Eliminate Crushed Floats: Magnetic Level Indicator Maintenance & Best Practices

Magnetic level indicators (MLIs) are among the most reliable level measurement devices in industrial service — but they're not immune to damage. One of the most preventable failures is a crushed float, which occurs when operators don't follow proper commissioning and startup procedures. Here's how to prevent this costly mistake and extend your MLI service life.

The Problem: How Floats Get Crushed

Real-World Case: Sugar Mill

A sugar mill in Central America learned this lesson the hard way. During their annual equipment restart, they brought a magnetic level indicator back online at their operating pressure of 1,300 PSI (90 bar). The startup went wrong because of a simple sequencing mistake: the operator opened the lower isolation valve first and opened it too quickly.

What happened next: A liquid slug entered the level chamber at full system pressure — 1,300 PSI of force instantly applied to the float. The float, designed to move freely at normal operating conditions, couldn't withstand that pressure differential. Result: crushed float, damaged indicator, and unplanned downtime.

This wasn't a design flaw. It was a procedural failure — and it's entirely preventable.

Why Float Damage Happens

Magnetic level indicators work by a simple principle: a float moves up and down inside a chamber as liquid level changes. External magnetic indicators track the float's position. The float itself is typically aluminum or similar lightweight material — perfect for normal operation but vulnerable to sudden pressure shocks.

Three Common Failure Modes:

1. Rapid Valve Opening (Most Common)

• Opening isolation valves too quickly on startup

• Creates pressure differential across the float

• Float gets pinned and crushed

• Result: permanent indicator failure

2. Pressure Surge During Operation

• System upset or unexpected pressure spike

• Float can't escape the surge

• Similar crushing damage occurs

• Less common but catastrophic

3. Improper Blowdown Procedure

• Opening drain valve improperly

• Allows system pressure to push into chamber

• Float damage if float is in wrong position

• Preventable with proper sequencing

Best Practice: Proper Commissioning Sequence

This is the procedure every operator should follow:

Step 1: Open Upper Isolation Valve First The upper valve connects the level chamber to the steam or gas space above the liquid in your vessel. Opening this first allows pressure to equalize from above. Do this slowly — don't rush it.

Why it matters: This equalizes pressure in the upper part of the chamber before you introduce liquid pressure from below.

Step 2: Wait for Pressure Equalization Give the system 30-60 seconds for upper pressure to stabilize. Watch the indicator — it should start showing a reading as pressure equalizes.

Step 3: SLOWLY Open Lower Isolation Valve After upper valve is open and equalized, very slowly open the lower isolation valve. Open it gradually over 1-2 minutes if possible. This allows liquid to enter the chamber gradually without shocking the float.

Why it matters: Slow entry means the float experiences gradual pressure differential instead of sudden shock. The float has time to move naturally.

Step 4: Verify Normal Operation Once both valves are fully open and the system is at normal operating pressure, check that your magnetic indicator is reading correctly. The float should move freely in response to level changes.

Step 5: Document Initial Reading Record your initial level reading for baseline comparison during operation.

Magnetic Level Indicators vs. Glass Gauges

This is one advantage MLIs have over direct-reading glass gauges:

Feature	MLI	Glass Gauge
Commissioning Risk	Low (if done right)	Very low (solid glass)
Float Damage Risk	Moderate (operator error)	None (no moving parts)
Visibility in Dark Areas	Excellent (magnetic response)	Requires lighting
Durability at 1,000+ PSI	Excellent	Good
Maintenance Frequency	Low	Higher (blowdown, cleaning)

Both designs are valuable — MLIs excel at visibility and automation; glass gauges excel at reliability in extreme conditions.

Prevention Checklist

Before you restart any magnetic level indicator system:

☐ Review commissioning procedure with operators

☐ Mark isolation valves with open/close sequence

☐ Confirm upper valve opens first

☐ Commit to slow opening (60+ seconds per valve)

☐ Verify float moves smoothly through full range

☐ Record baseline level reading

☐ Post startup procedures near the gage

Learn More

Jerguson magnetic level indicators are designed to last 20+ years with proper maintenance. Our technical support team is available to review your commissioning procedures and help prevent avoidable failures.