Quartz 4

SSO Flow Switch

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Flow Switch - Quick Reference SSO

Device Type: Binary Input - Flow Detection
Signal: Dry contact (NO or NC)
Power: Unpowered (mechanical switch) or 24VAC (relay type)
Version: 1.0 | Date: Dec 2025

DEVICE OVERVIEW

Common Models:

  • McDonnell Miller FS4-3/FS7, Cleveland Controls AFS, Dwyer WFS/SFS, Gems FS-200, Johnson Controls F61/F63

Used For:
Proof of water flow (chilled water, hot water, condenser water), pump status verification, freeze protection, low flow alarm, interlock safety

Technologies:

  • Paddle Type: Mechanical paddle in pipe flow, contact closes when flow pushes paddle
  • Thermal Dispersion: Heater element, flow cools element, triggers switch
  • Target (Vane) Type: Spring-loaded target, flow overcomes spring, closes contact
  • Differential Pressure: Measures ΔP across orifice, switch triggers at setpoint

Specifications:

  • Pipe Sizes: 1/2” to 12” (varies by model)
  • Flow Range: 0.3-10 ft/sec typical (consult manufacturer)
  • Setpoint: Adjustable (gpm or ft/sec)
  • Contact Type: SPDT typical (NO, NC, COM)
  • Contact Rating: 1-5A at 24-250VAC
  • Connection: NPT threaded (1/2”, 3/4”, 1”) or flange mount
  • Material: Brass, stainless steel, or plastic (application dependent)

Environment: Varies by liquid type (water, glycol, oil)

SAFETY - PPE REQUIRED

  • ☑ Safety glasses (ANSI Z87.1)
  • ☑ Heat-resistant gloves (pipes may be hot or cold)
  • ☑ Face shield (if system under pressure)
  • ☑ Chemical-resistant gloves (if glycol or chemicals)

HAZARDS

  • ⚠️ PRESSURIZED SYSTEM - Water systems under 30-150 PSI
  • ⚠️ HOT WATER - Up to 200°F in heating systems
  • ⚠️ COLD WATER - 35-45°F in chilled water (cold burns from prolonged contact)
  • ⚠️ CHEMICAL EXPOSURE - Glycol, water treatment chemicals (if leak)
  • ⚠️ WATER DAMAGE - Improper installation causes leaks

SYSTEM ISOLATION REQUIRED

  • MANDATORY: Close isolation valves upstream and downstream
  • Drain system pressure in section being worked
  • Verify 0 PSI with pressure gauge before opening pipe
  • Keep bucket/absorbent ready for residual water

COORDINATION

  • Notify building operator of system shutdown
  • Coordinate with mechanical contractor or plumber
  • Plan work during off-hours if possible (minimizes impact)
  • Verify bypass valves available (if equipped)

INSTALLATION CHECKLIST

TOOLS NEEDED

  • Pipe wrenches (two - for installation and backup)
  • Teflon tape or pipe dope
  • Drill + bits (for paddle insertion hole)
  • Hacksaw or tubing cutter (if modifying pipe)
  • Wire strippers (18AWG)
  • Multimeter
  • Bucket and rags (for water drainage)
  • Pressure gauge (verify 0 PSI)
  • Label maker

MATERIALS

  • Flow switch (correct pipe size and flow range)
  • Pipe fittings (if needed: Tee, nipples, unions)
  • Teflon tape or pipe thread sealant
  • Isolation valves (if not present)
  • Wire (18AWG)
  • Wire nuts or terminal blocks
  • Ball valve or drain (for testing)

PRE-INSTALL

  • Verify flow switch rated for:
    • Pipe size (must match)
    • Flow range (gpm expected)
    • Liquid type (water, glycol, oil)
    • Temperature range
    • Pressure rating
  • Identify installation location:
    • Straight pipe section (10× pipe diameter from elbows/valves)
    • Accessible for service
    • After pump (in flow direction)
  • Verify isolation valves present or plan to install

INSTALL STEPS - PADDLE TYPE (Most Common)

