When our sprayer pressure does not come up, or takes a while to reach the setting, we blame the pump, when in many cases the problem is in the line leading to the pump.

A sprayer designed and built with some degree of engineering has a filtering system between the tank and the pump, and that system is sized in line with the suction capabilities of the pump. (I have seen sprayers built with no inlet line strainer – I have seen sprayers with undersized inlet lines and strainers)

The pump is the heart of the sprayer and needs to be protected. An undersized strainer and/or inlet line will cause high suction vacuum and put a strain on the inlet side of the pump very much like what Arteriosclerosis and clogged arteries will do to our own hearts. And so will a clogged strainer.

The rule of thumb for inlet lines and strainers is that they be of a diameter equal or greater than the suction end of the pump. Also look at the bulkhead fitting in the bottom of the tank where the suction line attaches and the shut-off valve right after it, these must also be that same size..(there should be a shut-off installed between the tank and strainer so that you can do maintenance work even with a full tank).

Any bottleneck in this system will overtax the pump. If your sprayer has any of the design flaws mentioned above, correct them immediately.

Periodic, and I mean periodic maintenance of inlet strainers is critical to your pump.

Surfactant Problem

When you clean out the mesh in the strainer, look for clumps of spray material. This will tell you that you are not agitating correctly or that your materials are not mixing well with the water – a surfactant problem.

Correct those problems right away and you will have less strainer clogging.

Poor Filtering

Also, look at the screen and make sure it is not deformed as this would cause poor filtering. The holes in the screen should be slightly smaller than the smallest nozzle in your spray system. If your mesh is too tight – very small holes – replace it with a lower mesh number (the lower the number, the larger the holes_ 50 and 20 mesh screens are the most popular, but if you have very small nozzles -1 or 8001′s – you might need an 80 or 100 mesh filter). Selecting the correct screen will prevent nozzles clogs.

Poor Agitation

Poor agitation will also cause sedimentation of unmixed materials on the bottom of the tank. When the pump starts up these are drawn out all together and overload the strainer. Make sure you flush out the tank and spray lines after use and do not leave any sediment in the bottom or in the strainer.

When you reassemble the strainer, make sure the gasket is properly installed and in good condition. Many times I am called out to troubleshoot a pump and find the strainer is sucking air because the gasket is either not there, broken or crimped.

The pump would much rather pull air than water, because its easier and, when you have air in the system, you don’t have pressure or your pressure is erratic.

Odd Objects

Another thing to look for is a clog in your suction line. I have found labels, old rags, socks, poly bags, paper and all sorts of other things clogging the inlet lines usually between the tank and the strainer. One way to check this out is to remove the strainer bowl, open the valve and watch the flow. If it does not come out with force and volume, check for an obstruction.

When initially you have normal pressure and it drops off some 30 seconds to one minute after opening the nozzles, you have an inlet obstruction. Correct it immediately. High suction vacuum may not show itself the same way, but can go undetected until the pump breaks down.

Pump failure will be evident in piston pumps generally in the inlet valve area. The valve discs will break outwards (sucked out). Diaphragm pumps can also have inlet valve failure, but their most common breakage is in the diaphragms. These are literally pulled away from the piston head because of the vacuum. Roller and centrifugal pumps will show cavitation wear in the housings, and seal breakdown.

This can cause lower pressures out at the end of the boom and then your nozzles will not be putting out the same patterns and volumes as those close in.

Be logical and think in terms of an efficient irrigation system: always from larger to smaller until the end. Spend some time on it, look carefully, you may find an elbow, tee, fitting, close coupling, hose nipple, hose, filter, valve, anything that could cause that bottleneck. And it could be anywhere between the pump and the last nozzle.

Check the screen on all of your line strainers. Aside from making sure that they are not damaged or bent (which would certainly let large particles get by), check the screen size (mesh) and set them up as follows:

The strainer closest to the nozzles should have a screen size just a little smaller than the orifice of the nozzle. This will assure that particles that could lodge in the orifice and clog it do not reach the nozzle. Spray tip manufacturers recommend the mesh size for each of their tips. Check with your supplier for the proper combination.

