Power Sprayer Agitation - For Best Results, Mix it Up!

When it comes to power spray equipment, ensuring your product is well mixed is critical. This is particularly true for landscape and golf applications that involve products that are not water soluble, that is, they don’t stay dissolved in water. Granular fertilizers are a good example of this type of product.

• Incorrect application rates. If the product is not well mixed in the weed sprayer tank, you could be applying the product at the incorrect rate or applying the product unevenly. In either case, you will not achieve your desired results and you will be wasting money on extra product, redoing work or fixing undesired results.

• Tank Build Up. If the material is not well mixed, it will settle to the bottom of the power sprayer tank. If no action is taken, the tank buildup can become severe. We have seen instances where the material coagulates on the bottom of the tank into a solid mass. If not dealt with, eventually the material will build up to the point where the tank must be replaced.

• Clogged Lines. If the material is not properly mixed, it can be sucked into lines and clog downstream components. The first part to be clogged will be the filter. If your staff is checking the filter frequently, they should be able to identify the problem, which will allow you to take action and prevent equipment damage.

If the filter is not cleaned out, the pump could become starved for water. This can result in pump damage and if the pump is continued to run dry, it can become a total loss. The material can also clog hoses, fittings and spray tips, which can cause system damage, resulting in downtime and increased equipment repair costs. We have seen a number of instances where plumbing fittings have been completely clogged and the pump totally destroyed.

Now that we have discussed the issues that can result from insufficiently mixed product, we will talk about how to ensure good tank mixing.

A.     Mechanical Agitation

Mechanical agitation is a very effective way to ensure a good tank mix. Mechanical agitation is accomplished by turning a series of stainless steel paddles inside the tank. The paddles are attached to a stainless steel shaft that runs through the tank. The shaft is turned by a pulley that is attached by a belt to the gas engine that also drives the pump. When the engine is on, the tank is being agitated. Properly designed, mechanical agitation provides excellent, continuous agitation.

The downside is that mechanical agitation must be installed when the system is built, it is usually not feasible to add it retroactively. Mechanical agitation is also expensive because all the parts are precision engineered stainless steel. Eventually the seals and bearings that allow the shaft to turn will leak and require service. The sprayer will be out of service during the time the mechanical agitation is serviced.

B.     Jet Agitation

Jet agitation is a more commonly used solution because of its lower cost. Jet agitation involves splitting off a portion of the pump’s output back into the tank through carefully positioned jet agitation nozzles.

A couple of important considerations for jet agitation. The there must be enough jet nozzles in the tank to stir up the entire tank and the nozzles must be positioned so there are no dead spots in the tank that are not agitated. It is also important to make sure that none of the agitation nozzles is positioned toward the pickup tube that feeds the pump. The flow from the agitation nozzle can interfere with the pump intake.

Usually jet agitation is less costly to install then mechanical agitation. The primary cost of jet agitation is that sometimes a larger pump is required that has sufficient output (measured in gallons per minute) to drive the agitation in addition to the spray hose or spray boom.

It is important to do the appropriate calculation to ensure the system has the appropriately sized pump. If the pump is too small, performance will be unacceptable. Here are some quick rules of thumb.

Liquid products require 8% of tank volume (in gallons per minute) for jet agitation. Dry or granular products require 12% of tank volume. For example, if planning to use a granular fertilizer in a 200 gallon tank, you will require 24 gallons per minute (12% times 200 gallons) for agitation.

Most agitation nozzles provide a multiplier (usually 3X, 5X or 7X) which increases the effect of the agitation. Said another way, the agitation nozzles reduce the flow of water required for agitation.

Using the example above with 3X nozzles, the 24 GPM requirement is reduced to 8 GPM (24 GPM divided by 3).  

The number of nozzles does not affect the calculation. For this example, a pump is required that puts out at least 8 gpm MORE than is required to drive the boom or spray gun. If the pump output is insufficient to drive the output and the agitation, you will not be able to operate agitation at the same time you are spraying. 

Check out Hypro 3X Agitation Jets 3371

Check out Hypro 5X Agitation Jets 3371-0028

C.  Mix Tanks

Mix tanks are separate cone-bottom tanks with dedicated high volume pumps that mix products into water which is then pumped into spray units. These units are great if you have multiple sprayers and a lot of material to apply. The downside is that the expense of a separate unit is incurred. Mix tanks usually rely on high-volume centrifugal pumps to churn the material in the tank, which is then drawn out the bottom of the tank and pumped into individual sprayers. The pumps can be gas or electric powered.

Some considerations when selecting mix tanks.   

Select a high volume pump for which replacement parts are readily available. Be sure the output at the cone bottom of the tank has an anti-vortex fitting. Without this fitting, a vortex or whirlpool effect may form that prevents the adequate flow of material out the bottom of the tank. Be sure that the pump and hoses are plumbed with detachable cam fittings so that the pump can be used to fill the tank, mix the tank and empty the tank.

D.    Pre-Mix

If you have legacy equipment with insufficient agitation, your best bet may be to premix your material in a bucket of water, then dump it into the tank. If there is a spray hose and gun, use the gun to spray back into the tank to help mix the material.

To ensure great results, review your spray equipment to ensure products are being properly mixed and applied. Be sure employees are trained to mix products and to look for and identify issues before they become problems requiring expensive repairs and significant downtime.