STEP 1: System Isolation

  1. Notify building operator
  2. Close isolation valves upstream and downstream
  3. Open drain valve to depressurize section
  4. Verify 0 PSI with pressure gauge
  5. Place bucket under work area

STEP 2: Prepare Pipe

OPTION A: Existing Tee/Boss (Preferred)

  • Use existing threaded opening in pipe
  • Clean threads and apply Teflon tape

OPTION B: Install New Tee (Requires Pipe Modification)

  1. Cut pipe at selected location
  2. Install Tee fitting with unions for future service
  3. Ensure Tee points in flow direction (arrow on switch)
  4. Pressure test before proceeding

OPTION C: Hot Tap (Specialized, Requires Contractor)

  • Specialized procedure for drilling a hole in a live, pressurized pipe (requires highly specialized equipment and training)
  • Typically requires mechanical contractor with hot tapping expertise
  • Used when system cannot be drained or taken offline
  • CRITICAL SAFETY: Only qualified, experienced personnel with proper safety protocols should perform hot tapping.

STEP 3: Install Flow Switch

  1. Apply Teflon tape to switch threads (3-4 wraps, clockwise)
    • Or use pipe dope per manufacturer
  2. Thread switch into Tee or boss
  3. Orient switch:
    • Arrow on switch points in flow direction (critical)
    • Electrical connection accessible for wiring
    • Paddle perpendicular to flow (not parallel)
  4. Tighten switch:
    • Hand tight, then 1-2 turns with wrench
    • Do not overtighten - can crack housing
  5. Verify paddle moves freely:
    • Gently push paddle (if accessible)
    • Should return to rest position

STEP 4: Set Flow Setpoint

  • Adjustable models:
    • Rotate adjustment dial to desired flow rate (gpm or ft/sec)
    • Typical setting: 1-2 ft/sec for proof of flow
    • Consult pump curve for expected flow
  • Fixed models:
    • Verify setpoint adequate for application
    • Typically 0.5-1.0 ft/sec factory set

STEP 5: Wire Flow Switch

  1. Locate terminal compartment on switch
  2. Remove cover (may require screwdriver)
  3. Identify terminals:
    • COM (Common)
    • NO (Normally Open) - Closes when flow present
    • NC (Normally Closed) - Opens when flow present
  4. Connect to controller:
    • Use NO contact for proof of flow:
      • NO → Controller BI
      • COM → Controller COM
    • Flow present = Contact closed = TRUE/1
    • No flow = Contact open = FALSE/0
  5. Tighten terminal screws: 7-9 in-lbs
  6. Route wiring away from hot pipes
  7. Reinstall terminal cover (weatherproof seal)

STEP 6: Pressure Test and Restore

  1. Close all drain valves
  2. Slowly open isolation valves:
    • Open upstream valve 1/4 turn, check for leaks
    • If no leaks, fully open upstream valve
    • Repeat for downstream valve
  3. Check for leaks at switch installation
    • Tighten if minor seepage (1/4 turn max)
    • If significant leak: Close valves, remove switch, reapply sealant
  4. Verify system pressure normal (30-150 PSI typical)
  5. Start pump (coordinate with operator)

STEP 7: Label

  • Example: “PUMP-1-FLOW” or “CHW-FLOW”
  • Label at both switch and controller

POST-INSTALL

  • Flow switch installed with arrow in flow direction
  • No leaks at installation (verified under pressure)
  • Setpoint configured appropriately
  • Wiring terminated tight
  • Terminal cover reinstalled (weatherproof)
  • Labels applied
  • System pressure normal
  • Photos taken

EXPECTED READINGS

NO FLOW (Pump OFF or Valves Closed)

  • Contact State: Open (NO) or Closed (NC)
  • Controller Reading: FALSE/0 (using NO contact)
  • Paddle Position: At rest (spring returns paddle)

FLOW PRESENT (Pump Running, Normal Flow)

  • Contact State: Closed (NO) or Open (NC)
  • Controller Reading: TRUE/1 (using NO contact)
  • Paddle Position: Deflected by flow (overcoming spring)
  • Typical Flow: 2-8 ft/sec in HVAC piping