If you have another strainer in line between the pump and the nozzles (and this is recommended) that screen size (mesh) can be one or two sizes larger than the last strainer.

And now to the main strainer. The one between the tank and the suction side of the pump.This one can have a screen as big as 16 mesh, which will allow the larger particles in the spray solution to recirculate and thus reduce the suction load on the pump. A fine mesh on this strainer will cause caking-up and blockage and will shorten the life of the pump. (the principal cause of diaphragm failure).

With this set-up, the other strainers down the line will take care of the filtering and, provided that the screens are in good condition, your nozzle blockage should be minimal. This type of filtering under pressure will break down particles in the solution, especially when using wettable powders, and allow them to be sprayed.

It does not make much sense to have such a large caliber hose carrying all that water when the nozzle at the end of the spray gun is only about 1/16" in diameter. So the hose really should be as small as practical without causing friction losses or bottlenecks.

Generally, the size of hose that works best for hand guns and spray wands is 3/8", 600 or 800 psi, depending on how you spray. This hose is not only cheaper than the 1/2", but also has better working and burst pressure factors. It is flexible and lightweight and, because it is carrying less water, not only is easier to handle while spraying, but gets less wear and tear through abrasion when being dragged along the ground, because of its lower overall weight.

Another bonus is that your can get up to 30% more hose onto on a standard reel, and, if you only have a rack to coil it on, that is also easier and lighter work. So look at your hoses; and the next time you have to replace them, think of going with a smaller size and lightening you or your employee’s load.

Generally, we just point them directly downwards or at right angles to the plant (in the case of laterals) and expect the fog they produce to travel in and out of the canopy and cover all the foliage on both sides.

If we make a big enough fog, this will be very true, but constraints on the amount of fog we can make in the future (drift) are going to cut into the efficiency of our coverage, which we took for granted, until now.

Aiming the nozzles so that their pattern penetrates the canopy will greatly improve our coverage and reduce drift. However, we cannot follow a rule-of-thumb on this except to try to get the spray to drive into the plants as low as possible at an angle which will make it "bounce upwards" and travel to most of the areas of the canopy, without producing great amounts of drifting fog.

Each crop has to be looked at with that in mind: how to get the spray down into the canopy before it becomes a fog.

One approach is to use narrow angle nozzles. These would be spaced closer to each other on the boom to make up for the loss of pattern produced by the wider angle nozzles, and the narrow pattern will propel the spray deeper into the canopy, especially if it is aimed forward at an angle of 35 degrees or less to horizontal.

The narrower pattern will travel farther before it begins to "break-up’ and, if you regulate your boom height accordingly, you should notice practically no drift or fogging above the canopy.

Putting more nozzles on the boom because of closer spacing will require you to use smaller orifices to maintain the volume. This you can calculate and calibrate yourself.

In order for this to work, you must use Disc/Core type nozzles. Get away from the Teejet type fan nozzles, they are for herbicides and banding, not for under-leaf coverage. The disc/core nozzles will give you angles as small as 15 degrees. (you have been used to 80 to 90 degree angles until now.)

We are giving you the basic idea and what to look for. It’s up to you to decide how you want to aim your nozzles, but please give it some thought.

All well designed sprayers have a pressure relief valve in the line coming out of the pump (pressure side). The pump produces a certain volume of liquid: pressure builds up when the outlet of that volume is restricted (the nozzle).

Pressure will continue to build up because there is less going out the nozzle than is being produced by the pump. In order to balance this, a relief valve will divert the extra volume so as to keep the pressure constant.

When the pressure in our sprayer drops, we usually blame the pump, but the first thing we have to look at is the wear in the pressure relief valve. The abrasives in our spray materials wear the seat and plunger in the valve and, when these do not seal properly, they will allow liquid to escape back into the return line.

