How is thermal minimum flow calculated?

From energy balance at shut-off: Q_min,th = P_so / [ρ(Cp·ΔT_max + g·H_so)], with P_so ≈ 0.5·P_rated by default. Forms that divide head by η in the denominator under-predict thermal flow and are not used.

When does thermal flow exceed hydrodynamic MCSF?

High shut-off power, high head, low density / Cp, or a tight ΔT_max can push Q_min,th above the hydro band. The calculator then warns that the thermal bound governs.

How is ARC valve Cv estimated?

US liquid Cv = Q_gpm √(SG / ΔP_psi) at Q_MCSF. Pair with bypass NPS from Q / v_max on Sch 40. Confirm with the ARC vendor for flashing and control range.

Pump Minimum Continuous Stable Flow (MCSF) & Thermal Protection — Water 200 m³/h · H_so 150 m · 110 kW | FieldEngineersKit

Parameter	Value
Service fluid	Water

Engineering Reference & ASME Code Basis

1. Core Formula & Variable Definitions

API 610 / ISO 13709 — centrifugal pumps for petroleum, petrochemical, and natural gas industries · Hydraulic Institute HI 9.6.1 — NPSH margin and low-flow / MCSF guidance · Field practice: continuous min-flow / ARC for high-energy services

Q_MCSF = max(Q_min,th, Q_min,hydro)

Q_min,th = P_so / [ρ(C_p·ΔT_max + g·H_so)] · Q_min,hydro = Q_BEP·f_MCSF

API 610 / ISO 13709 · HI 9.6.1 MCSF · ARC / min-flow bypass screening

Code API 610Guide HI 9.6.1Thermal ΔT_maxBypass ARC Cv

Shut-off power defaults to 50% of rated driver power (typical API 610 centrifugal band 40–60%). Thermal minimum uses energy balance at H_so — do not divide H by η in the Q_min denominator. Hydrodynamic MCSF defaults to 35% of Q_BEP (adjust 30–60% per OEM / specific speed). High-energy pumps (>300 kW) need continuous ARC protection.

Q_BEP (Best efficiency flow) — Published BEP capacity from the OEM curve (m³/h or GPM).
H_so (Shut-off head) — Zero-flow head used for thermal energy balance (m or ft).
P_so (Shut-off shaft power) — ≈ so_ratio × P_rated (default so_ratio = 0.50).
Q_min,th (Thermal minimum flow) — P_so / [ρ(Cp·ΔT_max + g·H_so)] converted to m³/h or GPM.
Q_min,hydro (Hydrodynamic MCSF) — Q_BEP × mcsf_ratio (default 0.35; typical 0.30–0.60).
Cv (ARC bypass valve Cv) — US liquid Cv = Q_gpm √(SG / ΔP_psi) at Q_MCSF.

2. Allowances, Tolerances & Standards

This app screens thermal vs hydrodynamic bounds. The published OEM MCSF always governs final setpoints.

P_so / P_rated0.40–0.60 (default 0.50)

Typical shut-off power fraction for API 610 centrifugals.

Hydro MCSF ratio0.30–0.60 of Q_BEP

Ns- and OEM-dependent vibration / recirculation band.

ΔT_max default5 °C / 9 °F

Common thermal screening rise; tighten for flashing or seal limits.

High-energy alert> 300 kW (≈ 400 HP)

Continuous ARC / automatic recirculation is mandatory practice.

Quick Reference Lookup Table

Illustrative MCSF cases (this app)
Case	Focus	Units
Water 200 m³/h · H_so 150 m · 110 kW	Default API water duty	Metric
Boiler-feed 150 m³/h · H_so 300 m · 200 kW	Hot high-head thermal check	Metric
Naphtha 350 m³/h · H_so 180 m · 160 kW	Light HC / low Cp	Metric
Crude 1200 GPM · H_so 450 ft · 250 HP	Refinery crude	Imperial
Amine 800 GPM · H_so 650 ft · 300 HP	High-pressure API 610	Imperial

3. Material & Code Limitations

Rotodynamic (centrifugal) API 610 / ISO 13709 style pumps. Not for PD pumps or multiphase slurry without OEM data.

Material Group	Temperature Range	Allowable Stress / Limit	Engineering Notes
API 610 OH / BB / VS centrifugals	Fluid Cp / ρ at duty T	OEM MCSF on curve	Use published MCSF when available; this screen fills gaps in TA.
High-energy / boiler-feed	Hot water / flashing risk	>300 kW driver	Continuous ARC is expected — intermittent bypass is not enough.
Light hydrocarbons	Low Cp raises ΔT risk	Seal / flush limits	Thermal bound can approach hydro MCSF — recheck ΔT_max.

Code Applicability & Safety Boundaries

Field screening only — not an API 610 datasheet or HI acceptance test.
P_so ratio and MCSF% are engineering estimates until OEM values are entered.
ARC Cv is liquid ISA-style sizing — confirm choked / flashing with the valve vendor.
Export / PDF is a TA worksheet — not a stamped pump or bypass design.

4. Step-by-Step Worked Example

Field VerificationShow

Worked example — water 200 m³/h · 110 kW

Screen MCSF for an API 610 water pump at Q_BEP = 200 m³/h, H_so = 150 m, P_rated = 110 kW, ΔT_max = 5 °C, hydro ratio = 35%.

Fluid:Water · ρ 992 kg/m³ · Cp 4.18 kJ/kg·°CQ_BEP / H_so:200 m³/h · 150 mP_rated / so_ratio:110 kW · 50%ΔT_max / f_MCSF:5 °C · 35% of Q_BEP

Shut-off power

P_{so} = 0.50 \cdot P_{r a t e d}

P_so = 0.50 × 110 = 55 kW

Result:P_so = 55 kW

Thermal minimum flow

Q_{min, t h} = P_{so} / [ρ (C_{p} Δ T_{ma x} + g H_{so})]

With ρ=992, Cp=4.18 kJ/kg·K, ΔT=5 °C, H_so=150 m → Q_min,th ≈ 9 m³/h

Result:Q_min,th ≈ 9 m³/h

Hydrodynamic MCSF

Q_{min, h y d r o} = 0.35 \cdot Q_{B E P}

0.35 × 200 = 70 m³/h

Result:Q_min,hydro = 70 m³/h

Governing MCSF

Q_{M C S F} = max (Q_{min, t h}, Q_{min, h y d r o})

max(9, 70) = 70 m³/h

Result:Q_MCSF = 70 m³/h

Open /water-200m3h-hso-150m-p-110kw for the live default.

Conclusion: Hydrodynamic MCSF governs for this water duty. Size ARC / bypass for ≥ 70 m³/h and confirm the OEM published MCSF before locking trips or recycle setpoints.

5. Frequently Asked Questions & Technical References

Show

Minimum Continuous Stable Flow is the lowest continuous capacity allowed without unacceptable vibration, internal recirculation, or thermal rise (API 610 / HI 9.6.1). Always prefer the OEM published MCSF when available.