🔧 Little Giant 3-MD-SC Magnetic Drive Pump — 1/12 HP 115V 750 GPH Seal-Less | 581503

Leak-proof magnetic drive technology for chemical-resistant spa and industrial circulation

💧 Product Overview

The Little Giant 3-MD-SC is a seal-less magnetic drive centrifugal pump designed for in-line, non-submersible circulation of semi-corrosive chemicals and solutions. Unlike traditional spa circulation pumps that use a mechanical shaft seal, the 3-MD-SC uses magnetic drive coupling — the motor magnetically spins the impeller through the pump housing wall, completely eliminating the mechanical seal. This means zero seal leaks, ever.

Rated at 1/12 HP / 115V / 750 GPH at 1 foot of head, with a maximum shut-off head of 21.9 feet, this pump delivers strong circulation for its compact size. The 3/4″ FNPT inlet and 1/2″ MNPT discharge provide versatile plumbing connections using standard NPT pipe fittings. The pump head is rotatable for easy alignment with existing plumbing, and can be cleaned or serviced with no special tools.

All wetted components are built for chemical resistance: the volute, magnet housing, and impeller are glass-filled polypropylene, while the shaft and thrust washers are 99.5% pure alumina ceramic — providing excellent wear resistance. The nitrile (Buna-N) O-ring provides reliable sealing between components. The pump handles fluids up to 150°F (66°C) with a specific gravity up to 1.1.

The thermally protected 1/12 HP open fan-cooled motor comes with a 6-foot power cord and 3-prong molded plug — ready for immediate use out of the box. Factory preassembled and pretested by Little Giant (a Franklin Electric brand). Certified UR/C-CSA.

⚠️ IMPORTANT: This is a magnetic drive chemical transfer pump, not a traditional spa wet end pump. It uses NPT pipe thread connections (3/4″ FNPT inlet, 1/2″ MNPT discharge), not MBT union connections like Waterway or Gecko spa pumps. Verify your plumbing compatibility before ordering.

⭐ Key Features

• ✅ Seal-Less Magnetic Drive — Zero mechanical seal means zero seal leaks — ever
• ✅ 1/12 HP / 750 GPH at 1′ / 12.5 GPM Maximum — Strong flow with 21.9 ft maximum shut-off head
• ✅ Chemical Resistant Construction — Glass-filled polypropylene volute, housing, and impeller
• ✅ 99.5% Pure Alumina Ceramic — Shaft and thrust washers for exceptional wear resistance
• ✅ Rotatable Pump Head — Easy alignment with existing plumbing, no special tools required
• ✅ Thermally Protected Motor — Open fan-cooled with automatic thermal overload protection
• ✅ 6-Foot Power Cord with 3-Prong Plug — Ready to use out of the box
• ✅ 115V / 50/60 Hz — Compatible with standard US household power and international 50 Hz
• ✅ Handles Fluids up to 150°F (66°C) — Suitable for hot tub and heated spa water temperatures
• ✅ Non-Revolving Thrust Washers — Prevent shaft wear for longer service life
• ✅ Spindle Shaft Supported at Both Ends — Prevents impeller damage during start-up and stop
• ✅ Factory Preassembled and Pretested — Ready for immediate installation
• ✅ UR/C-CSA Certified — Safety listed for US and Canadian markets

⚙️ Technical Specifications

Specification	Value
Manufacturer	Little Giant (Franklin Electric)
Model	3-MD-SC
Part Number	581503
Pump Type	Magnetic Drive Centrifugal — Seal-Less
Drive Type	Magnetic Coupling (no mechanical shaft seal)
Motor Power	1/12 HP
Wattage	190W (per Parts4Tubs listing)
Voltage	115V
Frequency	50/60 Hz
Phase	Single Phase
Amperage	2.4A
Flow Rate	750 GPH (12.5 GPM) at 1 ft of head
Maximum Shut-Off Head	21.9 ft (6.6 m)
Inlet Port	3/4″ FNPT (Female National Pipe Thread)
Discharge Port	1/2″ MNPT (Male National Pipe Thread)
Volute Material	Glass-Filled Polypropylene
Impeller Material	Glass-Filled Polypropylene
Magnet Housing Material	Glass-Filled Polypropylene
Shaft Material	99.5% Pure Alumina Ceramic
Thrust Washer Material	99.5% Pure Alumina Ceramic
O-Ring Material	Nitrile (Buna-N)
Max Fluid Temperature	150°F (66°C)
Max Ambient Air Temperature	77°F (25°C)
Specific Gravity (Max)	1.1
Motor Type	Thermally Protected, Open Fan-Cooled
Motor Number	977458
Power Cord	6 ft with 3-prong molded plug — INCLUDED
Pump Head	Rotatable — no special tools required
Weight	8.5 lbs
Submersible	No — In-Line Use ONLY
Self-Priming	No — Must be flooded suction
Run Dry	❌ Do NOT run SC models dry
Certification	UR/C-CSA