Consequently, pressure cannot be built up because the relief valve is not restricting the flow because it is leaking. By checking out the relief valve first, we can usually save ourselves a costly and unnecessary pump repair as well as shorten down time, as relief valves are usually very simple to rebuild.

The relief valve is basically a plunger that sits in a seat and is held against that seat by a spring. The pressure in the line presses against that plunger and, when the pressure exceeds the pressure of the spring holding the plunger against the seat, the plunger is pushed away from the seat, allowing liquid to pass through.

The passing liquid then goes out through a line that takes it back to the sprayer tank. When the pressure drops, the spring pushes the plunger back against the seat. This system adjusts continually to maintain a steady pressure as set by the pressure on the spring, which is controlled generally by a screw/handle on the top of the pressure regulator.

A practical example is the pump that is producing 6 gpm for a spray gun using 2gpm, then the extra 4gpms are diverted through the seat of the relief valve, back into the tank. And this could be at any pressure, as long as the spring is strong enough to control it.

That is why we have pressure relief valves rated for 0-100psi, 100-300psi, 100-700psi, etc. Each one of these models has a stronger or weaker spring which generally can be adjusted within those pressure ratings.

Speaking of springs, this could be another cause for losing pressure. Some of these springs are corroded by the materials being by-passed in the relief valve and can weaken or even break and then yes, there will be no pressure at the nozzle.

So when troubleshooting loss of pressure in your rig, first look at the relief valve, (also known as control valve or unit). If the spring tensioning screw or adjustment is all the way down, chances are your failure is in this unit and not the pump.

Another item to look for is a hydraulic agitator (eductor) connected to the relief valve discharge line: This is not recommended for the following two reasons:

• The volume coming out of the relief port may not be constant, as it would change with variations in pump speed and number of outlet nozzles open. This could make the the operation of the agitator erratic, as there could be times when nothing is coming out of the relief discharge, therefore no agitation in the tank.
• The effect of the agitator (eductor) is similar to a nozzle, producing back pressure in the relief line. Some pumps, especially diaphragm pumps are affected by this back pressure, which could cause premature pump failure. Consequently, make sure that the relief circuit from the valve to the tank is not restricted in any way.

Certain centrifugal pumps, Hypro, for example, do not require pressure relief valves in the discharge circuits. These pumps are designed to allow certain slippage inside the volute (impeller housing) and pressure as well as volume can be safely controlled with a "throttling valve", usually a ball valve in the discharge line that either restricts the output flow or diverts part of that flow back to the tank. A hydraulic agitator (eductor) can safely be used in this system.

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But, if we rush through the job to get it done quicker so as to be able to get out of our Tyvek Coverall that is like a set of “Fat-Farm Monkey Suits”, we are only kidding ourselves.

A spray job done to quickly is not an effective job and therefore we may have to come back and do it again.

Let’s do things well the first time. And that means spraying at a rate where the coverage is effective.

Speed has a lot to do with how far the spray travels. One of the comparisons I usually use when I’m teaching application techniques is the one of the steam locomotive stopped in the depot. When the engine is stopped, the steam from the chimney goes straight up.

When the engine is running at 50 miles per hour, the steam is pushed down against the engine. Take that and turn it on its side, and you have your sprayer. The faster you move the boom, volute or hand wand, the less the spray is going to travel in the direction you are pointing it.

Another thing to remember is with air-blast sprayers: for the spray and the air to reach the target, the air in-between has to be displaced and pushed out of the way. Think of this and try to visualize and you will realize that the more you “dwell” in one place, the further the spray patterns go. (this is a favorite of the sprayer salesmen, they always demonstrate the blower in a standing position and, of course, the wind carrying the spray displaces the air and goes quite far – very impressive!).

Try running your air-blast sprayer at a slower ground speed and you will get more reach and coverage and that way be able to do the job right the first time, even though it takes longer.

This will also apply to boom sprayers, especially if you want to get good under-leaf coverage in heavy foliage situations.

When hand spraying, wands should be held steady…let the vortex created by the spinners behind the nozzles, do the “swirling” for you.

