HOW IT WORKS:
Solution machines are designed to allow the application of dry soil amendments directly into irrigation water, as opposed to field spreading. Primarily Gypsum, but also potassium, limestone and various other fertilizers and soil amendments.
Accomplished through two primary functions:
 1) Vigorous agitation creates a uniform slurry inside the tank where the powder is mixed with a volume of water.
2) Meters the slurry into the irrigation water slowly to allow the mixture to go into solution and be carried out into the fields.

LOADING METHODS:
Three most common ways to fill the injection machine.
1) Hand loading using 50# bags.
Most common and simple.
- Labor intensive.
2) Fork Lift using 1-ton bags.
Much less labor intensive.
Saves $$ purchasing the amendments.
- Requires a fork lift at the pump site.
3) Bulk Silo.  (Bulk loading auger or Metered auger).
Virtually no labor required.
Saves $$ purchasing in bulk
- Costs more for equipment
- Not mobile.

AGITATION:
Because gypsum (and other amendments) are not truly water soluble, they require constant vigorous agitation to maintain the particles in suspension inside the main tank, prior to injection.

The vigorous agitation required and increased wear resulting from the thick slurry is why a common fertilizer injection system is not effective for gypsum injection.

POWER SOURCE:
Three primary sources of power:
1) Electric  (480v - 3 phase typical)
Most common, runs off of irrigation pump power source.
2) Gas  (Gas or Diesel)
Convenient for portability.
Allows use in remote areas with no electric power (pump from ditch).
3) Hydraulic   (Pump and Motor setup)
Convenient if a PTO is available. Requires no power or fuel.

PUMP:
Most all injection systems come with a positive displacement diaphragm pump, (Hypro D-30 or D-50), with an intake filter screen to catch large debris introduced into the main tank.
Simple to maintain with readily available parts.
Withstand abrasion much better than standard centrifugal pumps.
Will operate in virtually any type of irrigation system (high or low pressure).

CALIBRATION METHODS:
Two most common methods:
1) Pressure Relief Valve.
Original method. Adjusts slurry output by combining a particular p.s.i. pressure with a corresponding orifice disk. Excess slurry is routed back into the main tank.
2) Flow Meter.
Later designs use a flow meter to more accurately measure the gpm output of the injection system while also pre-diluting the slurry by adding fresh water prior to injection. This system is simpler, more accurate, more effective and requires less ongoing maintenance. It also allows for more gypsum to be added into the main tank, so refilling can be less frequent.

DECLINING RATE vs. BATCH:
Original injection machines were designed under the continuous process principal. This means that as the mixture in the main tank is pumped out, an equal amount of fresh water is let in, maintaining a constant fluid level inside the mixing tank.

The result of this continuous stream of incoming fresh water is the slurry is constantly becoming more and more diluted throughout the irrigation set. This causes the gypsum (or other amendment) to be injected on a "Declining Rate". More gypsum is injected early in the irrigation cycle when the slurry is thick. As the slurry thins, there is less gypsum being injected in each gallon of output from the machine.

While this is acceptable in many situations, controlled irrigation users are left with an uneven application of soil amendments. The obvious answer is to fill the machine with a predetermined batch of water and gypsum, and then simply turn off the flow of incoming water and allow the mixing tank to pump down throughout the irrigation. The slurry ratio remains virtually constant, while the level in the tank declines. This is known as "Batch Rate" application.

PLUMBING SETUP:
Plumbing in an injection machine is typically easy and virtually identical for any brand.
The injection system must have a source of fresh water, from either a ditch or pressurized water source.

And it must be located near the irrigation line so the solution pumped from the tank may be introduced into the stream of water. In closed systems such as drip or micro sprinklers, the injection machine should always be plumbed such that the output of the tank is injected at a point before any filtration systems. Shut off valves on both incoming and output hoses are usually installed for both safety and ease of maintenance.

MAINTENANCE:
Earlier equipment designs typically had a stainless steel shaft with mixing blades attached. The shaft extends lengthwise from one end of the machine to the other, positioned horizontally, near the bottom of the main mixing tank. The agitation shaft is supported by bearings at either end, along with a carrier bearing located in the middle of the mixing tank on some models. These models require more frequent maintenance as the entire shaft and bearings are below the water level and subject to accelerated wear and tear.

(Note: "Ag-Pro" brand injection machines with a horizontal shaft omitted the center carrier bearing and utilized patented end bearings that require far less maintenance than other horizontal-shaft design brands.)

Later designs incorporated a "Vertical" shaft design, with a single support bearing located above the water line and a vertical mixing shaft protruding down into the holding tank with a mixing blade at the end. This design is tends to require far less maintenance.

GYPSUM INJECTION EQUIPMENT

Currently, there are several manufacturers of injection systems designed specifically for injecting Solution Grade gypsum: (generally in the order of highest level of
features to lower priced):

Irrigation Solutions - (209) 668-4474 "Ag Solution Master" (Was Soils Solutions Corp.)

Soil Basics - (559) 651-2772 "Phertigator" Injection Machine

Agrigator - (661) 978-4787 "SDI" Injection Machine (& Silos)

American Ag - (661) 833-8311 "The Stinger" (Plastic Tank) Machine (& Silos)