Performance Curve (at 60 Hz)

Head	Flow Rate
1 ft	750 GPH
3 ft	710 GPH
6 ft	665 GPH
9 ft	600 GPH
15 ft	425 GPH
21.9 ft	0 GPH (Shut-Off)

💡 MOTOR BEARING NOTE: The Little Giant manufacturer website describes this pump as having “ball bearings,” while some distributors list “sleeve bearings.” Verify against the nameplate or contact Little Giant/Franklin Electric for the current production specification.

⚡ Electrical Requirements

Electrical Spec	Requirement
Supply Voltage	115V
Frequency	50/60 Hz
Phase	Single Phase
Amperage	2.4A
Recommended Fuse	2.0A (if fused-type plug is used)
Power Cord	6 ft with 3-prong molded plug — INCLUDED

⚠️ IMPORTANT:

All electrical work must be performed by a licensed electrician in accordance with the National Electrical Code (NEC) and local building codes. Hot tubs require GFCI (Ground Fault Circuit Interrupter) protection. A dedicated circuit is required — do not share with other appliances.

💡 230V VERSION AVAILABLE: For 230V applications, the Little Giant 3-MD-SC is also available as model 581513 (230V, 1.7A, 60Hz). Same pump, different voltage.

🔩 How Magnetic Drive Works — Why No Seal Leaks

Traditional spa pumps use a mechanical shaft seal where the motor shaft passes through the pump housing into the wet end. This seal eventually wears and leaks — it’s the most common failure point on any circulation pump.

The Little Giant 3-MD-SC eliminates this entirely. The motor spins an outer magnet on the dry side of the pump housing. This outer magnet magnetically couples to an inner magnet attached to the impeller inside the sealed wet end. The impeller spins without any shaft penetrating the pump housing wall.

Result: There is physically no opening for water to leak through. No seal to wear. No seal to replace.

Trade-off: Magnetic drive pumps should NOT be run dry (SC models). Running dry causes the ceramic bearings to overheat without fluid lubrication. Always ensure flooded suction before operating.

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🔄 Compatibility & Connection Guide

Port Connections

Port	Size	Thread Type	Location
Inlet (Suction)	3/4″	FNPT (Female NPT)	—
Discharge	1/2″	MNPT (Male NPT)	—

⚠️ NPT CONNECTIONS — NOT MBT: This pump uses standard National Pipe Thread (NPT) fittings, NOT male buttress thread (MBT) unions like Waterway Tiny Might, Iron Might, or Uni-Might pumps. You will need NPT-compatible plumbing fittings and adapters. Use appropriate thread sealant (Teflon tape or pipe dope) on NPT connections.

3-MD-SC Model Variants

Part Number	Voltage	Amperage	Frequency	Connection	Flow
581503 (This Pump)	115V	2.4A	50/60 Hz	3/4″ FNPT in / 1/2″ MNPT out	750 GPH at 1 ft
581513	230V	1.7A	60 Hz	3/4″ FNPT in / 1/2″ MNPT out	750 GPH at 1 ft

Applications

This pump is designed for circulation of semi-corrosive chemicals and solutions, including:

• Moderately corrosive acids and alkalis
• Solvents and brine solutions
• Plating solutions
• Sterile solutions
• Hot tub / spa water circulation (where NPT connections are used)
• Any fluid compatible with glass-filled polypropylene, alumina ceramic, and nitrile (Buna-N)

💡 CHEMICAL RESISTANCE: Little Giant provides a comprehensive Chemical Resistance Chart to verify compatibility with your specific fluid. Download from the manufacturer resources section below.

