Pump and Spray Performance

Thursday July 19, 2012


Mr Pest Control


How can I measure output pressure (p.s.i.) at the nozzle of my JD-9 gun or lawn wand on my truck mounted spray rig? Not just the pressure the device is rated for. I am trying to evaluate major changes to the output p.s.i. of my spray rig and their ultimate effect... this may be plumbing changes, orifice configurations, aging components, and other variables that all have effects on the ultimate pressure of the insecticide applied. I am a pest control technician who utilizes this rig at least 5 days per week for perimeter spraying, lawns & outdoor commercial.

Richard, TX

Mr Pest Control


The ideal and most accurate way to measure pressure at the nozzle would be to have a pressure gauge installed on the spray gun, and JD-9 gunjets do come as one model tooled to accept a pressure gauge. If yours is not set up to screw a gauge directly onto the gunjet the next best thing would be to install a gauge in-line between the hose and the gunjet, and these are available as well. The gauge will probably feel like it is getting in the way if you leave it in place for all your work, but you could at least determine what the pressure is and then remove the gauge for your daily routines. 

Exactly what the pressure is at the nozzle tip where the liquid comes out varies, as you indicate, with a number of considerations. The diameter and length of the hose are big ones, and there is a dramatic drop due to friction between the pump and the end of the hose. You can find formulas for determining what this loss of psi is, but it still could be somewhat subjective and only an estimate. The kind of spray gun and the size of the orifice are also major considerations, and the larger the orifice the less resistance you have pushing back on the flow of the liquid, so a larger orifice should equate to somewhat lower psi actually coming out the nozzle. A "flood" or "shower" style nozzle reduces that even more and is probably the best kind of nozzle to use for turf applications, as you get a faster treatment of the turf with far less fine particles being produced, thus less drift. These kinds of lawn guns are available from Univar. The shower style nozzle would not be appropriate for spraying taller trees, so for that a JD-9 gunjet is good but with a fairly large orifice to put out the volume with less mist and fine droplets that drift. 

But, to get the most accurate reading of the psi at the tip of the gunjet you would want a gauge installed as close to that tip as possible. Knowing exactly what your output psi is could be a very important consideration, as many product labels may restrict what psi you are using for your application. Certainly this is a restriction on termiticide applications where guessing at the psi could be a problem. 

Mr. Pest Control

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Please note, Mr. Pest Control is answering questions supplied by PMP customers across North America. His answers are generated from industry and manufacturer-provided information. The answer may not be specific to the laws and regulations for your State, Province, Territory or Country. In addition, products mentioned may not be registered and or available in all areas. Always check with your local Univar office for specific information to your area. Always read and follow label directions.