alright so this has been bugging me for a while and im not sure if its a calibration thing or something hardware related. running an Agras T40, about 80 hours on it, and ive started noticing the flow rate drifting mid-mission. like i'll set it up for 1.2 L per minute across the boom and it starts fine but by the time im halfway through a tank it feels like its pushing more than that based on how fast im emptying. checked the nozzles, theyre not clogged, ran the pump calibration twice through the DJI app.

what i cant figure out is if its the flow sensor being flaky or if temperature is affecting the pump output. its been hot here, pushing 95-100F on the ground during most of these runs. talked to one guy locally who said he had a similar thing and it turned out to be the diaphragm pump just getting tired but i dunno, 80 hours doesnt seem like that much.

anybody dealt with this on the T40 specifically or even the T30 since the plumbing is pretty similar? i have a job this weekend and im trying to figure out if i need to pull the pump before then or if theres a software fix im missing

the flow sensor on these is a known weak point, not gonna sugarcoat it. had mine start giving garbage readings around the 60 hour mark, the readings in the app looked plausible enough that i didnt catch it for a couple missions and ended up over-applying on part of a corn field. not a disaster but not great either. if you can borrow a flow meter and just inline test it against what the aircraft is reporting youll know pretty quick if the sensor is lying to you.

also worth checking your connectors on the sensor harness, heat cycles loosen things up and ive seen intermittent connections cause exactly the kind of drift you're describing. that would be the free fix before you go pulling the pump apart

95-100F ambient is definitely within spec technically but if your chemical tank is sitting in direct sun the viscosity of whatever youre spraying can shift enough to matter depending on the formulation. probably not your whole problem but worth thinking about if youre doing fungicide mixes with anything oily. we started using insulated tank covers this summer and it helped consistency a bit, probably more placebo than anything but hey.

also have you tried doing the pump calibration with a fresh cold tank vs mid-day? curious if the baseline numbers look different