---
title: Pump Switching Stability
created: 2026-04-07
updated: 2026-04-07
status: proven
tags: [machineGroupControl, stability, switching]
sources: [nodes/machineGroupControl/test/integration/ncog-distribution.integration.test.js]
---

# Pump Switching Stability

## Concern
Frequent pump on/off cycling causes mechanical wear, water hammer, and process disturbance.

## Test Method
Sweep demand from 5% to 95% in 2% steps, count combination changes. Repeat in reverse to check for hysteresis.

## Results — Mixed Station (2x H05K + 1x C5)

Rising 5→95%: **1 switch** at 27% (H05K-1+C5 → all 3)
Falling 95→5%: **1 switch** at 25% (all 3 → H05K-1+C5)

Same transition zone, no hysteresis.

## Results — Equal Station (3x H05K)

Rising 5→95%: **2 switches**
- 19%: 1 pump → 2 pumps
- 37%: 2 pumps → 3 pumps

Clean monotonic transitions, no flickering.

## Why It's Stable
The marginal-cost refinement only adjusts flow distribution WITHIN a combination — it never changes which pumps are selected. Combination selection is driven by total power comparison, which changes smoothly with demand.