FLOW SETPOINT

  • Proof of Flow: 0.5-1.5 ft/sec (low setpoint, confirms pump running)
  • Minimum Flow Alarm: 1.5-3.0 ft/sec (detects low flow condition)
  • Target Flow: 3-8 ft/sec typical for HVAC (consult pump curve)

PROOF OUT TESTS

TEST 1: No Flow Test

  • Do: Pump off, valves closed, no flow
  • Expect:
    • Contact open (NO) = FALSE
    • Controller shows “No Flow”
  • Pass If: Switch correctly shows no flow

TEST 2: Flow Established Test

  • Do: Start pump, establish flow
  • Expect:
    • Contact closes (NO) within 2-5 seconds
    • Controller changes to “Flow” or TRUE/1
    • Pump current increases (verify with clamp meter)
  • Pass If: Switch detects flow when pump starts

TEST 3: Flow Stoppage Test

  • Do: Close downstream valve (simulate flow stoppage)
  • WARNING: Don’t leave valve closed long (pump deadhead)
  • Expect:
    • Contact opens (NO) = FALSE after 2-5 seconds
    • Controller shows “No Flow” alarm
  • Pass If: Switch detects loss of flow
  • Immediately: Reopen valve after test

TEST 4: Minimum Flow Test

  • Do: Throttle flow with valve to minimum
  • Expect: Switch triggers at setpoint flow rate
  • Pass If: Triggers appropriately at setpoint

TEST 5: Leak Test

  • Do: Inspect all connections under full pressure
  • Expect: No water seepage or leaks
  • Pass If: Completely dry after 30 minutes operation

TEST 6: Integration with BAS

  • Switch appears in controller BI list
  • Flow/no-flow status displays correctly
  • Graphics show flow status
  • Pump interlock logic works (alarm if pump on but no flow)
  • No communication errors

TROUBLESHOOTING

FLOW SWITCH NEVER SHOWS FLOW (Always FALSE)

  1. Verify pump is running:
    • Check pump current with clamp meter
    • Hear pump motor running
    • If pump not running: Pump problem, not switch
  2. Check for actual flow:
    • Feel pipe vibration (flow present)
    • Check pressure gauges (ΔP indicates flow)
    • If no flow with pump running: Closed valve, air lock, or pump issue
  3. Check flow switch orientation:
    • Arrow must point in flow direction
    • If reversed: Flow pushes paddle closed (wrong way)
  4. Check setpoint:
    • May be set too high for actual flow
    • Reduce setpoint and retest
  5. Check paddle:
    • Paddle may be stuck or broken
    • Remove switch (isolate system first), inspect paddle
  6. Test contact:
    • Manually push paddle, measure contact continuity
    • If no continuity when paddle pushed: Switch failed

FLOW SWITCH ALWAYS SHOWS FLOW (Always TRUE)

  1. Check for actual flow:
    • Pump may be running (expected)
    • If pump off but shows flow: False reading
  2. Check wiring:
    • NC contact may be wired instead of NO
    • Wires may be crossed or shorted
  3. Test contact:
    • Disconnect wiring, measure contact with no flow
    • If contact closed with no flow: Switch failed or stuck

ERRATIC FLOW INDICATION (Cycling TRUE/FALSE)

  1. Air in system:
    • Air pockets cause intermittent paddle deflection
    • Vent system to remove air
  2. Turbulent flow:
    • Switch too close to elbow, valve, or pump
    • Relocate to straight section (10× pipe diameter)
  3. Vibration:
    • Pipe vibration causing paddle to flutter
    • Secure piping to reduce vibration
    • Increase switch time delay (if adjustable)
  4. Flow oscillation:
    • Pump cycling or VFD hunting
    • Check pump and control system

LEAKING AT FLOW SWITCH

  1. Minor seepage:
    • Tighten switch 1/4 turn
    • Do not overtighten (can crack housing)
  2. Persistent leak:
    • Remove switch, inspect threads
    • Reapply Teflon tape (3-4 wraps) or pipe dope
    • Inspect O-ring or gasket (replace if damaged)
    • Reinstall and pressure test
  3. Crack in housing:
    • Replace switch (overtightened or defective)

