Michael Turner
Choose a 15–20 L wearable tank with a piston or diaphragm pump rated at 30–40 psi (2–2.8 bar), fitted with 1.2–1.5 mm nozzles for general liquid treatments; select a 12 V, 8–10 Ah battery pack to achieve roughly 3–6 hours of continuous operation at medium pressure. Expect filled mass near 18–25 kg; prioritize a harness that transfers 50–60% of load to the hips and includes an adjustable sternum strap and ventilated padding.
Calibrate before each use: mark a 10 m × 10 m (100 m²) test area, walk at your normal working speed (target 3–4 km/h), spray across the plot for a fixed time or pass count, collect output in a graduated container and compute application rate as (liters collected × 10 000) ÷ 100 = L/ha. Typical target volumes: 100–300 L/ha for foliar coverage; for spot treatment measure per-plant dose (commonly 0.1–0.5 L per plant depending on species).
Nozzle selection and droplet size matter: for systemic herbicides choose coarse droplets 300–500 µm to limit off-target drift; for contact fungicides or wettable powders use medium-fine 150–300 µm to improve coverage. Verify nozzle flow at set pressure and replace any tip with >10% deviation from stamped output.
PPE and handling: wear chemical-resistant gloves, splash goggles and a respirator rated for particulates and vapors when mixing concentrates; keep a spill kit and access to water. Rinse the tank immediately after use with three successive fills, pumping each rinse through the wand to clear lines; dispose of rinse water according to local regulations.
Maintenance and storage: clean and inspect filters, O-rings and diaphragms monthly; lubricate seals per manufacturer’s schedule and replace worn hoses. Drain the vessel for winter storage and keep electrical components dry. For rechargeable packs, recharge after each day of work and avoid long-term storage fully discharged; follow cell-type recommendations for state-of-charge during off-season storage.
Selecting pump type and nozzle size for a field applicator
Use a chemical-resistant diaphragm pump rated 40–60 psi (2.8–4.1 bar) with a flow of 1.5–3.0 L/min for general foliar applications in a knapsack-style applicator; choose a piston pump (60–120 psi / 4.1–8.3 bar, 3–6 L/min) only when high-pressure, narrow-jet tasks are required. Constructive materials: PVDF or polypropylene housings with Viton or EPDM seals for glyphosate and common pesticide mixes; stainless internals for corrosive liquids.
Nozzle selection: prefer flat-fan tips for uniform broadcast deposits, hollow-cone for fine droplet coverage on tall vegetation, and coarse solid-cone orifice nozzles for thicker stems or soil incorporation. Match nozzle flow to pump output and intended application rate (L/ha) to avoid overpressure or starvation; keep working pressure inside the pump’s rated band to preserve diaphragm life.
| Pump type | Pressure (psi / bar) | Flow (L/min) | Best for | Notes |
|---|---|---|---|---|
| Diaphragm (chemical-resistant) | 40–60 / 2.8–4.1 | 1.5–3.0 | Broadcast foliar, most pesticides and fertilizers | Good chemical compatibility, modest weight, low maintenance |
| Piston | 60–120 / 4.1–8.3 | 3–6 | High-pressure spot work, long-reach nozzles | Higher wear, heavier, higher flow capability |
| Centrifugal | 10–30 / 0.7–2.1 | 4–8 | High-volume rinsing, non-chemical tasks | Poor for fine atomization, limited chemical resistance |
| Nozzle type | Typical codes/orifice | Droplet category | Application rates (L/ha) | Working pressure (psi / bar) |
|---|---|---|---|---|
| Flat-fan | 11002–11004 | Medium to coarse | 100–400 | 30–40 / 2.1–2.8 |
| Hollow-cone | 8001–8003 | Fine to medium | 50–250 | 30–50 / 2.1–3.4 |
| Solid-cone / high-flow | 3.0–5.0 mm orifice | Coarse | 300–800 | 20–40 / 1.4–2.8 |
| Turbo/air-induction | AI11003–AI11005 | Medium-large, reduced drift | 100–400 | 30–40 / 2.1–2.8 |
Practical checks: measure actual nozzle output at the pump pressure (collect for 30 seconds) and calculate L/ha for target speed; verify pump current draw against battery capacity if using a powered unit–see battery sizing guidance at best cordless lawn mower with battery and charger. Replace diaphragms every 1,000–1,500 operating hours under chemical use, and carry a spare nozzle set matched to the most common application rates you perform.
Calculating tank capacity and expected application duration per fill
Recommendation: size the reservoir to supply the required output plus 20–30% reserve; use Required tank (L) = Q (L/min) × T (min) × 1.25 where Q is nozzle output and T is desired continuous run time.
Continuous run calculation: Runtime (min) = V (L) ÷ Q (L/min). Example: a 12 L vessel with a nozzle output of 0.6 L/min yields 12 ÷ 0.6 = 20 minutes continuous operation.
