For Best Results, Mix It Up

Getting the best product from spray equipment

By Andrew Greess

When it comes to spray equipment, mixing products well is critical. This is particularly true for landscape and golf applications that involve products that are not water-soluble, such as granular fertilizers.

A number of problems may occur if a product is not mixed well:

• Incorrect or uneven application rates. In either case, money will be wasted on buying the extra product, redoing the work, or fixing undesired results.

• Tank buildup. This occurs when materials settle at the bottom of the tank. If no action is taken, it can become severe and may require complete replacement.

• Clogged lines. This can clog downstream components, such as the filter. If the filter is not cleaned out, the pump may become starved for water and damaged. Hoses, fittings and spray tips also can become clogged, resulting in downtime and increased repair costs.

So how do you ensure good tanking mixing? There are several options

Mechanical Agitation

This is accomplished by turning a series of stainless-steel paddles attached to a stainless-steel shaft that runs through the tank. The shaft is turned by a pulley attached by a belt to the gas engine that also drives the pump. When the engine is on, the tank is agitated. Properly designed, mechanical agitation provides excellent, continuous agitation.

Considerations:

• It must be installed when the system is built; it is usually not feasible to add it retroactively.

• It is expensive because all the parts are precision-engineered stainless steel.

• Service eventually will be required as seals and bearings that allow the shaft to turn begin to leak.

• The sprayer will be out of service during the time the mechanical agitation is serviced.

Jet Agitation

A more common 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.

Considerations:

• There must be enough jet nozzles 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 are positioned toward the pickup tube that feeds the pump. The flow from the agitation nozzle can interfere with the pump intake.

• It is usually less costly than mechanical agitation. The primary cost of jet agitation occurs when 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.

• Calculations must be made 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:

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

2. Most agitation nozzles provide a multiplier (usually 3x, 5x or 7x), which reduces the flow of water required for agitation. Continuing the example above with 3x nozzles, the 24 GPM 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.

Mix Tanks

These 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 effective if you have multiple sprayers and a lot of material to apply. 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.

Considerations:

• A downside is the expense of a separate unit.

• A high-volume pump with readily available replacement parts should be selected.

• The output at the cone bottom of the tank should have an anti-vortex fitting; without it, a vortex--or whirlpool--effect may occur that prevents the adequate flow of material out the bottom of the tank.

• The pump and hoses should be plumbed with detachable cam fittings so that the pump can be used to fill, mix, and empty the tank.

Pre-Mix

If you have legacy equipment with insufficient agitation, the best option may be pre-mixing material in a bucket of water, then dumping it into the tank. If there is a spray hose and gun, the gun is used to spray water 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 potential issues before they become problems that require expensive repairs and significant downtime.

Andrew Greess is the President of Quality Equipment & Spray, which designs and builds custom landscape, golf- and pest-control spray equipment solutions.