**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

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**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

- **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

- **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)

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- ☑ 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)

- ⚠️ **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

- [ ] **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

- [ ] 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)

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- 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

- 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)

- [ ] 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

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

- Use existing threaded opening in pipe

- Clean threads and apply Teflon tape

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

- 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.

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

* 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

* Verify setpoint adequate for application

* Typically 0.5-1.0 ft/sec factory set

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)

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)

- Example: "PUMP-1-FLOW" or "CHW-FLOW"

- Label at both switch and controller

- [ ] 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

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- **Contact State:** Open (NO) or Closed (NC)

- **Controller Reading:** FALSE/0 (using NO contact)

- **Paddle Position:** At rest (spring returns paddle)

- **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

- **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)

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- **Do:** Pump off, valves closed, no flow

- **Expect:**

* Contact open (NO) = FALSE

* Controller shows "No Flow"

- **Pass If:** Switch correctly shows no flow

- **Do:** Start pump, establish flow

* 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

- **Do:** Close downstream valve (simulate flow stoppage)

- **WARNING:** Don't leave valve closed long (pump deadhead)

* 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

- **Do:** Throttle flow with valve to minimum

- **Expect:** Switch triggers at setpoint flow rate

- **Pass If:** Triggers appropriately at setpoint

- **Do:** Inspect all connections under full pressure

- **Expect:** No water seepage or leaks

- **Pass If:** Completely dry after 30 minutes operation

- [ ] 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

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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

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

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

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)

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

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

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- [ ] 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

- **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]

- **Field Specialist:** [Phone]

- **Plumber/Mechanical Contractor:** [Phone] (if leak or system issue)

- **Programmer:** [Phone] (if interlock logic issue)

- **Dispatch:** [Phone]

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✓ **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

- **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)

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**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.