Intermittent operation (triggered or pulsed use): use duty fraction D (0–1). Expected duration (min) = V ÷ (Q × D). Example: same 12 L, Q = 0.6 L/min, D = 0.40 → 12 ÷ (0.6 × 0.40) = 50 minutes usable time.
Usable volume and minimum reserve: reserve 5–10% to prevent air ingestion and to allow mixing/agitation. Usable V = Total V × (1 − reserve). For a 15 L container with 8% reserve, usable = 15 × 0.92 = 13.8 L.
Chemical dilution and total finished solution: when using concentrates, compute finished volume: Finished V = concentrate V × (1 + dilution ratio) (for 1:99, finished = concentrate × 100). Determine how many fills of finished mixture you need by dividing required finished volume by usable V.
Area coverage per fill: if application rate is R L/ha, then Area per fill (ha) = Usable V (L) ÷ R (L/ha). Example: usable 13.8 L, rate 200 L/ha → 13.8 ÷ 200 = 0.069 ha (690 m²).
Unit conversion quick reference: 1 US gallon = 3.785 L; 1 imperial gallon = 4.546 L. Convert volumes before plugging into formulas.
Practical sizing guidance: for spot treatments use 2–5 L usable; for routine maintenance tasks choose 8–12 L usable; for prolonged site work consider 15–20 L usable. Increase capacity when dilution schemes produce low finished-solution concentration or when area per fill must be maximized.
Mixing ratios and safe handling of treatment chemicals in the carried applicator
Mix at the label-specified concentration; common examples: 0.1% w/v = 1 g per L (≈3.8 g/US gal), 0.5% v/v = 5 mL per L (≈19 mL/US gal), 1% v/v = 10 mL per L (≈38 mL/US gal), 2% v/v = 20 mL per L (≈76 mL/US gal).
- Standard mixing sequence for a portable tank unit:
- Fill the tank about 25–33% with clean water.
- Add water‑dispersible powders as a slurry (pre‑mix in a separate bucket at 1:3 powder:water if dusty).
- Pour flowables/solutions next; maintain gentle agitation.
- Add emulsifiable concentrates after solids are wetted.
- Add adjuvants and surfactants last, unless the product label specifies otherwise.
- Top up to final volume and maintain agitation during use.
- Measuring and accuracy:
- Use a dedicated, chemical‑resistant graduated cylinder or calibrated pump for liquids; tolerance ±1–2% for concentrated actives.
- Use an accurate balance (0.1 g resolution) for powders; record batch weights.
- For small doses (<5 mL) use syringes or pipettes designed for chemical resistance.
- Worked calibration example:
- Label: 2% v/v product in final mix. Tank capacity: 12 L. Required product = 0.02 × 12 L = 0.24 L = 240 mL.
- If target application rate is 10 g a.i./ha and carrier volume is 100 L/ha → concentration = 10 g / 100 L = 0.1 g/L.
Personal protection and handling
- PPE minimum: chemical‑resistant gloves (nitrile ≥0.4 mm or butyl for solvents), goggles or face shield (EN166), long‑sleeve chemical‑resistant coverall, chemical boots. Add a respirator with organic vapor cartridges and P100/HEPA filters for solvent‑based or high‑drift aerosols.
- Mix outdoors or in a well‑ventilated, non‑windy area; use a splash shield when pouring concentrates.
- Never use hands or household utensils to measure actives; keep dedicated tools clearly marked and stored separately from food/preparation items.
- Avoid cross‑contamination: dedicate a set of tools for oxidizers and another for organics; rinse and air‑dry tools after each use.
- Skin contact response: immediately remove contaminated clothing and rinse affected skin with running water for 15 minutes; seek medical help if irritation persists.
- Eye exposure: flush with water for 15–20 minutes and obtain urgent medical attention.
- Ingestion: do not induce vomiting unless instructed by poison control or medical personnel; bring the chemical label to responders.
Cleaning, rinsing and storage
- Empty container handling: triple‑rinse with clean water, add rinsate to the tank for use where label permits, and puncture containers before disposal per local rules.
- Tank and line cleaning: flush with clean water, then use a detergent wash; for products that leave residues follow label neutralizer instructions. Keep cleaning water out of storm drains and collect rinsate for authorized disposal.
- Storage: keep chemicals in original labeled containers, locked, ventilated, and between 0–30°C. Store incompatible materials separately (e.g., strong oxidizers apart from organics and amines).
- Spill response: have an absorbent spill kit, gloves, goggles and a containment tray. Contain liquid, absorb, collect in labeled hazardous waste container and notify authorities if release reaches surface water.
- Recordkeeping: log batch mixes, product lot numbers, volume prepared, operator name and date for traceability and regulatory compliance.
Daily inspection: seals, hoses and leak-prevention steps before operation
Pressurize the unit to 25 psi and hold for 2 minutes; visibly inspect every joint and seam for liquid seepage or soap bubbles before beginning work.