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🔗 Part Numbers & Cross-References

Primary Part Numbers

Part Number	Description
581503	Parts4Tubs SKU / Little Giant Part Number (115V)
3-MD-SC	Little Giant Model Name
977458	Motor Number

Related Models

Part Number	Description
581513	3-MD-SC 230V version (1.7A) — same pump, different voltage

Replacement Parts

Part Number	Description
977458	Replacement motor for 581503 (115V 50/60 Hz)

💡 Pumping heads are easily rotated, cleaned, or serviced with no special tools. The pump is factory preassembled and pretested — no assembly required for new installations.

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🛠️ Installation Requirements

Mounting & Placement

Requirement	Specification
Position	In-line, non-submersible — must be in a DRY area
Suction	Flooded suction required — inlet must be below liquid surface level
Protection	Protected from splash — pump is NOT waterproof
Ambient Temperature	Maximum 77°F (25°C)
Ventilation	Ensure adequate airflow for open fan-cooled motor

Plumbing

Connection	Size	Thread Type
Inlet	3/4″	FNPT (Female NPT)
Discharge	1/2″	MNPT (Male NPT)
Thread Sealant	Teflon tape or pipe dope recommended on NPT threads

Pump Head Rotation

The pump head (volute) can be rotated to align inlet and discharge with your plumbing. Loosen the wing nuts, rotate the head, and retighten. Do NOT use excessive force — this may damage the plastic parts. Ensure wing nuts are tight before operating.

Installation Notes

⚠️ This pump is NOT submersible — install in a dry location only, protected from splash.

⚠️ Inlet must be below the liquid surface level (flooded suction) before starting.

⚠️ Do NOT run SC models dry — running without fluid damages ceramic bearings.

⚠️ Maximum fluid temperature: 150°F (66°C). Maximum ambient air temperature: 77°F (25°C).

⚠️ GFCI protection is required by the National Electrical Code (NEC) for all hot tub installations.

⚠️ Verify motor nameplate electrical data matches your supply before operating.

⚠️ If using a fused-type plug, a 2.0A fuse is recommended.

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⚙️ Maintenance Guide

Routine Maintenance

Task	Frequency	Notes
Check for leaks at connections	Monthly	NPT fittings only — no shaft seal to leak
Verify water flow	Monthly	Reduced flow indicates clogging or bearing wear
Inspect pump head	Quarterly	Check for cracks or chemical degradation
Clean pump head / impeller	As needed	Remove pump head — no special tools required
Check motor ventilation	Quarterly	Keep fan and vents clear of debris
Check amperage draw	Annually	Should read approximately 2.4A at 115V

Warning Signs — Service or Replace Pump If:

• Reduced or no water flow (impeller or bearing wear)
• Unusual noise (ceramic bearing wear)
• Motor overheating or tripping thermal protection
• Visible cracks in pump head or housing
• Chemical degradation of wetted components

Key Advantage — No Seal Replacement Needed

Unlike traditional spa pumps, the 3-MD-SC has no mechanical shaft seal to wear, leak, or replace. The most common maintenance is simply cleaning the pump head and checking the ceramic bearings for wear. The pump head is designed for tool-free removal and service.

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🎯 Ideal Applications

Application	Suitability	Notes
♨️ Spa/Hot Tub Circulation (NPT plumbing)	✅ Yes	Handles up to 150°F fluid, leak-proof design
♨️ Chemical-Treated Water Circulation	✅ Yes	Glass-filled polypropylene resists semi-corrosive chemicals
⚙️ Brine / Salt Solution Circulation	✅ Yes	Chemical-resistant construction
⚙️ Plating Solution Transfer	✅ Yes	Designed for semi-corrosive industrial fluids
⚙️ Sterile Solution Circulation	✅ Yes	Seal-less design prevents contamination
⚙️ Leak-Critical Installations	✅ Yes — Best Choice	Zero seal = zero seal leaks
🛁 Standard MBT Union Spa Plumbing	❌ No — Wrong Connection	Uses NPT threads, not MBT — needs adapters
🛁 Submersible Applications	❌ No — NOT Submersible	In-line use only, must be in a dry location
🛁 Dry-Run Applications	❌ No — Do NOT Run Dry	SC models require fluid for ceramic bearing lubrication

❓ Frequently Asked Questions

Q: What makes a magnetic drive pump different from a regular spa pump? A: A regular spa pump has a mechanical shaft seal where the motor shaft enters the wet end — this seal eventually wears and leaks. The 3-MD-SC uses magnetic coupling instead: the motor spins an outer magnet that magnetically drives the impeller inside a completely sealed housing. There is no shaft penetration, so there is physically no place for water to leak.

