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Metering Pump Specification: Mineral Injection System

Reference: RO-SPEC-001 §3.8, §5.5 — Water System Spec (Two-Tank Architecture)

Overview​

Three identical diaphragm metering pumps inject mineral concentrates into the water stream between solenoid valve SV-TREAT and Tank 2 (T-102). They operate only when SV-TREAT is open (T-102 calling for fill). Dosing rates are set by the active HMI recipe preset and are ratio-based relative to the transfer flow measured at FT-103.

Pump TagMineral ConcentrateRole in Coffee Water Profile
Mineral AMagnesium sulfate (MgSO₄)Extraction enhancer; brightness and clarity
Mineral BCalcium chloride (CaCl₂)Body and mouthfeel; total hardness
Mineral CSodium bicarbonate (NaHCO₃)Buffer capacity / alkalinity; balance and sweetness

Conductivity sensor CT-103 (located at T-102 inlet, after the injection point) provides closed-loop TDS verification against the active recipe target.

1. Core Performance & Compliance​

  • Quantity: 3 pumps (identical hardware; interchangeable spares)

  • Certification [CRITICAL] [VERIFY: photo of data plate]

    • Must meet NSF/ANSI 61 (Drinking Water System Components)
    • Must feature visible NSF-61 mark on the unit's data plate

  • Flow Rate Range [CRITICAL]

    • 0.1–100 mL/min adjustable (per water-system-spec §3.8)
    • Practical duty range during normal recipes: 1–15 mL/min (see §6 Dosing Duty Point Analysis)
    • Note: Many pumps are rated in GPH on the nameplate. 1 GPH ≈ 63 mL/min. Convert before comparing.

  • Turndown Ratio

    • Must support stable, precise dosing below 5 mL/min
    • Preferred: ≥ 1000:1 turndown (Grundfos DDA achieves 3000:1)

  • Pressure Rating

    • Minimum 50 PSI (3.4 bar)
    • Must overcome back-pressure in the line between SV-TREAT and T-102

  • Accuracy / Repeatability

    • ≤ ±2 % of setpoint (preferred ±1 %)

  • Adjustment Type

    • Digital stepper-motor drive (preferred) or digitally-controlled solenoid drive with equivalent precision
    • Onboard digital display showing dosing rate
    • Resolution: 0.1 % increments OR 0.1 L/h increments

2. Wetted Materials (Sanitary Grade)​

All materials in the liquid path must be NSF/ANSI 61 certified for potable water contact.

  • Dosing Head / Body

    • Acceptable: PVC, Polypropylene (PP), PVDF, or 316SS
    • PVDF or 316SS preferred for long-term chemical compatibility

  • Gaskets / O-Rings / Valve Seats

    • FKM (Viton) OR EPDM
    • PTFE gaskets acceptable

  • Valve Balls

    • Ceramic (preferred) or 316SS

  • Diaphragm

    • PTFE (Teflon) faced — mandatory for chemical resistance

  • Chemical Compatibility

    • Must support continuous dosing of the following at concentrate strength:
      • Magnesium Sulfate (MgSO₄) — mildly corrosive in solution
      • Calcium Chloride (CaCl₂) — corrosive to metals; avoid brass/copper
      • Sodium Bicarbonate (NaHCO₃) — mildly alkaline
    • Concentrate preparation follows the "A Waste of Coffee" method (see §6): ~35–75 g dry mineral per 800 mL distilled water. These are dilute solutions; material compatibility is not demanding.

3. Electrical & Control Interface​

  • Power

    • 100–240 VAC, 50–60 Hz (universal input)
    • Standard US 3-prong plug (NEMA 5-15P) or hardwired to panel
    • Typical power draw: 20–30 W per pump

  • Control Interface

    • "AR" variant (Analog + Relay) or equivalent
    • Must support: external stop via dry-contact relay (PLC-controlled)
    • 4–20 mA analog input for proportional dosing rate control (optional but preferred for future closed-loop TDS trim)

  • PLC Integration

    • Relay module: AutomationDirect P2-08TRS (Form-C relay output)
    • PLC enables/disables each pump independently via relay dry contact
    • Pump runs at its onboard setpoint when relay is closed; stops when open
    • Dosing rate is set manually on the pump's own display per the active HMI recipe; future upgrade path is 4–20 mA proportional control from PLC

  • Fittings

    • 1/4″ OD tubing, standard compression fittings (suction and discharge)
    • 316SS or PVDF injection quill at the discharge point

