# 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.