Air powered sprayer

BTDT · Oct 4, 2006

I have a friend who took a 20" x 6ft pipe, welded the ends shut, put an axle under it, welded on a hitch, and wa-la, portable sprayer. He pressures it up with 12volt air compressor. It has pick up tube attatched to hose with spray handle, and pipe nipple with cap on bottom back end for drainage. Maybe someone could use this idea. He pulls his behind tractor, but you could use smaller pipe and customize for lawn tractor.

PineRidge · Oct 5, 2006

How about a few pictures to get our adrenaline flowing?

rambler · Oct 6, 2006

Metal is not a good idea for many sprays, esp Roundup & other glysophate products.

I'm not real comfortable with a pressurized home-made vessel full of chemical behind me either. Hope there is a blow-off valve on it.

I'm a farmer, need to take the course & pass the test every 3 years to apply herbicides. This project sounds like a person should know what they are doing.......

--->Paul

Highbeam · Oct 6, 2006

Sounds like a grenade. Those little compressors can get 75 psi in there. a 20" pipe has an end area of 314 square inches so there will be 23,561 lbs of force trying to blow that end cap off. It won't just go phud either, the compressed air will continue to expand and blow the shrapnel.

No way jose.

BTDT · Oct 8, 2006

Thanks for the reply's. Not trying to get anyone hurt here, just passing on some ideas of things I have seen and heard that other folks have done. Air is just what he used to power sprayer. More info: He is certified welder for the gas co., pipe was high pressure gas pipe left over from job. I think he has a guage and schrader valve that he uses to air up (like putting air in tire). Doesn't take much pressure to operate. I guess you would have to be careful with type of chemicals used, and you could put 12volt pump like on some of Tractor Supply's sprayers to operate.

rambler · Oct 8, 2006

Sounds like your friend at least understands pressurized vessels.

The other problem with it is that you get no agitation at all. Most spray solutions tend to settle out. With a pump on a sprayer, it recurculates the spray & keeps the chemical mixed.

--->Paul

BTDT · Oct 8, 2006

I guess pulling it around behind tractor/atv/truck and it bouncing around keeps it stirred up. I haven't asked him about that. But if you have ever tried to carry an open topped 5 gal. bucket of water anywhere you know how it spashes everywhere.

rambler · Oct 8, 2006

Again, I'm used to 300 gallon or bigger spray tanks, and mixing 2-5 things in the tank, & the label requiring me to agitate for 15 minutes & I legally need to follow the label - the county does stop in & check on us farmers often enough to keep us somewhat on our toes.

Different world for me.

It just sits in the bottom if I don't agitate it.

--->Paul

6or7dazeaweek · Oct 9, 2006

I'm a farmer, need to take the course & pass the test every 3 years to apply herbicides. This project sounds like a person should know what they are doing.......

--->Paul[/QUOTE]

Not to get off course, but the certification and costs involved in applying chemical pesticides is why I have decided to go organic. Yup, it's more costly but in the long run, I'm more comfortable with it.
Jon

HomeBrew2 · Oct 9, 2006

Highbeam said:
Sounds like a grenade. Those little compressors can get 75 psi in there. a 20" pipe has an end area of 314 square inches so there will be 23,561 lbs of force trying to blow that end cap off. It won't just go phud either, the compressed air will continue to expand and blow the shrapnel.

No way jose.

Umm, a couple of things sound mighty funny there but maybe I'm not thinking right again ... I assumed he was talking about one of those little tiny 12V emergency air compressors that we keep in our cars for pumping up a tire. If so, it takes me 3 hours to go from flat to 15 psi in a 33x12.5x15 tire ... I wonder how may DAYS it would take to fill that 20" x 6' pipe to 75 psi.
But, even if it could pump to 75 psi in that size container in a time frame relative to spraying, isn't the psi calc you made on the end caps only valid if the tank was completely full and the pressure was applied with a fluid in a sealed system ... as in a hydraulic circuit?
I think the rig is plenty safe and cool idea.

Highbeam · Oct 10, 2006

"even if it could pump to 75 psi in that size container... isn't the psi calc you made on the end caps only valid if the tank was completely full and the pressure was applied with a fluid in a sealed system ... as in a hydraulic circuit?"