  • Enclosure Rating

    • IP65 / NEMA 4X minimum (wet environment near tanks)

4. Constraints & Preferences​

  • Pump Type [CRITICAL]

    • Diaphragm metering pump required
    • No peristaltic pumps (tube wear and inconsistent dosing at low rates)

  • Drive Type

    • Stepper-motor drive (e.g., Grundfos DDA) preferred for precision at low flow rates and long diaphragm life
    • Controlled solenoid drive (e.g., ProMinent gamma/X, Walchem EWN) is acceptable if turndown and precision meet §1 requirements

  • Price Range

    • $300–$1,200 per pump (new)
    • Used / surplus / open-box units acceptable if NSF-61 certification can be verified on the data plate and wetted parts are in serviceable condition

  • Preferred Manufacturers

    • Grundfos (DDA series)
    • ProMinent (gamma/X series)
    • Walchem / Iwaki (EWN series)
    • LMI / Milton Roy (PD series)

5. Qualified Models​

The following models meet all §1–§4 requirements. Any of these can be used; all three pumps should be the same model for spare-parts commonality.

Tier 1 — Best Match (stepper motor, highest precision)​

Grundfos DDA 7.5-16 AR (preferred)

ParameterValue
Type key (PVDF/PTFE)DDA 7.5-16 AR-PV/T/C-F-31U2U2FG
Type key (316SS/PTFE)DDA 7.5-16 AR-SS/T/SS-F-31VVBG
Max flow7.5 L/h (125 mL/min) @ 16 bar (232 psi)
Turndown3000:1
DriveVariable-speed stepper motor
Accuracy±1 %
DiaphragmPTFE
Power24 W, 100–240 VAC, 50/60 Hz
EnclosureIP65 / NEMA 4X
CertificationsNSF/ANSI 61, CSA-US, CE
ControlAR = Analog (4–20 mA) + Relay (dry contact stop)
Approx. price (new)$800–$1,200

Notes: The DDA is the only preferred-manufacturer pump with a true stepper motor drive. The 3000:1 turndown and ±1 % accuracy make it the best choice for precise low-rate mineral dosing. Available with Grundfos 2-week quick-ship through authorized distributors.

Tier 2 — Strong Alternatives (solenoid drive, good precision)​

ProMinent gamma/X GMXa 1604 (PP or PVDF head)

ParameterValue
Max flow3.6 L/h (60 mL/min) @ 232 psi
Stroke volume0.30 mL/stroke × up to 200 strokes/min
DriveControlled solenoid
Stroke adjustmentElectronic, 0–100 % continuous
DiaphragmPTFE-faced (vPTFE option available)
CertificationsNSF/ANSI 61 approved liquid ends
Approx. price (new)$500–$900

Notes: The gamma/X has predictive intelligence (sensor-free pressure measurement, fault detection). Widely deployed in municipal water treatment; commonly found on surplus markets. The GMXa 1009 variant (9 L/h, 145 psi) is also acceptable if 1604 is unavailable.

Walchem EWN-B11 or EWN-B16 (PVC head, PTFE/EPDM diaphragm)

ParameterValue
Max flow (B11)0.6 GPH (38 mL/min) @ 150 psi
Max flow (B16)1.0 GPH (63 mL/min) @ 105 psi
DriveSolenoid, up to 360 SPM
ControlR variant = manual + analog; Y variant = full-featured
DiaphragmPTFE + EPDM (dry end)
CertificationsNSF/ANSI 61, WQA, UL, CSA
Approx. price (new)$300–$600

Notes: Good budget option. High stroke rate (360 SPM) provides fine resolution. Available with PVC, PVDF, or 316SS heads. The EWN-Y controller adds flow measurement capability when paired with the EFS sensor.

LMI / Milton Roy PD Series (PD7xx)

ParameterValue
Max flowVaries by liquid end code; up to ~3 GPH (190 mL/min)
Turndown200:1
Accuracy±3 %
DriveSolenoid
DiaphragmLiquifram™ (PTFE)
CertificationsNSF/ANSI 61
Power110–240 V, 50–60 Hz
EnclosureIP65 / NEMA 4X
Approx. price (new)$300–$700

Notes: Widely available and economical. The ±3 % accuracy is adequate for this application because CT-103 provides closed-loop TDS verification. Less precise than Grundfos DDA but significantly cheaper. Common on surplus markets due to large installed base in municipal water treatment.