Remember: when you slow down, cut down the rate so that you do not saturate and dribble a lot of chemical on the ground.

Calculating Tractor Speed.

Very often, when out in the field and somebody asks me about tractor speeds, I’m at a loss. Tractors do not have speedometers and those that have the little chart of speeds to RPM’s and Gear Ratios pasted on the console, the chart, of course is all scratched up and mostly illegible.

The simple way to calculate speed is by remembering (or having a little card handy) on how long it takes to cover distances in one minute. So here goes, and try to remember it:

I don’t recommend spraying at speeds higher than 2 mph. Again, I feel that doing it once properly is better than having to go back and do it again.

Remember to cut down your dosages accordingly.

Most pesticides and other materials sprayed on crops are formulated to be as emulsifiable as possible, but many contain elements that either do not dissolve (wettable powders-WP), petroleum distillates (Emulsifiable Concentrates- EC) or just precipitate as they are heavier than the water (fertilizers, powdered metals, etc).

We will not get into the chemical compositions of the materials, but how to maintain them in suspension in the spray tank during the entire spray operation. Adjuvants play a major role in bonding the otherwise un-mixable spray materials with water, but there are some cases in which even the best adjuvant cannot keep these materials afloat.

We are growing evermore conscious of the need for effective tank agitation and most of the better sprayer manufacturers are constantly improving their designs to optimize the efficiency of their machines in that area. But the finest and most advanced agitation system in a sprayer will not assure a uniform application unless the operator does his job properly.

One of the most common causes of uneven application due to poor agitation lies with the spay applicator…

The habit of:

• Not agitating during Mixing/Loading
• Turning off the PTO drive that operates the sprayer pump and agitator during the drive to the field
• Turning off the PTO when reaching the end of a row or field
• Shutting down a sprayer with material in the tank when going on break or driving from field to field
• Restricting return agitation lines when the pump is wom, so as to be able to maintain pressure
• Not periodically inspecting the agitation systems (mechanical or hydraulic) to prevent failure, i.e. propeller wear, seal wear, nozzle wear, corrosion, etc
• All or any of the above by believing the adjuvants are enough to keep everything mixed.

Another of the most common causes of poor agitation is the actual design of the sprayer. In my years as a sprayer specialist I have come to appraise that probably 70% of the sprayers manufactured in the US have poor agitation systems, basically because of the lack of hands-on experience of the people that design and build them.

Most manufacturers pay attention to tanks, chassis/frames, pumps and delivery systems and put what they think is an agitator in the tank. Be it mechanical or hydraulic (return agitation) the fact that they are able to create turbulence in the water covers that subject for them…….. WRONG!!!

The foremost and basic requirement for effective tank agitation is for the movement of water (turbulence) to actually “sweep” the bottom of the tank so that any precipitated material is picked up and re-mixed with the rest of the solution. This is also important because most of the tanks discharge to the pump from the very bottom.

Some even have sumps to catch up to the last drops of material. So, if we have precipitation of material in the bottom of the tank, the pump is going to suck up a concentrate that could be many times what the label recommends or allows, with the subsequent problems:

• A – too much material in one area and not enough on the rest of the crop.
• B – concentrated chemical can cause permanent damage to crops.
• C – lack of control due to material being too diluted. A wasted effort.
• D – violation of Federal and State Law.

The key to effective agitation is to move the contents of the tank in one direction, such as a swirl. Many sprayer manufacturers make the mistake of orienting their hydraulic return nozzles in two or more directions in the tank.

This creates a total confusion of movement in the water and, although it looks effective, does not properly cover the critical area, which is the bottom of the tank. I know, because when I was designing and building sprayers, I was an advocate of this sort of agitation until, as a grower, I realized it did not do the job.

Mechanical agitation systems also have a drawback, especially in cylindrical tanks. Because of location of shafts and blades, the agitators cannot sweep the bottom of the tank and, although they do produce the “swirl” effect, there is always some material that precipitates and stays out of their reach.