Doesn't matter if it is full or partially full of liquid or air. The pressure will be marginally higher at the bottom if filled with liquid due to the weight of the liquid. It also doesn't matter whether it is sealed or not but if it is not sealed then the pressure will bleed off. I wouldn't buy a compressor that couldn't do 75 psi since the tire ratings are based on max pressure which on a 10-ply tire is way over 50, sorry I don't recall the actual. It might take all day using one of those cheesy compressors but being tractor type folks I am sure that someone along the line will hook it up to their shop compressor.

Good welds by a good welder and proper materials can withstand the forces. A guy like me with a stick welder who knows how to make the welded joints look good but maybe not make good enough welds is the scary part. If you are careful about pressures then you can spray with much lower pressures but you've got to figure that if there's a schrader valve that someone will fill er up.

HomeBrew2 · Oct 10, 2006

Highbeam said:
........

Let's see if I can keep you on point ... can you explain where your figure of 23,561 psi came from in your original post, in the context of this thread where compressed air is charging a tank with some water in it?
Your calcualtion is correct for a specific hydraulic circuit but not for an air charged vessel.

Tom_Veatch · Oct 10, 2006

HomeBrew2 said:
... can you explain where your figure of 23,561 psi came from in your original post, in the context of this thread where compressed air is charging a tank with some water in it?
...

Total force trying to separate the endcap from the body tube is equal to the pressure on the endcap X the area of the endcap.

F = PA
P = 75 psi
A = Pi X Radius Squared = 3.14159 X (10)^2 = 314.159

F = 75 X 314.159 = 23561.925 Pounds

Could also be stated as 375 Pounds per inch of circumference (weld length)

In a static situation it doesn't matter whether the pressurized fluid is a gas such as air or a liquid such as water or hydraulic fluid, the physics of the situation is the same.

If the fluid is in motion relative to the container wall, compressibility and viscosity of the fluid could have a big influence on the flow dynamics. But in a static situation such as this, it makes no difference at all.

bucmeister · Oct 10, 2006

I disagree with the 23,561 psi figure also. The figure is 75 psi as stated in the original point, that is the definition of psi, pounds per square inch afterall you can't extrapolate and focus that to predict failure. If that were the case then many hydraulic hoses and cylinders would explode everyday. Now as was later stated there is a concentration of force at the weld union where you have welded the joint with 7018 rod which has a strength rating of 70,000 psi so I think it will likely be able to handle the 375 psi mentioned later in the post.

Tom_Veatch · Oct 11, 2006

I don't think anyone is claiming a pressure of 23561 PSI. The pressure is only 75 pounds per square inch.

The units on the 23561 figure is POUNDS, a unit of force, not PSI, a unit of pressure. The force on each square inch is 75 pounds. The total force exerted over all 314.159 square inches of the endcap is 23561 pounds or 375 pounds per inch of weld.

The force we are talking about here is the total force necessary to hold the endcap in place against 75 pounds acting on each square inch of the endcap's area. That equates to a FORCE of 375 pounds distributed along each linear inch of weld. That says nothing about the stress in the weld or the likelihood of failure. It simply states how much force each linear inch of the weld around the circumference is required to withstand.

Or, think of it another way. What if you had a hydraulic cylinder that was 20 inches in diameter and a system pressure of 75 PSI. How much "push" would you expect to get from that cylinder when it extends? That's right, 23,561 pounds.

HomeBrew2 · Oct 11, 2006

Tom_Veatch said:
I don't think anyone is claiming a pressure of 23561 PSI. The pressure is only 75 pounds per square inch. ....

Thanks, Tom, for straightening this out. I have to admit I got caught up in Highbeam's overblown "grenade" analogy. Nobody originally talked about that kind of pressure nor using a shop compressor or anything else that would pose a serious threat.

Highbeam · Oct 11, 2006

Thanks Tom for clarifying, that was my math too. Lbs of force is not a pressure.

Pressure (liquid or air) applied over a certain area gives a force. I don't really know where the grenade will pop, I just don't want to be too close.

Highbeam · Oct 12, 2006

When we put watermains together we do a pressure test on them. A 12" ductile iron watermain, 250 psi, and a non-welded cap, and push together gasketed joints. You can bet that there is a huge thrust block holding the whole mess from blowing apart.

HomeBrew2 · Oct 12, 2006

Highbeam said:
When we put watermains together we do a pressure test on them. A 12" ductile iron watermain, 250 psi, and a non-welded cap, and push together gasketed joints. You can bet that there is a huge thrust block holding the whole mess from blowing apart.

Now we're up to 250 psi ... man, you gotta get outta the city more often ...