DELAYED RESPONSE (Slow to Show Flow)

  1. Normal delay: 2-5 seconds typical for paddle to deflect
  2. Check setpoint: May be set too high, paddle struggles to reach
  3. Check paddle: May be corroded or sticky
    • Remove and clean (isolate system first)
  4. Reduce setpoint: If flow low, lower setpoint to 0.5 ft/sec

FALSE FLOW INDICATION (Shows Flow with No Pump)

  1. Gravity flow:
    • System on multiple levels, gravity flow possible
    • Install check valve to prevent reverse flow
  2. Paddle stuck:
    • Debris or corrosion holding paddle deflected
    • Remove switch, clean paddle, reinstall
  3. Contact stuck closed:
    • Switch failed, replace

ESCALATION - COMPLETE BEFORE CALLING

PRE-ESCALATION CHECKLIST

  • Verified pump actually running (current measurement)
  • Verified flow present (pipe vibration, pressure gauges)
  • Checked flow switch arrow points in flow direction
  • Tested contact manually (paddle pushed = contact change)
  • Verified wiring connections tight
  • Checked for leaks at installation
  • Inspected paddle for damage or obstruction
  • Documented setpoint setting
  • Taken photos of installation and orientation

PROVIDE THIS INFO

  • Flow Switch: [Mfg / Model / Pipe Size / Location]
  • Application: CHW / HW / Condenser water / Other
  • Pump Status: Running / Off / Variable speed ____%
  • Pump Current: _____ A (measured with clamp meter)
  • Flow Expected: _____ gpm (from pump curve)
  • Setpoint: _____ ft/sec or gpm
  • Arrow Direction: Verified in flow direction / Wrong / Unsure
  • Contact Status: Open / Closed / _____ ohms
  • Pressure: _____ PSI (supply) | _____ PSI (return) | ΔP _____ PSI
  • Symptoms: [Never shows flow, always shows flow, erratic, leaking]
  • Steps Taken: [Troubleshooting completed]

CONTACTS

  • Field Specialist: [Phone]
  • Plumber/Mechanical Contractor: [Phone] (if leak or system issue)
  • Programmer: [Phone] (if interlock logic issue)
  • Dispatch: [Phone]

COMMON ISSUES & TIPS

✓ Arrow direction CRITICAL: Must point in flow direction or won’t work
✓ Straight pipe required: Install 10× pipe diameter from elbows, valves, pumps
✓ Setpoint selection: 0.5-1.5 ft/sec for proof of flow, higher for minimum flow alarm
✓ Pipe size matters: Must match pipe size or flow velocity calculation wrong
✓ Air in system: Most common cause of erratic behavior - vent system
✓ Teflon tape application: 3-4 wraps clockwise, don’t overtighten switch
✓ No flow with pump running: Check for closed valves, air lock, pump cavitation
✓ Proof of operation: Use in interlock: “Alarm if pump ON but no flow >60 seconds”
✓ Freeze protection: “Alarm if temperature <40°F AND no flow”
✓ Low flow alarm: Set higher setpoint (3-5 ft/sec) to detect loss of flow
✓ Pressure vs flow: Pressure can be normal with no flow (closed valve) - flow switch needed
✓ Time delay: Add 30-60 second delay in controller to prevent nuisance alarms at startup

Typical Flow Velocities (HVAC Systems)

  • Chilled Water: 4-8 ft/sec
  • Hot Water: 2-6 ft/sec
  • Condenser Water: 5-10 ft/sec
  • Glycol (20%): 3-6 ft/sec
  • Proof of Flow Setting: 0.5-1.5 ft/sec (20-30% of target)

Document ID: SSO-FLOW-SWITCH-001
Revision: 1.0
Next Review: Dec 2026

SAFETY WARNING: Flow switch installation requires system isolation and draining. Coordinate with building operations and mechanical contractor. Improper installation can cause leaks and water damage.

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