The article in TCI about spraying TALL trees said that using a #14 tip on the gun would hit 60-75ft with 200psi nozzel pressure.

We get metric tips , so from what I gather that is a 7.0mm. (HUGE)

I tried it , not very practicle. Pumped at about 35gpm!!! and didnt get 40ft, the biggest we curently use is 4.0mm.

SO where I'm going is; what are the biggest holes people find useful?

Reply to post by Sanborn, on June 16, 1999 at 21:43:09:

Based on a lot of experience, particularly in the Gypsy Moth years, I would not expect a #14 tip to hit 60-75 feet at 200PSI, at least not very often.

That said, there are a lot of variables, including: a) pump capacity (gpm), you're not going to do it with a 10 or 20 gpm pump, 35gpm or better for such big trees, b) pump pressure, our typical operating pressure for 35gpm pumps and big trees was 600-800psi. The literature will tell you that lower pressure results in larger droplet size which results in more height, that's not always been my experience, may relate to the following issues, c) effective pressure at gun, which relates mostly to hose length and diameter. Again the literaturre will tell you that the optimum set up over long lengths is a larger diamter hose nearer the pump and a smaller one nearer the gun. Most set ups today, particularly with low friction synthetic hoses, seem to be 3/4" pump to gun. The point is the longer the hose, the smaller the diameter, the more connections in the hose the more friction loss of pressure will be. d) tip diameter. The issue is capacity. At a given pressure a column of water of a given diamter will go to a certain height. Above a certain height the column can't support its own weight and starts to break up. A larger diameter column will support itself to a greater height. e) tip condition. A brand new tip has a hole through it which has clean edges with no nicks or imperfections around the entire circumference of the hole at both the top and bottome side of the tip or disk. The walls of the hole are perpendicular to the top and bottom surface of the tip or disk. As the tip is used metal is worn away, The edges become less that perfect and the walls of the hole are no longer perpendicular. This happens faster with dirty water and rust is also a problem. Any such imperfections cause the column of water to start breaking up as soon as it comes out of the tip. You can use hardened tips. Or just throw them away and replace as soon as you can observe the imperfections or you see fine droplets breaking away from the column of water near the tip. f) wind. You'll always do better in dead calm. It all falls off from there. See how much better you do in early AM or near dusk. g) surface tension of the water. There's not much in the literature on this but the lowere the surface tension of the water the smaller the size of a droplet that will hold itself together. Spray additives that are intended to reduce surface tension to help the coverage on the leaf (spreaders) may in fact result in smaller droplet size, reduced height and increased drift. Additives that enhance surface tension may have the opposite effect. It has been suggested that better height can be achieved when using oil sprays (than other materials) because of enhanced surface tension.

So experiment with NEW tip sizes and adjusting pressure to get the best result from your rig. Schedule big trees for early or late in day when wind is less a problem.

#12 and #14 were always are most common choinces for large shade trees. Occassionally a # 16 was used, generally to overcome wind. Yes those big tips pour out material. Crews don't always like to bother but think about switching tips during an application. Use a big tip for big stuff and smaller tips for smaller stuff. Don't go any bigger than needed to reach the material you're spraying. Sounds like a bother but you may find that a big tip uses less material than standing there for half an hour trying to get that small tip to reach up there and the smaller tips save you enough material and time in going to refill the tank to more than make up for it. I always carried a wrench and an assortment of tips in my back pocket.

Good luck.

Reply to post by Scott Cullen, on June 16, 1999 at 21:43:09:

I left out an additional group of factors, h). There's a phenomenon I'll call "build" for lack of another term. If you can hold the stream steady there is a "build" effect and it will gradually increase height to its maximum. Supposedly like a race car or bike "drafting" behind the car in front. Or (with your 9 years in the corps you probably know this better than I) the first round from an automatic weapon goes farther than the first, the third farther than the second etc. as the succeeding rounds take advantage of the low pressure area behind the preceding round.

There's also the issue of interior branches and foliage physically interfering with the stream. While lower pressure may theoretically give you more height (as discussed above) more pressure is sometimes needed to "punch through" the interference.

And finally, you can sometime work with a light wind to loft the spray stream and carry it on to the target.

Reply to post by Scott, on June 18, 1999 at 06:42:58:

Thanks for the refresher, I puts together things I've read or noticed, like the spray coming from an eroded tip, I've noticed "build" too.

Some of our smaller pumps we have to use the surge of pressure the builds up in the line.

Our guys carry two or three tall tree guns with various tips and a JD-9C. We use quick connects on the hoses. I know waht you mean about using a small tip on a big tree, Ive been stuck with a 2.5mm whan my bigger one sprung a leak. I couldnt get a wrench in the plastic thing on the end so I was stuck till I came a cross one of our pruning crews. I found a Sthil scrwench fits good'nugh.