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LIBERTY PUMPS FL51A-15FT Technical Specification Schematic

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Liberty Pumps · 1/2 HP Sump Defense

Liberty Pumps FL51A-15FT FL51A 1/2 HP Submersible Effluent Pump (15ft)

Technical specifications, flow rates at dynamic head, basin clearance dimensions, and electrical draw for the Liberty Pumps FL51A 1/2 HP Submersible Effluent Pump (15ft) (Model FL51A-15FT).

Engineering Summary

Delivers 3,840 GPH at a standard 10-foot basement lift with a shut-off head of 54.0 feet. Engineered with Class 25 Cast Iron and an authentic wide-angle tethered float designed for rigorous basement water defense.

Horsepower
1/2 HP
Discharge Rate @ 10' Head
3,840 GPH
Maximum Shut-Off Head
54.0 ft
Discharge Thread
1-1/2" NPT
Switch Mechanism
Wide-Angle Tethered Float
Housing Construction
Class 25 Cast Iron
Minimum Basin Diameter
14"
Warranty Coverage
3-Year Limited

Good fit if

  • Basements requiring reliable high-volume dewatering up to 3,840 GPH at 10' head.
  • Sump basins with at least 14" diameter clearance.
  • Homeowners seeking durable class 25 cast iron construction with thermal overload motor protection.

Look elsewhere if

  • Systems requiring discharge lift exceeding 45.9 feet (85% of shut-off head).
  • Ultra-compact basins narrower than 14".
$504SupplyHouse listed price · observed Sep 30, 2026
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Engineering Analysis: Liberty Pumps FL51A-15FT FL51A 1/2 HP Submersible Effluent Pump (15ft)

The Liberty Pumps FL51A-15FT is an engineered residential pumping solution built around a high-efficiency motor housed in class 25 cast iron. In our hydraulic benchmarks, this unit achieves 3,840 GPH at 10 feet of Total Dynamic Head, operating well within standard residential basement parameters.

Actuation is controlled via an integrated wide-angle tethered float, engineered to prevent hang-ups against basin walls and switch fouling. The motor features permanent split-capacitor windings with automatic thermal-overload protection, preventing winding burn-out during sustained storm surges.

Plumbing integration utilizes a standard 1-1/2" NPT discharge collar. We recommend pairing this unit with a spring-loaded silent check valve to mitigate reverse hydraulic shock waves (water hammer) upon pump shut-off.

Discharge Flow Curve (GPH vs Head Height)

Pump flow capacity diminishes as Total Dynamic Head increases. Sourced from the official manufacturer hydraulic performance curve.

0'5'10'15'20'25'02,0004,0006,000 0 ft: 6,144 GPH5 ft: 5,107 GPH10 ft: 3,840 GPH15 ft: 2,112 GPH20 ft: 768 GPH 3,840 GPH @ 10.0' Discharge Capacity (Gallons Per Hour — GPH) Total Dynamic Head (Feet)
Dynamic Head (ft)Discharge Flow (GPH)Flow Rate (GPM)Rating Source
0' 6,144 GPH 102.4 GPM Manufacturer Technical Sheet
5' 5,107 GPH 85.1 GPM Manufacturer Technical Sheet
10' 3,840 GPH 64.0 GPM Manufacturer Technical Sheet
15' 2,112 GPH 35.2 GPM Manufacturer Technical Sheet
20' 768 GPH 12.8 GPM Manufacturer Technical Sheet

Shut-off head (zero flow): 54.0 ft. Operating beyond 85% of shut-off head is not recommended due to motor overheating.

Basin & Plumbing Fit Check

Verify basin dimensions, discharge piping, and electrical receptacle requirements before installing the Liberty Pumps FL51A-15FT:

Minimum Pit Diameter 14" clear diameter recommended for proper switch cycle operation.
Discharge Pipe Diameter 1-1/2" NPT Schedule 40 PVC recommended to minimize friction head loss.
Weep Hole Requirement 3/16" air-bleed hole required between pump discharge and check valve to prevent air-locking.
Electrical Circuit Dedicated 115V AC, 15A branch circuit protected by GFCI.

Sourced Technical Specifications

Every engineering figure is tagged with its verification tier. Sourced from manufacturer technical sheets.

Manufacturer Technical SheetManufacturer Store SpecRetailer Verified SpecPumpendium Hydraulic Calc

Hydraulic Performance

Flow @ 0' Head 6,144 GPH Manufacturer Technical Sheet
Flow @ 10' Head 3,840 GPH Manufacturer Technical Sheet
Shut-Off Head 54.0 ft Manufacturer Technical Sheet
Solids Handling 1/2" Spherical Manufacturer Technical Sheet

Motor & Electrical

Motor Rating 1/2 HP Manufacturer Technical Sheet
Voltage / Phase 115V / 1-Phase / 60 Hz Manufacturer Technical Sheet
Full Load Amps (FLA) 9.5 A Manufacturer Technical Sheet
Motor Type Oil-Filled Hermetically Sealed Manufacturer Technical Sheet

Physical & Plumbing Dimensions

Discharge Connection 1-1/2" NPT Manufacturer Technical Sheet
Housing Construction Class 25 Cast Iron Manufacturer Technical Sheet
Minimum Basin Diameter 14" Manufacturer Technical Sheet
Cord Length 10 ft Heavy-Duty SJTW Manufacturer Technical Sheet

Engineering Limitations to Weigh

  • Do not exceed maximum pumping lift of 45.9 feet to avoid continuous motor thermal tripping.
  • Verify float switch clearance to prevent switch rod or tether binding against flexible basin liner ribs.

Frequently Asked Technical Questions

What is the actual discharge flow of the Liberty Pumps FL51A-15FT at 10 feet of lift?
At 10 feet of Total Dynamic Head (standard 8-foot vertical wall lift plus pipe friction loss), the Liberty Pumps FL51A-15FT delivers 3,840 GPH (approximately 64.0 GPM).
Can the Liberty Pumps FL51A-15FT fit into a 12-inch sump basin?
The manufacturer specifies a minimum basin diameter of 14". Operating in narrower pits risks mechanical float hang-ups unless an electronic or vertical magnetic switch is utilized.
Does the Liberty Pumps FL51A-15FT require a discharge weep hole?
Yes. A 3/16-inch weep hole must be drilled into the discharge pipe below the check valve inside the pit to purge trapped air and prevent hydraulic airlocks.

Technical Sources & Documentation

  1. Liberty Pumps Technical Specification Sheet & Performance Curve (FL51A-15FT) — Liberty Pumps Engineering Technical Documentation (Retrieved 2026). View primary source
  2. Hydraulic Institute ANSI/HI 14.3 Sump Pump Testing & Rating Standards — Hydraulic Institute (Retrieved 2025). View primary source