Dosing Line Too Small for a Flow Meter? GF 2000, 2507 and 2100 Small-Bore Solutions
A common frustration in dosing systems: you want to fit a flow meter at the metering pump discharge to verify how much chemical is actually being injected, only to find nothing will fit — because insertion paddlewheel sensors such as the 515 and 2536 require a minimum pipe size of 0.5 inch, while dosing branches are frequently DN10 or smaller. What is needed here is not an insertion sensor but an in-line small-flow sensor.
1. Why insertion sensors do not work on small bore
An insertion sensor relies on a paddlewheel protruding into the pipe to sense velocity, which requires enough bore for the wheel to be immersed in a stable flow profile. On small pipe the wheel will not fit, and the sensor body itself would obstruct most of the flow area, rendering the measurement meaningless. Small bore therefore demands a different principle: pass the entire flow through a calibrated full-bore chamber. That is the in-line approach.
2. The three GF small-bore models
| Model | Principle | Flow range | Line size | Body / rotor | Accuracy | Temperature / pressure |
|---|---|---|---|---|---|---|
| 2000 | In-line rotor | 0.11–12.11 L/min | 1/4″ tubing | PPS / PEEK | — | 0 to 80 °C, 80 psi |
| 2507 | In-line rotor | 0.4–12.0 L/min | 1/4″ tubing | PVDF / PVDF | ±2.0% of reading, repeatability ±0.25% of full range | −30 to 120 °C, 80 psi |
| 2100 | In-line turbine | 0.38–38.0 L/min | 1/4″, 3/8″, 1/2″ tubing and 1/2″ pipe | PVDF / PVDF | ±3% of reading, repeatability ±0.5% of reading | −20 to 70 °C, 130 psi |
All three run on 5–24 VDC with open-collector output and connect to a GF Signet transmitter or a PLC frequency input. Data from the GF official product range document.
3. Choosing between them for dosing duty
2507 — the first choice for aggressive chemicals
Both body and rotor are PVDF, with a temperature span of −30 to 120 °C, making it the most chemically and thermally capable of the three. It is the natural choice for sodium hypochlorite, acids and alkalis. Its ±0.25% of full range repeatability is also the best of the three, which matters where dose consistency is checked repeatedly.
2100 — the widest range
At 0.38–38 L/min its upper limit is more than triple the other two, and beyond 1/4″, 3/8″ and 1/2″ tubing it also fits 1/2″ pipe. Choose it where dose rates vary widely, or where one instrument must cover several injection points. The full-bore turbine design also keeps pressure loss low.
2000 — the lowest starting point
Its 0.11 L/min lower limit is the smallest flow any of the three will read, making it the option for trace injection of concentrated chemicals. The PPS body and PEEK rotor suit non-aggressive media within 0 to 80 °C.
4. The real value: an online health check for the metering pump
A metering pump's nameplate flow is a theoretical figure. Actual delivered volume is affected by back pressure, cavitation, diaphragm fatigue and crystallisation on the check valves — none of which is visible from outside the pump. Fitting a small-bore flow meter at the discharge turns "how much we think we dosed" into "how much we actually dosed".
Three typical uses: calibration, verifying the stroke-to-flow relationship on commissioning or after a diaphragm change; trend monitoring, where a gradual fall in flow at constant stroke usually indicates check valve crystallisation or diaphragm ageing, allowing maintenance to be scheduled before failure; and interlock alarms, raising an alarm or stopping the pump below a threshold to catch the most dangerous failure mode of all — a pump that is running but delivering nothing.
5. Installation notes
- In-line sensors are fitted into the line and must follow the marked flow direction; reversed, they produce no signal.
- Metering pump discharge is strongly pulsating. Install downstream of a pulsation dampener, otherwise the reading will swing wildly.
- Crystals or particles in the medium will jam both rotor and turbine types — fit a Y-strainer upstream.
- Size so that the normal operating flow sits in the middle of the range; readings close to either limit carry noticeably larger error.
For selection against your specific chemical, flow rate and line size, see our measurement and control instrumentation page or contact us.