A center pivot waters a circle, but fields are rarely circular, so the corners of a square field would go dry if nothing extended the pivot's reach. The end gun is the big sprinkler at the outer tip of the pivot that throws water well beyond the last regular sprinkler to cover those corners, and end-gun control is the logic that turns it on and off at the right places around the circle. This guide explains how the end gun extends the wetted radius, how angle-based sequencing using mechanical cams or GPS decides when it fires, why it usually needs a booster pump, and how a modern control system automates end-gun arcs as part of a field's irrigation prescription.
Pivot End-Gun Control in one line: A pivot end gun is a large, long-throw sprinkler mounted at the outer end of a center pivot that extends the irrigated radius to reach field corners the regular sprinklers cannot cover. End-gun control turns the gun and its booster pump on and off based on the pivot's angular position, so it fires only over the arcs where extra reach is needed and shuts off where it would spray roads, buildings, or neighboring land. Sequencing is driven either by mechanical cams on the pivot's center or by GPS position, and a control system can automate multiple on and off arcs as part of an irrigation prescription.
A center pivot is a long span of pipe on wheeled towers that rotates around a fixed center point, laying down water in a circle as it sweeps. The regular sprinklers along the pipe wet the circle out to the radius of the last sprinkler, but a square or irregular field has corners and edges that fall outside that circle and would remain unirrigated. The end gun addresses this by mounting a powerful sprinkler at the very tip of the pivot that projects a jet of water far beyond the end of the pipe, temporarily extending the wetted radius outward to reach into those corners.
Because the end gun only helps where the field extends past the pivot's circle, running it all the way around would be wasteful and often harmful. Over the parts of the rotation where the field is bounded by the circle, or where the pivot's tip is near a road, a property line, a building, or a watercourse, the gun should be off; over the corners where the field extends beyond the circle, it should be on. End-gun operation is therefore inherently intermittent, keyed to where the pivot is pointing, and getting those on and off points right is the whole task of end-gun control.
The reach the gun adds is real but limited and weather-dependent. A long-throw gun can add a substantial band beyond the pipe, but its coverage is less uniform than the regular sprinklers and its jet is more affected by wind, so end-gun-watered corners typically receive a less even application than the body of the circle. That is an accepted trade-off, because the alternative is either leaving the corners dry or investing in a more complex corner-arm system. For most fields, an end gun sequenced correctly around the rotation is the practical way to pull the corners into production.
Since the gun must switch based on where the pivot is pointing, end-gun control is fundamentally about knowing the pivot's angular position and acting on it. The older, mechanical method uses a cam ring at the pivot's center point. Adjustable tabs or cams are set around a ring so that as the pivot rotates, a follower rides the ring and trips a switch that turns the end gun and its booster on when the pivot enters a corner arc and off when it leaves. Setting up cams is a physical job of positioning tabs to match the field's corners, and while it is robust and needs no electronics, it is coarse to adjust and limited in how many arcs and how much nuance it can handle.
The modern method uses GPS. A position sensor on the pivot reports its exact angle, and the control panel switches the end gun on and off at programmed bearing thresholds. GPS sequencing is far more flexible than cams: the operator enters the angles for each on and off transition into the controller, can define several separate arcs around the circle to match an oddly shaped field, and can change the arcs from a screen rather than by climbing to the center to move tabs. Because the position is known precisely and continuously, GPS also makes it straightforward to coordinate the gun with the pivot's speed and with other functions, and to keep the gun reliably off over sensitive areas.
Whichever method is used, the aim is the same: fire the end gun only over the arcs where the field needs it and keep it firmly off everywhere else. Precise sequencing is not just about efficiency; it is about not spraying water and, in the case of chemigation, chemical onto roads, ditches, buildings, or a neighbor's land. GPS control simply makes it easier to get those boundaries exactly right and to adjust them as needed, which is why it has increasingly replaced cams on modern machines.
An end gun needs more pressure than the regular sprinklers to throw its jet the extra distance, and the pivot mainline usually cannot spare that pressure at its far end. The solution is a booster pump mounted near the end of the pivot that raises pressure to the gun only when the gun is running. This is why end-gun control almost always switches two things together: the gun's valve and the booster pump. When the sequencing logic decides the gun should be on, it starts the booster and opens the gun; when the gun should be off, it stops the booster to save energy and avoid deadheading the pump against a closed gun. Coordinating the booster with the gun is part of what a proper end-gun control scheme handles.
In a modern system, the end gun's arcs are just one element of an overall irrigation prescription for the field. Variable-rate and GPS-guided pivot controllers let the operator program not only how fast the pivot travels and how much water each part of the circle receives, but also exactly where the end gun and booster fire, all as a coordinated plan tied to angular position. The controller executes that prescription automatically every rotation, extending reach into the corners while respecting every boundary, without an operator standing by to flip a switch. The end gun thereby becomes an automated, programmable feature of the pivot rather than a manual add-on.
Managing that across many pivots, often spread over large distances and running unattended, is where cloud SCADA adds value, bringing to agriculture the same remote supervision platforms like Merobix provide in oil and gas and other industries. A pivot's controller can report its angular position, whether the end gun and booster are currently running, and its pressure and status to a central dashboard, so an operator sees at a glance which machines are watering, whether the end gun is firing where it should, and whether a booster has failed to build pressure. Alerts flag a pivot that has stopped, an end gun that did not switch as scheduled, or a booster deadheading against a closed gun, letting a manager confirm that every field's prescription, corners included, is actually being executed without driving out to each machine.
A center pivot waters in a circle, but most fields are square or irregular, so the corners fall outside the circle the regular sprinklers can reach. The end gun is a large, long-throw sprinkler at the tip of the pivot that projects water well beyond the end of the pipe to pull those corners into the irrigated area. Without it, the corners of a square field would stay dry and unproductive.
End-gun switching is based on the pivot's angular position around its circle. The older method uses a cam ring at the center where adjustable tabs trip a switch as the pivot rotates into and out of a corner. The modern method uses GPS, where a position sensor reports the exact angle and the controller switches the gun on and off at programmed bearings, which is far more flexible and lets the operator define multiple arcs and change them from a screen.
The end gun must throw its jet much farther than the regular sprinklers, which requires more pressure than the pivot mainline can supply at its far end. A booster pump near the end of the pivot raises the pressure to the gun, and it is switched on and off together with the gun so it only runs when the gun is firing. This gives the gun the reach it needs while avoiding wasted energy and pump deadheading when the gun is off.
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