Spray application manual
31 January 2025
Module 11: Pumps, plumbing and components
11.15: Pressure gauges
Published 24 January 2025 | Last updated 20 January 2025
It is important to have two pressure gauges on each spray rig. One of the pressure gauges should be used to show the spray operator the pressure at the pump and the other used to show the pressure at the nozzle.
The gauge showing pressure at the nozzle can be a digital readout in the cab, with the sensor mounted as close to the nozzles as possible (e.g. reading directly from the boom line). If using a liquid pressure gauge, the gauge should be mounted outside of the cab, ideally near the windscreen. The ideal liquid pressure gauge would be at least 100mm (3.94”) in diameter, with the preferred operating pressure displayed at the top of the dial.
Calibration trialling rig pressure gauge
7 January 2025Calibration for trailing rig pressure gauges. Another video from GRDC's Spray Application GROWNOTES™ series.
Bill Gordon: It's very common on a lot of trailing rigs to have a pressure gauge located near the front of the machine, where they're reading pressure close to the manifold. The only problem with that is it's not really representative of the pressure that's going on in the line back on the spray rig. If you actually measure pressure in the spray line, you might find it's quite different to what you're reading here, particularly near the extremities of the boom.
So I try and look at a remote pressure sensor in the line near the back if you want to read accurate pressure or read pressure in the spray line itself. You can then remark this gauge up here to make sure it's reading accurately if you want to know what pressure is going on through the nozzle. This is really important for knowing what droplet size you're producing.
Outside windscreen pressure gauge
Tips
Large differences in pump pressure and nozzle pressure may indicate restrictions in the spray lines due to poor plumbing or blocked filter screens.
Plumb liquid pressure gauges into a T-piece, with a manual ball valve at one end, to allow the gauge to be primed and flushed.