The fact that they are considerably ineffective when the tank is in its last quarter is redeemed by the fact that any precipitation at that stage would not be as concentrated as when there is a full load of chemicals in the tank.

Mechanical agitators require attention. Replacement of seals (they are always leaking through the tank bulkhead fittings: a waste, also a no-no from a safety and environmental standpoint), blade breakage, belts, etc. Be sure you inspect them regularly.

Cylindrical and Oval tanks are the ideal configuration for the “sparger” type hydraulic return agitation system. This system consists of a tube located longitudinally along the wall of the tank, some 6 to 10 inches above the lower centerline, with volume booster nozzles aimed at that centerline so that they sweep across the bottom and produce a swirl with the axis of the tank as the center, this assures full agitation at all times (as long as it is operating!)

Irregularly shaped tanks (which tends to show us that the designers are thinking first of appearance and size, rather than functional operation) are the most difficult to assure effective agitation. There again, the bottom of the tank must be swept to keep concentrations of precipitants from getting to the pump and the crops.

The most effective agitators for these tanks are specifically placed and oriented volume boosters mainly aimed across the bottom, but away from the pump line inlet, so as not to create cavitation (injection of air) that could cause inefficiency and even damage to the pump.

Vertical cylindrical tanks are also difficult to properly agitate. Most manufacturers of sprayers with these tanks tend to install vertical nozzle agitators that create a “fountain” effect that does show up nicely on the surface when one looks down to see if the agitator is working, but fails miserably when it comes to mixing near the bottom.

Other sprayer designers have put horizontal agitators up to 1 foot above the bottom: this does not sweep. Others have them pointing in three directions, which causes a lot of turbulence but also fails to assure that the bottom will be clean.

Consequently, the key to good agitation is always the bottom of the tank. Look at it. If you have to modify it, you may want to do it yourself: extending pipes, changing orientation of nozzles, putting in spargers or volume boosters. All this can be done relatively simply with pvc pipe and fittings from your local plumbing supply.

If your tank has hydraulic return agitation, but does not have a volume booster nozzle, order one and install it. Volume booster nozzles take a small amount of water pumped into their venturi chamber and create a vacuum that draws 3 to 4 times the volume from the surrounding water and expels it out the end.

Consequently, with a return line generating 2 gpm you have a total output of 8gpm, and so forth. This means that you can have a healthy agitation volume without taking too much away from your pump system.

Look at agitation as stirring the sugar into your coffee. It is the same principle, except that, unlike sugar, many of the materials do not dissolve in the water and you have to keep stirring the spoon the entire time you have them in the tank.

It seems that the client’s building had palms in the atrium which were infested with mites. The population got so out of control that the cobwebs were everywhere and, despite intensive spraying with everything in his arsenal, the contractor could not control the mites.

The culprit: Hydrolisis

The solution: the building’s owner hired another interiorscape contractor that successfully controlled and eradicated the mite infestation.

The means: knowledge of hydrolisis, its effects on pesticides, and its prevention.

Hydrolisis is the breakdown of the active ingredients in carbamate and organophosphate pesticides caused by high alkalinity. In spray water, high alkalinity can be pH levels over 7.5 The breakdown progresses virtually geometrically as the pH levels go up. And, in the case of the palms in the atrium, the contractor was filling the sprayers in the bathrooms of the building using city water that had a pH of 8.5!

What this means is, that by the time the applicator filled the sprayer, mixed in the miticide and finally got out to the atrium, the high pH in the water had broken down the active ingredient in the miticide and the spray on the palms had the same effect as : Milk!

It was a hard lesson to learn and maybe one we should review periodically, as we all tend to overlook bits of information that could be instrumental to the success of our operations, in this case, spraying pesticides for their true effect: Killing Bugs!

Controlling Hydrolisis is very simple. It just means knowing the pH level of the water you are using to fill your tanks and correcting it to a reasonable acid level, between 6.0 and 6.5. This is a safe range where most pesticides will work well and maintain their potency.

