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Banjo Flow Meter: Technical Description of Liquid Handling Systems in Agriculture
Quick Answer: A Banjo flow meter is a mechanical totalizer built for water and low-corrosion liquid fertilizers on spray rigs and irrigation lines. It measures volume locally with a typical accuracy of plus or minus 5 percent. For precise dosing of acids, viscous adjuvants, or remote monitoring with 4-20 mA HART, Silver Instruments supplies magnetic and oval gear meters that deliver 0.5 percent of reading accuracy.
Banjo meters use a plastic impeller inside a polypropylene housing. The impeller spins as liquid passes, driving a mechanical register through a magnetic coupling. Common sizes range from 1.5 inch to 4 inch, with models like the BFM series covering 5 to 100 US GPM. The display is a simple non-resettable totaliser. No external power is needed. The meter body threads directly onto camlock couplings or flanges, which makes field installation fast. In agriculture, you see these meters on nurse trucks, fertilizer injection carts, and water transfer lines where operators just need to know how many gallons went into a tank.
The simplicity has a cost. Banjo flow meters do not output an electrical signal. There is no 4-20 mA HART, no pulse, no Modbus. If your control room needs live flow data or batch records, you must read the mechanical numbers by eye. The accuracy drops when viscosity changes or when air bubbles pass through. The plastic impeller can seize if a liquid fertiliser like UAN crystallises inside the chamber. Farmers in Thailand and Vietnam have told us that fine sand in river water quickly wears the impeller bushings, making the reading unreliable. The polypropylene body is rated for pH 4 to 9; aggressive acids, solvents, and some surfactants cause swelling or cracking.
Here is the thing. When you graduate from simple batch recording to automated dosing or chemical injection, Silver Automation Instruments supplies alternatives that fit the same line sizes. For conductive liquids such as liquid NPK blends, potassium chloride brine, and diluted phosphoric acid down to 5 µS/cm, a Silver electromagnetic flow meter is a direct upgrade. It comes in DN15 to DN200, with PTFE or hard rubber liners and 316L or Hastelloy electrodes. Output options include 4-20 mA HART, pulse, and RS485. Galvanic isolation and IP67 enclosure are standard. Accuracy is 0.5 percent of rate. A paperless recorder can log flow totals and alarms for audit trails. For viscous fluids like crop oil concentrates or molasses-based biostimulants, our oval gear meter in 316 stainless steel handles 30 to 500 cP with optional PT100 temperature compensation. We have installed ten Silver elec
In practice, most farm managers skip the plastic meter once they need a 4-20 mA signal. A sugar cane cooperative in the Philippines used Silver low-cost electromagnetic meters to dose molasses into irrigation water, cutting waste by 12 percent in the first season. The meter paid for itself in three months.
To get a specific recommendation, send us your desired flow range (US GPM or m3/h), pipe size (DN), liquid name, and temperature. Email [email protected] or call Tel: +86-25-68650347. Our engineers reply within one business day.
Frequently Asked Questions
Can a Banjo flow meter handle 30 percent hydrochloric acid? No. The polypropylene body and plastic impeller degrade rapidly. For hydrochloric acid or other corrosive chemicals, Silver recommends a magnetic flow meter with a PTFE liner and tantalum electrodes. Send the concentration and temperature to [email protected] and we will confirm wetted material compatibility.
What is the accuracy difference between a Banjo meter and a Silver oval gear meter? A Banjo meter gives plus or minus 5 percent of full scale under ideal conditions. A Silver oval gear meter delivers 0.5 percent of reading across the stated viscosity range. For metering adjuvants that cost USD 20 per litre, the saving pays for the meter very fast.
How can I get a 4-20 mA signal from an existing Banjo installation? You cannot retrofit a mechanical Banjo meter with an analog output; the design has no electrical sensing. The simplest path is to replace it with a Silver electromagnetic flow meter. Provide your pipe diameter and flow range, and we will ship a calibrated meter with 4-20 mA HART ready to connect to your PLC or RTU.
What is the minimum conductivity for an electromagnetic meter on liquid fertilizers? Silver electromagnetic meters need at least 5 µS/cm. Most mixed liquid fertilizers, even diluted UAN, easily exceed this. If you are injecting a very low-conductivity oil-based additive, talk to us about an oval gear meter instead. Call or WhatsApp +86-25-52155837 for quick guidance.
How do I request a quote for a Silver flow meter to replace a Banjo unit on my spray rig? Email [email protected] with your current Banjo model, the liquid you spray, pipe size, and the flow range you typically run. We will cross-reference a meter that matches your couplings and gives the output your monitoring system needs. You can also reach us on WeChat at +86 15365082610.