sensibly.
What each half controls. The orifice sets how much paint flows. The fan width sets how wide a band that flow is spread over. Two tips with the same orifice and different fans deliver about the same paint, spread thinner on the wider fan. Two tips with the same fan and different orifices lay the same width band, heavier on the larger orifice.
How much the orifice matters. At the same pressure, flow scales roughly with the orifice's area, which goes with the square of its diameter. A 0.017 against a 0.015 is (17 x 17) / (15 x 15) = 289 / 225 = about 1.28, so roughly 28 percent more paint for the same pull of the trigger. Check from the other side: 225 x 1.28 = 288. That is why a one-step jump in orifice is not a small change.
The two limits that bound the choice
The coating maker's tip range. The product data sheet for a sprayable coating lists an orifice range, sometimes with a fan width and a recommended filter. Thin coatings (stains, enamels, lacquers) sit at the small end; heavier ones (high-build primers, elastomerics, block fillers) need larger orifices to pass at all. Pick within the range. Below it, the coating will not atomize into a clean pattern; above it, the film goes on heavier than the data sheet's film-build figures assume.
The pump's maximum tip rating. Every pump is rated for the largest orifice it can supply at full pattern, usually printed on the pump label and in the manual, often with a note for one gun or two. A tip larger than the rating starves: the pump cannot keep pressure up, the pattern tails return mid-stroke, and the motor runs flat out. Long hose runs eat into this, since pressure drops along the hose.
The usable tip is the overlap of the two: inside the coating's range and at or below the pump's rating. If there is no overlap, the coating needs a bigger pump, not a bigger tip.
Testing the pattern before the first wall
- Gun filter to match. Smaller tips need a finer gun filter, larger tips and heavy coatings a coarser one; use the pump maker's filter chart. A filter too coarse lets debris clog a small tip; one too fine clogs itself with a heavy coating.
- Tape a sheet of cardboard to a wall or stand it against a ladder outdoors, well clear of anything that should not get paint.
- Start at low pressure. Hold the gun about 12 inches from the cardboard, perpendicular to it, and spray a short horizontal pass. At low pressure the fan shows tails: heavy bands at the top and bottom of the pattern with a thin middle, because the paint has not been forced to atomize evenly across the fan.
- Raise pressure in small steps and spray a new pass each time. Stop at the lowest pressure where the tails close into an even band with soft, tapered edges.
- Measure the fan. At 12 inches, a new 515 or 517 should lay roughly a 10 inch band. Write the pressure and the width on the cardboard.
- Do not keep turning it up. Pressure above the point where tails close adds overspray and bounce-back, wears the tip faster and puts more mist in the air, without making the pattern better.
When a tip is worn out
The orifice is a carbide insert, and abrasive coatings erode it. As it wears, the orifice grows and its shape rounds off, so the tip sprays more paint in a narrower fan. The film in each pass gets heavier and the band gets narrower, so a painter who keeps the same walking speed and overlap lays stripes. Primers, elastomerics and anything with heavy pigment or fillers wear tips fastest.
The check is the same cardboard test: at the same distance and pressure, compare the fan width to a new tip of the same size. A tip that lays noticeably narrower than new, or needs the pressure turned up to close its tails, is done. Write the date on the tip box when you put a new one in service.
Worked example: an empty-house interior repaint
The job. A vacant three-bedroom house, walls going to an eggshell latex and doors and trim to a semi-gloss latex enamel, both sprayed. Illustrative figures, read from this job's documents: the wall paint's data sheet lists a tip range of 0.015 to 0.019; the enamel's lists 0.011 to 0.015; the pump label rates it for a 0.021 tip with one gun. Hose run 100 feet.
Walls. Both 515 and 517 sit inside the wall range and under the pump rating. The lead chose the 517 for the extra flow on long open walls, about 28 percent more than the 515 at the same pressure, which lets a sprayer walk faster for the same film. A new 517 went on with the pump maker's recommended filter for that orifice.
The test. On cardboard at 12 inches, tails were plain at the low setting, still visible at the next step, and closed at the third, where the pump gauge read about 1,800 psi (your number will differ with the coating, its temperature and the hose length). Fan measured at about 10 inches. Pressure was left there.
The tip that failed the test. The crew's spare 517 from the last job measured only about 7 inches wide at the same 12 inches and the same pressure, against 10 inches for the new one, and its band was visibly heavier. That is a 3 inch loss, 30 percent of the new width. It went in the trash. A sprayer using it at the new tip's walking speed would have laid a heavier, narrower stripe and lapped badly between passes.
Doors and trim. The lead swapped to a 312 (6 inch fan, 0.012 orifice), inside the enamel's 0.011 to 0.015 range. Pressure relieved before the swap, per the steps above. The narrow fan suits door stiles and casing, where a 10 inch fan would put half its paint in the air. Tested on cardboard again, because the right pressure for a different tip and coating is a different number.
What came next. The wet film from the first wall was checked with a gauge against the data sheet's figure; how that check is done belongs to 'Film Build and Wet Film Thickness Verification', and the coverage arithmetic behind it to 'Spread Rate, Wet Film and Dry Film: The 1604 Number'.
What would change the answer. A high-build primer whose data sheet called for 0.021 to 0.025 would sit above this pump's 0.021 rating at all but the bottom of its range. The answer there is a pump rated for the tip, not forcing a starved pattern.
References
- 29 CFR 1910.134, Respiratory Protection
- See related: Paint Sprayer Types + Tip Sizes Reference
- See related: Spray Containment and Overspray Control
- See related: Film Build and Wet Film Thickness Verification
- See related: Spread Rate, Wet Film and Dry Film: The 1604 Number