Adjust the pH level in your water by adding acid. This can be phosphoric acid, vinegar, or some of the various "buffering" agents available as surfactants, emulsifiers, conditioners, spreaders, stickers and “snake oils” through your friendly chemical supplier. I personally prefer to use the acid and, in the case of small loads (backpack or hand pump sprayers) vinegar.

A general rule of thumb is that 6 oz of 80% Phos Acid will lower the pH from 7.2 to 6.5 in 100 gallons of water. However, mineral compositions of water vary with location, so your best bet is to test it yourself. A pool water tester will do the trick.

Several universities and professional groups have studied hydrolisis in pesticides and have published charts on individual pesticides and how they break down at various pH levels. I am not going to bore you with all this data, as during my trails and tribulations in the spray business, I have found that both your insecticides and fungicides will work well in the 6 to 6.5 range.

You may now notice some data on this subject in the newer labels, as the chemical companies are now becoming more responsible and publishing some of the information that previously they would keep to themselves. But don’t count on this across the board.

If you still need more specific information on particular products, ask your extension agent or chemical salesperson.

They are, of course, more modern and have many advantages over the traditional piston pumps, especially because the liquids being pumped never come into contact with the pump’s working parts. (In piston, plunger and roller pumps, the upper working parts are generally lubricated by the liquids being pumped, and the bearings and seals are always in contact with those chemicals).

However there is an aspect about diaphragm pumps that the user is generally not aware of, and certainly, in most cases, not mentioned by the manufacturers of the diaphragms in these pumps. Diaphragm pumps are designed to be pushed, not pulled. When they pressurize the liquids, they are being thrust by a piston and are properly seated on the head of the piston for that purpose. Thus, they are fully supported and therefore do not stretch, pull, deform or suffer any other stress that they were not designed for.

When the piston ends its stroke, it pulls the diaphragm as it goes back into the lower part of the cylinder, creating a slight vacuum in the pressure chamber that draws new liquid into the head, which will then be pushed out to the discharge hoses by the diaphragm. when it is pushed again by the piston.

As long as the inlet lines from the tank are not clogged, the filter is clean, and the shut-off valve in the line feeding the pump is open, there is no problem. The diaphragm pulling the liquid into the chamber is not stressed.

However, if there are obstructions in the line of any kind, the diaphragm has to pull hard to fill the chamber, creating what is called a high vacuum. This now causes the diaphragm to be pulled by the piston head, deforming the center mounting of the diaphragm.

If the pulling effect becomes extreme due to a higher degree of clogging, and, of course, a higher inlet vacuum, then the diaphragm will be severely deformed and even be scoured by the edge of the washer holding it to the head of the piston. Inevitably, the washer will cut the diaphragm, and you will have the subsequent mixing of oil and water. And that means diaphragm failure.

The best prevention for this problem:

• Keep filters clean
• Wash the screens out thoroughly after each application

Also, check your inlet flow periodically for blockage. Do this by disconnecting the inlet line from the pump and observing the flow. If the liquid (and please. do this with clean water so you don’t inadvertently dump chemicals) flow is normal, no problem. If you get a trickle or little more, and not what you would consider normal. Then you have got some blockage either in the line or plumbing.

Chemicals, especially wettable powders and coppers have a habit of cakeing-up in the fittings and sprayer lines. Also look for rags and other foreign objects as these also have a habit of ending up in drains and pipes. As a last resort: call your friendly RotoRooter man!

Another common cause of the high vacuum problem is shut-off valves in the inlet lines that are closed when the sprayer is started. Diaphragm pumps will pump air when there is no liquid around, so if your inlet line is closed, they will sit and suck vacuum with the subsequent consequences.

If you take simple precautions and periodically check and clean out your inlet lines, you will find that your diaphragms will last much longer than you expected and you will not only be satisfied with your pump’s performance, but save time and money as well.

If you are spraying intensively (every two weeks or so), make sure you replace the diaphragms and do a full maintenance job on your pump annually.