6. Dosing Duty Point Analysis​

This section calculates the actual metering pump duty range for the system's operating conditions, to help evaluate whether a given pump model is suitable.

Transfer Flow Rate​

When SV-TREAT opens, P-102 directs flow from T-101 through the UV unit and into the mineral injection manifold en route to T-102. The transfer flow rate depends on P-102's VFD speed setting during fill mode.

ScenarioTransfer FlowNotes
P-102 at full speed~4 GPMSV-RECIRC closes, full flow to SV-TREAT
P-102 at reduced speed~2 GPMPLC may throttle during T-102 fill
Minimum practical~1 GPMConservative low-end for duty calc

Recipe Dosing Rates (from water-system-spec §5.5)​

PresetMin. A (MgSO₄)Min. B (CaCl₂)Min. C (NaHCO₃)Target TDS
SCA Gold Cup2.4 mL/gal3.1 mL/gal1.8 mL/gal~120 ppm
Light Roast3.6 mL/gal1.5 mL/gal2.0 mL/gal~100 ppm
Medium Roast2.0 mL/gal2.5 mL/gal2.2 mL/gal~130 ppm
Rao/Perger3.0 mL/gal0.0 mL/gal1.5 mL/gal~85 ppm

Calculated Pump Output Range​

Pump output (mL/min) = Recipe rate (mL/gal) × Transfer flow (GPM)

ConditionDosing RatePump Output
Maximum: Light Roast MgSO₄ @ 4 GPM3.6 mL/gal × 414.4 mL/min
Typical: SCA Gold Cup CaCl₂ @ 2 GPM3.1 mL/gal × 26.2 mL/min
Minimum: Rao/Perger NaHCO₃ @ 1 GPM1.5 mL/gal × 11.5 mL/min
Zero: Rao/Perger CaCl₂ (any flow)0.0 mL/gal0 (pump off)

Practical duty envelope: 1.5–15 mL/min

All qualified models in §5 cover this range with margin. The Grundfos DDA (minimum output ~0.04 mL/min) provides the widest range for experimentation with extreme recipes.

Concentrate Preparation Reference​

Dosing rates above assume concentrates prepared per the "A Waste of Coffee" method (Alex Levitt), where 1 mL of concentrate added to 1 gallon of RO permeate raises TDS by 10 ppm (expressed as CaCO₃):

ConcentrateDry MineralDissolve In
Magnesium sulfate (MgSO₄·7H₂O)74.6 g800 mL distilled water
Calcium chloride (CaCl₂, anhydrous)33.6 g800 mL distilled water
Sodium bicarbonate (NaHCO₃)50.9 g800 mL distilled water

These are the gallon-scale concentrates. The recipe mL/gal rates in the HMI presets are calibrated to these concentrate strengths. If different concentrate strengths are used, the HMI recipe rates must be recalibrated during commissioning.

7. Sourcing Strategy & Search Keywords​

New Purchase (authorized distributors)​

  • Grundfos DDA: burtprocess.com, grundfos.com product selector, local Grundfos distributor — 2-week quick-ship available
  • ProMinent gamma/X: prominent.us, pulseinstruments.net — contact local rep for pricing
  • Walchem EWN: walchem.com, instrumart.com, cannonwater.com
  • LMI PD: procompumps.com, lmipumpcatalog.com

Used / Surplus (eBay, surplus dealers)​

Search combinations of:

  • "NSF 61" metering pump diaphragm
  • Grundfos DDA 7.5-16
  • Grundfos DDA dosing pump
  • ProMinent gamma X or ProMinent GMXa
  • Walchem EWN metering pump
  • LMI PD series pump or LMI PD7
  • "digital dosing pump" NSF diaphragm

Filter for:

  • Used / refurbished / open-box / industrial surplus
  • Listings with data plate photos (verify NSF-61 mark)
  • Listings with spec sheets
  • Confirm 100–240 VAC universal voltage (avoid 24 VDC-only variants)
  • Confirm tubing size (1/4″ OD standard)

What to Verify on Any Used Pump​

  1. NSF/ANSI 61 mark visible on data plate
  2. Voltage: 100–240 VAC, 50/60 Hz
  3. Diaphragm condition (replace if unknown history — kits are ~$50–$100)
  4. Check valve ball and seat condition
  5. Confirm correct liquid end material (avoid brass or exotic alloys)
  6. Confirm control interface supports dry-contact relay stop