Westlock Limit Switch — Crystallizer Drop Valve

Point at Each Part to Learn

// Hover or tap parts on the diagram to see details

⚙️ The Cam: #1 Problem Child

The cam is mounted on the valve stem. As the stem rotates, the cam physically pushes the microswitch lever inside the Westlock housing.

Common Cam Failures

Slipped: Came loose, rotated off position
Worn: Grooved from friction over time
Broken: Sheared off completely
Misaligned: Installed wrong at factory

✅ How to Check It

Manually move valve stem
Watch cam contact switch
Should click clearly at both positions
Mark correct position with paint pen

Live Valve Cycle

// or drag the slider manually

CLOSED 0% — CLOSED OPEN

🔒CLOSED

⚠️MOVING

🔓OPEN

Position

OFF

Cam Contact

0 VDC

Signal Out

CLOSED

DCS Reads

// What's Happening Right Now

Valve is CLOSED. Disc is sealed against seat. Cam is NOT contacting the switch lever. Switch contacts are OPEN. DCS sees 0 VDC — reads "Closed".

Wiring Lab

Terminal Reference

COM

Common

Always has 24VDC power.
Connect to + supply.

Normally Open

Closes when valve opens.
→ PLC input (open confirmation).

Normally Closed

Opens when valve opens.
Used for alarms / closed confirmation.

Field Test Procedure

Test 1: Power Check

Set multimeter to VDC
Black probe to ground
Red probe to COM terminal
Should read: 24VDC ±10%

Test 2: Continuity

De-energize circuit (LOTO)
Set meter to continuity (beep)
Probe COM and NO terminals
Manually move valve
Should beep when open

Click a Scenario to Diagnose

🔴🔓

DCS shows CLOSED but valve is visibly OPEN

▶

Diagnosis: Cam slipped or broken — not triggering the switch

1
Inspect cam position on stem
2
Check if cam physically hits switch lever during stroke
3
Re-adjust cam alignment on stem
4
Mark correct position with paint pen

⚠️🔒

Switch won't change state — stuck in one position

▶

Diagnosis: Dead switch or no power to COM terminal

1
Check 24VDC at COM terminal
2
Test switch continuity manually (de-energize first)
3
Inspect wiring at junction box for looseness/corrosion
4
Replace switch if continuity fails both ways

⚡📊

Signal flickers on/off randomly

▶

Diagnosis: Loose wiring or vibration causing intermittent contact

1
Tighten all terminal screws
2
Inspect wire insulation for cracks or chafing
3
Check conduit for damage
4
Add vibration dampener on conduit if needed

🔄❌

Valve moving but no signal change at all

▶

Diagnosis: Cam not making contact with switch lever — gap too wide

1
Watch cam during valve stroke (visually confirm gap)
2
Measure gap between cam and switch roller
3
Adjust switch mounting position or cam position
4
Verify cam isn't worn down to nub

Diagnostic Decision Tree

START: Switch showing wrong position │ ├─ Is valve actually moving? │ │ │ ├─ NO → Check actuator / air supply first │ │ │ └─ YES │ │ │ ├─ Does cam physically touch switch lever? │ │ │ │ │ ├─ NO → Adjust cam position ✅ │ │ │ │ │ └─ YES │ │ │ │ │ ├─ Continuity test PASS? │ │ │ │ │ │ │ ├─ NO → Replace switch ✅ │ │ │ │ │ │ │ └─ YES → Check wiring to PLC ✅

// Pro Tips

📸 DOCUMENT WHEN WORKING

Take photos of correct cam position before you touch anything. Saves future-you 2 hours of head-scratching.

🎨 PAINT PEN IS YOUR FRIEND

Mark alignment on stem and cam. Visual reference beats memory every time.

🔊 LISTEN FOR THE CLICK

A healthy microswitch clicks audibly when cammed. No click = dead switch or misaligned cam.

⚡ TEST UNDER LOAD

Switch might work dry but fail with 24VDC applied. Always test energized (safely, following arc flash program).