Send a part number, a photo, or a whole BOM — we supply it and stand behind it. Worldwide shipping to 80+ countries.

3G Electric
RFQ CartGet a QuoteSign inSign up
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, Stainless Steel - Insertion-Style Switches for Liquids
McDonnell & MillerInsertion-Style Switches for Liquids

MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, Stainless Steel

The McDonnell & Miller FS4-3S is a paddle-type flow switch for liquids, designed as an insertion-style switch for 1-inch pipe sizes. It features a stainless steel construction with a 1-inch NPT connection and an SPDT…

SKU 3G-OTH-93473

Brand
McDonnell & Miller
Item
Flow Switch: Paddle, 1 in For Pipe Size, Stainless Steel
Category
Insertion-Style Switches for Liquids
Available to Order
Trade pricing by quote — replies within 24h
Qty
WhatsApp an engineer
No account needed — your quote request goes straight to our engineers. A free account lets you track quotes and re-order faster.
Worldwide Shipping
Air & sea freight
Datasheet on Request
Technical specs
1-Day Quote
Replies within 24h

Technical Specifications

McDonnell & Miller
Manufacturer Part Number
FS4-3S
Type
Stainless Steel, NPT, SPDT
NPT
1 in
For Pipe Size
1 in
Contact Rating (AC)
3.7 A @ 240V (Full Load)
View Full Spec Sheet

Technical Documents

No technical documents available for this product.
Request documentation →
Not sure this is the right part? Get a recommendation.

Need installation or engineering help?

Installation, commissioning, maintenance plans, system design, and bundled product + service quotes — one team handles the full scope.
Talk to an engineer

Ask a question

McDonnell & Miller Products
3G Electric (S) Pte. Ltd. — Singapore

Product Description

The McDonnell & Miller FS4-3S is a paddle-type flow switch for liquids, designed as an insertion-style switch for 1-inch pipe sizes. It features a stainless steel construction with a 1-inch NPT connection and an SPDT contact rated at 3.7 A at 240V full load AC.

Frequently Asked Questions

What is the McDonnell & Miller FS4-3S flow switch used for?

The McDonnell & Miller FS4-3S is a paddle-type flow switch used to detect liquid flow or no-flow conditions in piping systems. It is commonly applied in HVAC, boiler, and industrial process lines to protect pumps, chillers, and heat exchangers from damage due to insufficient flow.

What are the specifications of the McDonnell & Miller FS4-3S?

The FS4-3S is an insertion-style flow switch for 1-inch pipe sizes. It has a stainless steel body with a 1-inch NPT connection and an SPDT contact rated at 3.7 A at 240V AC full load. The manufacturer part number is FS4-3S, and it is made by McDonnell & Miller.

Where to buy the McDonnell & Miller FS4-3S worldwide?

You can source the McDonnell & Miller FS4-3S through 3G Electric, a global industrial equipment distributor. We handle full logistics, customs clearance, and delivery to worldwide destinations. Contact us for availability and lead time; we supply genuine McDonnell & Miller components.

How to install a McDonnell & Miller FS4-3S paddle flow switch?

Install the FS4-3S in a horizontal pipe section with the paddle oriented correctly for flow direction. Ensure the pipe is 1-inch NPT and the switch is wired per the SPDT contact rating (3.7 A at 240V AC). Follow standard piping practices and consult the manufacturer's manual for proper paddle selection and adjustment.

Used in

Common applications for McDonnell & Miller
Steam boiler low-water cutoff — McDonnell & Miller inline flow switches (e.g., FS-1) for automatic burner shutdown
Cooling water flow monitoring — McDonnell & Miller insertion-style switches (e.g., FS4-3D) in large-diameter pipes
Hazardous-area process lines — McDonnell & Miller FS7-4E with NEMA 7/9 enclosure for Class I, Div 1 locations
HVAC chilled water systems — McDonnell & Miller FS6-1 inline switch for pump flow verification
Industrial wastewater treatment — McDonnell & Miller FS4-3S stainless steel switch for corrosive fluid flow detection
Boiler feedwater control — McDonnell & Miller FS8-WJ with BSP connections for international installations

McDonnell & Miller Products

3G Electric supplies McDonnell & Miller insertion-style switches for liquids. We supply genuine products with in-stock availability on common SKUs, technical documentation, commissioning support, and warranty service — worldwide.