Q: Will this fit standard spa plumbing with union connections? A: This pump uses NPT pipe thread connections (3/4″ FNPT inlet, 1/2″ MNPT discharge), NOT MBT union connections. If your spa uses MBT unions (like most Waterway, Gecko, or Balboa installations), you will need NPT-to-barb or NPT-to-union adapters.

Q: What is the flow rate? A: 750 GPH (approximately 12.5 GPM) at 1 foot of head. Flow decreases as head increases — see the performance curve table above.

Q: Can I run this pump dry? A: No. The SC (Semi-Corrosive) model must NOT be run dry. The ceramic bearings require fluid for lubrication. Running dry will cause overheating and bearing damage. Always ensure the pump inlet is flooded before starting.

Q: What is the maximum water temperature? A: 150°F (66°C) fluid temperature, with a maximum ambient air temperature of 77°F (25°C). This is suitable for standard hot tub water temperatures.

Q: Is the power cord included? A: Yes. A 6-foot power cord with 3-prong molded plug is included — the pump is ready to use out of the box.

Q: Is there a 230V version? A: Yes. Model 581513 is the 230V version (1.7A, 60Hz). Same pump performance and construction, different voltage.

Q: Does this pump have a seal that needs replacing? A: No. That’s the primary advantage of magnetic drive — there is no mechanical shaft seal. The most common maintenance items are the ceramic bearings and the Nitrile O-ring between the pump head and housing.

Q: Can the pump head be rotated? A: Yes. The pump head is rotatable for easy plumbing alignment. Loosen the wing nuts, rotate, and retighten — no special tools required.

Q: What certifications does this pump have? A: UR/C-CSA — safety listed for US and Canadian markets.

Q: Do I need GFCI protection? A: Yes. GFCI protection is required by the National Electrical Code (NEC) for all hot tub and spa installations.

🏆 Why Choose the Little Giant 3-MD-SC

• ✅ Zero Seal Leaks — Magnetic drive means no mechanical seal to wear or fail
• ✅ Chemical Resistant — Glass-filled polypropylene and 99.5% alumina ceramic construction
• ✅ 750 GPH / 12.5 GPM — Strong circulation with 21.9 ft maximum head
• ✅ Handles 150°F Fluids — Suitable for hot tub water temperatures
• ✅ Plug-and-Play — 6-foot cord with 3-prong plug, factory preassembled and pretested
• ✅ 50/60 Hz Compatible — Works on US and international power supplies
• ✅ Tool-Free Service — Pump head rotates and disassembles without special tools
• ✅ Thermally Protected Motor — Automatic overload protection
• ✅ Dual-End Spindle Support — Prevents impeller damage during start-stop cycles
• ✅ Non-Revolving Thrust Washers — Reduces shaft wear for longer life
• ✅ Franklin Electric Brand — Backed by a major US pump manufacturer
• ✅ UR/C-CSA Certified — Safety listed for US and Canada

🤝 Why Buy from Parts4Tubs

• ✅ Fast shipping across the United States
• ✅ Expert advice from spa and hot tub specialists
• ✅ Competitive pricing
• ✅ Full warranty support
• ✅ Hassle-free returns
• ✅ Broad range of circulation pumps — magnetic drive and traditional
• ✅ Dedicated customer service team

✨ Summary

The Little Giant 3-MD-SC (581503) is a seal-less magnetic drive circulation pump delivering 750 GPH at 1 foot of head with a 1/12 HP, 115V/50-60Hz thermally protected motor. Its magnetic coupling eliminates the mechanical shaft seal entirely — meaning zero seal leaks throughout the pump’s lifetime. Built with glass-filled polypropylene and 99.5% alumina ceramic for chemical resistance, it handles fluids up to 150°F through 3/4″ FNPT inlet and 1/2″ MNPT discharge connections. Comes with a 6-foot power cord and 3-prong plug, factory preassembled and pretested. UR/C-CSA certified. 230V version available (581513). Order from Parts4Tubs today.