Troubleshooting Lake Pump Suction Line Issues: Prime Loss and Friction Loss

Troubleshooting Lake Pump Suction Line Issues: Prime Loss and Friction Loss

A 2 HP lake pump with a long, complex suction line may lose prime or suffer from excessive friction loss. This case involves 196 feet of 2-inch PVC with five 90° elbows and 5.5 feet of vertical rise.

System Configuration

• Pump to beach: 50 ft
• Beach to dock: 60 ft (90° elbow)
• Under dock: 2 ft up (90°), 80 ft horizontal (90°), 3.5 ft down (90°) to strainer
• Total: 196 ft, 5 elbows, 5.5 ft net rise

Symptoms

• Pump primes initially.
• Station starts but pump cannot maintain operation.
• Shuts down after running briefly.

Primary Suspect: Suction Line Leak (Loss of Prime)

Even a small air leak in the suction line will cause the pump to lose prime once the water column breaks. Common leak points:

• Threaded connections at pump and foot valve.
• Glue joints not properly primed/cemented.
• Foot valve clogged or not seating.

Test: Install a pressure gauge and shutoff valve on the suction side near the pump. Prime the system, close the shutoff valve, and watch the gauge. Pressure drop indicates a leak.

Secondary: Foot Valve Issues

• Foot valve lying on lake bottom can suck sediment.
• Solution: Mount foot valve in a milk crate suspended off the bottom. Cut a hole in the crate, insert foot valve, and lower it.

Friction Loss Analysis

At 18 GPM (typical for 6 rotary heads), 196 ft of 2-inch PVC has ~2 ft of friction loss—negligible for a 2 HP pump. Elbows add minimal loss if not leaking. The rise is within the pump's capability.

Mechanical Considerations

• Support the suction pipe at the pump with a hanger or bracket to prevent stress on the pump housing.
• Use a union or flange at the pump for easy removal.
• Ensure the pump is not oversized for the zone demand, which can cause cycling.

Action Plan

1. Pressure-test the suction line for leaks.
2. Inspect and elevate the foot valve.
3. Verify pump impeller condition if prime loss persists.