You might also need

Burners & Combustion →Pumps & Compressors →Spare Parts →All Products →

Similar products

Matched by specification & description
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1-1/4 in; Contact Rating (AC): 44.4 A @ 120V (Locked Rotor).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1-1/4 in; Contact Rating (AC): 44.4 A @ 120V (Locked Rotor).
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in NPT, 1 in Connection Size, NPT (MPN FS4-3). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 44.4 A @ 120V (Locked Rotor).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in NPT, 1 in Connection Size, NPT (MPN FS4-3). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 44.4 A @ 120V (Locked Rotor).
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in NPT, 1 in Connection Size, NPT (MPN FS4-3T3-1). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 3.7 A @ 240V (Full Load).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in NPT, 1 in Connection Size, NPT (MPN FS4-3T3-1). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 3.7 A @ 240V (Full Load).
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in BSP, 1 in Connection Size, BSP (MPN FS8-WJ). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 7.4 A @ 120V (Full Load).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in BSP, 1 in Connection Size, BSP (MPN FS8-WJ). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 7.4 A @ 120V (Full Load).

More from McDonnell & Miller

View all McDonnell & Miller parts →
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4W). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1-1/4 in; Hazardous Location Rating: Class I, Div 1 and 2, Group C, D; Contact Rating (AC): 7.4 A @ 120V (Full Load).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4W). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1-1/4 in; Hazardous Location Rating: Class I, Div 1 and 2, Group C, D; Contact Rating (AC): 7.4 A @ 120V (Full Load).
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4SW). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 16 in; Hazardous Location Rating: Class II, Div 1 and 2, Group E, F, G; Contact Rating (AC): 7.4 A @ 120V (Full Load).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4SW). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 16 in; Hazardous Location Rating: Class II, Div 1 and 2, Group E, F, G; Contact Rating (AC): 7.4 A @ 120V (Full Load).
MCDONNELL & MILLER General Purpose Switch: Paddle, 1 in/6 in For Pipe Size, Brass, 1 in NPT, NPT (MPN FS251). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 6 in; Contact Rating (AC): 44.4 A @ 120V (Locked Rotor).
McDonnell & Miller
MCDONNELL & MILLER General Purpose Switch: Paddle, 1 in/6 in For Pipe Size, Brass, 1 in NPT, NPT (MPN FS251). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 6 in; Contact Rating (AC): 44.4 A @ 120V (Locked Rotor).
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4S). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1-1/4 in; Contact Rating (AC): 22.2 A @ 240V (Locked Rotor).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4S). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1-1/4 in; Contact Rating (AC): 22.2 A @ 240V (Locked Rotor).
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in NPT, 1 in Connection Size, NPT (MPN FS4-3D). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 22.2 A @ 240V (Locked Rotor).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in NPT, 1 in Connection Size, NPT (MPN FS4-3D). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 22.2 A @ 240V (Locked Rotor).
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4E). Key specifications — Brand: MCDONNELL & MILLER; Switch Enclosure: NEMA 7/9; For Pipe Size: 16 in; Hazardous Location Rating: Class I, Div 1 and 2, Group C, D; Contact Rating (AC): 7.4 A @ 120V (Full Load).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 1/4 in/16 in For Pipe Size, Brass, 1 1/4 in NPT, NPT, SPDT (MPN FS7-4E). Key specifications — Brand: MCDONNELL & MILLER; Switch Enclosure: NEMA 7/9; For Pipe Size: 16 in; Hazardous Location Rating: Class I, Div 1 and 2, Group C, D; Contact Rating (AC): 7.4 A @ 120V (Full Load).
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in NPT, 1 in Connection Size, NPT (MPN FS4-3RP-T). Key specifications �— Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 44.4 A @ 120V (Locked Rotor).
McDonnell & Miller
MCDONNELL & MILLER Flow Switch: Paddle, 1 in For Pipe Size, 1 in NPT, 1 in Connection Size, NPT (MPN FS4-3RP-T). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 44.4 A @ 120V (Locked Rotor).
MCDONNELL & MILLER General Purpose Switch: Paddle, 1 in/6 in For Pipe Size, Brass, 1 in NPT, NPT (MPN FS254). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 3.7 A @ 240V (Full Load).
McDonnell & Miller
MCDONNELL & MILLER General Purpose Switch: Paddle, 1 in/6 in For Pipe Size, Brass, 1 in NPT, NPT (MPN FS254). Key specifications — Brand: MCDONNELL & MILLER; For Pipe Size: 1 in; Contact Rating (AC): 3.7 A @ 240V (Full Load).