Accurate chemical dosing is where quality, safety, and cost control meet. If your metering pump underdoses, processes drift and compliance slips. If it overdoses, you burn cash and risk downstream issues. The good news: you can validate real-world dose accuracy with simple tools – a calibration column and a stopwatch – and lock in repeatable results by placing the injection quill correctly.
Why Field Verification Beats Nameplate Numbers
Stroke length and speed settings tell you what the pump intends to deliver. Process conditions decide what you actually get. Gas in the suction, sticky checks, soft tubing, or pulsation can turn a setpoint into something very different. A quick calibration column test grounds your dosing in facts, not assumptions.
The Calibration Column Test (15 Minutes, One Tech)
What you need
- A clear, graduated calibration column installed on the suction side (between tank and pump)
- A stopwatch or phone timer
- The system at steady pressure and temperature
- Personal protective equipment for the chemical handled
Step-by-step
- Stabilize the system. Let the pump run at the normal stroke and speed for a few minutes. Purge any visible air from the suction line.
- Isolate the suction from the bulk tank. Close the suction valve from the tank. Open the valve from the calibration column to the pump. The pump should now draw only from the column.
- Set a start level. Fill the column above a clear graduation mark. Record the exact start volume.
- Time the drawdown. Start the stopwatch as the meniscus passes your start mark. Stop it at a convenient lower mark. Record the end volume and elapsed time.
- Return to normal. Reopen the bulk tank suction valve. Close the column valve. Do not leave the pump starved.
- Do the math.
- Volume drawn (ml) = start volume − end volume
- Elapsed time (min) = stopwatch reading
- Actual flow (L/h) = (volume drawn in ml ÷ 1,000) ÷ (time in minutes ÷ 60)
Example
- Start 1,000 ml, end 600 ml → 400 ml drawn
- Time 6 minutes
- Actual flow = (0.400 L) ÷ (0.1 h) = 4.0 L/h
Compare and correct
- If actual flow is within ±5% of target, you are in good shape
- If it is off, adjust the stroke first for coarse changes, then speed for fine trimming
- Repeat the test once to confirm stability
Pro tips
- Run the test at two or three operating points (low, normal, high) to map performance
- If the flow wanders between repeats, suspect air ingress on suction, leaking checks, or insufficient back pressure
Get Mixing Right: Injection Quill Placement and Tip Design
Even a perfect dose rate fails if the chemical dribbles on a pipe wall and never blends. The injection point is where accuracy meets mixing.
Where to place it
- Centerline of the host pipe. Use an injection quill long enough to reach the pipe center, not the sidewall. Centerline placement puts the chemical in the highest velocity zone, which improves mixing and reduces wall attack.
- Downstream of a turbulent element. A control valve, elbow, or static mixer downstream accelerates blending. Avoid dead legs and stagnant tees.
- Orientation matters. In horizontal lines, quill from the top into the center; in vertical lines, inject into downward flow when possible to avoid buoyant chemicals rising back.
Why the tip matters
- Spring-loaded check tip. Prevents backflow and siphoning, keeps the line primed, and reduces air ingress. Choose materials compatible with the chemical.
- Multiport or diffusing tip. For small lines or sensitive processes, a diffuser breaks the jet into smaller streams, improving near-field mixing.
A Quick Acceptance Checklist After Adjustments
- The calibration column shows a dose within ±5% at the normal setpoint
- Repeatability within ±3% over two runs
- Steady discharge pressure (minimal gauge flicker)
- The injection point is centerline, leak-free, with a functioning check tip
- No foaming or spitting at sampling points downstream (indicates good mixing)
If you want help selecting calibration columns, quills, and the right back-pressure and dampening setup for your line, our team can review your system and provide a simple, high-confidence configuration. Call Vissers Sales Corp. at 1-800-367-4180 or visit our industrial pump accessories page to get started.
Let’s make every dose count.