Quick checklist (3–7 minutes)
O-rings and gaskets: inspect all O-rings for cracks, flattened cross-section >0.5 mm, surface glazing or hardening; replace any showing damage. Typical replacement interval: every 100 operating hours or once per season. Use identical material (Viton for solvents/oils, EPDM for water/acidic mixes).
Hoses: look for soft spots under finger pressure, bulges, exposed reinforcement braid, abrasion, kinks. Minimum recommended working-rating: 200 psi for common portable applicators; inner diameter commonly 1/4″ or 3/8″ – match original spec. Replace hoses older than 2 years or with any defect.
Fittings and clamps: prefer stainless-steel worm-drive or ear (Oetiker) clamps. Clamp seating should deform hose slightly without cutting the cover. Replace split or corroded clamps immediately.
Step-by-step leak-test and corrective actions
1) Fill with clean water to operating level; run internal pump for 10–15 seconds to purge air. 2) Pressurize to working pressure (25–30 psi typical); monitor gauge for 5 minutes – acceptable drop: ≤3 psi. 3) Apply a soap solution (1 part dish soap : 10 parts water) to all joints and fittings; observe for bubbles for 60–120 seconds. 4) If bubbles appear: depressurize, remove clamp, cut 5–10 mm off hose end, inspect barb for burrs, re-seat hose at least 10 mm past barb shoulder, install new clamp and retest.
Sealing lubricant: use a thin film of silicone grease on elastomer seals; do not use petroleum-based lubricants on EPDM. For solvent-compatible systems specify Viton-compatible grease.
Chemical-residue control: after using any active agent flush tank and lines with two full tank-volumes of clean water, then run neutralizer rinse if product label requires. Close and store dry; do not leave residues sitting in hoses overnight.
Perform checks in shade or under cover to avoid heat-driven expansion during testing – consider a best lawn chair with umbrella or a best large golf umbrella for a comfortable inspection area.
Storage and handling: always depressurize and drain before storing, coil hoses without sharp bends, keep unit out of direct sunlight and below 40°C, and log replacements (date, hours) for seals and hoses to maintain a predictable change schedule.
On-site refilling protocols, source testing and contamination prevention
Refill only from potable municipal supplies with turbidity <1.0 NTU and free chlorine ≥0.20 mg/L; reject any source outside those limits until corrective action (filtration or disinfection) is completed and verified.
For private wells or surface sources perform a full test before every fill: turbidity (NTU), pH (6.5–8.5), and presence/absence coliform test on a 100 mL sample. If coliform present or turbidity >1.0 NTU, install a 1 µm cartridge filter and apply a disinfection step (target free chlorine 0.5 mg/L with 30 min contact) before using water to fill the portable applicator.
Use a dedicated refill hose fitted with an in-line one-way valve and vacuum breaker; maintain a visible air gap ≥25 mm between hose outlet and source surface during transfer. Color-code hoses (e.g., green for potable, red for chemical) and mark each hose with last-cleaned date. Do not submerge hose ends into open reservoirs or buckets.
After emptying any chemical tank perform triple-rinse: fill with ~10% of tank capacity for each rinse (agitate 30 seconds), fully drain, repeat three times. Example: 20 L unit → three rinses of 2 L each. Capture all rinseate in a labeled containment drum for analysis or disposal per label/local regulation; do not release rinseate to drains or stormwater.
Secondary containment for the refill area: portable bund or tray sized to at least 110% of the largest unit being filled. Position bund under fill point and keep a spill kit on hand sized to absorb the entire fill volume (minimum 10 kg universal absorbent for single-unit operations). Train staff on spill procedure and inspect kits monthly.
PPE for refilling and testing: nitrile gloves (≥0.4 mm), chemical splash goggles meeting ANSI Z87.1, chemical-resistant apron, and a half‑face respirator with cartridges rated for the product class when vapors are possible. Keep an ANSI-compliant eyewash station within 10 m of the refill location.
Field test equipment and thresholds: portable turbidity meter (0.1–1000 NTU), DPD chlorine test kit (0–5 mg/L), pH meter or strips (6.5–8.5), and coliform presence/absence kits (24–48 h). Calibrate meters weekly and log calibration date and operator initials.
Record-keeping: log date/time, unit ID, source type, test results (turbidity, free chlorine, pH, coliform), operator initials, hose ID, and corrective actions. Retain logs for 36 months and attach any laboratory confirmations for bacteriological results or chemical residues.
Cross-contamination controls: dedicate one set of hoses and fittings for potable fills and another for chemical handling; flush and triple-rinse any shared fittings and visually inspect seals before reuse. Neutralize residuals per product label–example neutralizers: 1–2% sodium bicarbonate rinse for acidic residues and 0.5–1% citric acid rinse for alkaline residues–then verify final rinse pH 6.5–8.5 before returning to service.
Testing cadence: municipal source – spot-check free chlorine and turbidity weekly and after any supply interruption; private source – full pre-fill test each time, weekly bacteriology if filling multiple units per week. If any test fails, tag affected units “DO NOT USE” and quarantine until corrective measures and re-test confirm compliance.
