How To Prime A Deep Well Jet Pump: A Step-by-Step Guide To Restoring Water Pressure

Priming a deep well jet pump involves completely filling the pump housing, suction line, and drive pipe with clean water to eliminate trapped air pockets and initiate hydraulic suction. This technical procedure requires isolating the electrical supply, filling the system through the priming port until water overflows, sealing the connections to be completely airtight, and cycling the motor to establish operational pressures between 30 and 50 PSI. Successful priming depends on a fully functioning foot valve at the bottom of the well to hold the water column in place.

Unlike shallow well pumps that draw water from depths of 25 feet or less using a single suction pipe, deep well jet pumps operate on a two-pipe system capable of retrieving water from depths down to 110 feet. This configuration utilizes a drive pipe to force water down into an ejector body (jet assembly) and a suction pipe to carry the pressurized water back up to the surface. Because air is highly compressible, any pocket of air inside this dual-pipe loop or the pump impeller housing will break the hydraulic seal, causing the pump to spin uselessly—a condition known as running dry. Understanding how to systematically purge this air and lock in a solid water column is essential for maintaining home water access and protecting your equipment from thermal damage.

Pre-Operation Planning & Equipment Checklist

Before beginning the priming process, you must verify the structural setup of your well system. Deep well jet pumps sit above ground and rely on a foot valve—a spring-loaded one-way check valve installed at the bottom of the piping inside the well casing. If the foot valve is leaking or jammed open with sediment, water will drain out of the pipes as fast as you pour it in, making priming impossible.

Ensure you have a reliable, external source of clean, potable water. Since your home water system is offline, you must transport water to the well site using buckets or a pressurized auxiliary tank. Do not use dirty stream or pond water, as suspended solids can clog the narrow venturi nozzle inside the deep well ejector package, requiring you to pull hundreds of feet of pipe to clear the blockage.

Tool, Material, and Specification Requirements

• Essential Gear and Tools:

  
  
  
  • Pipe wrench (14-inch or 18-inch, depending on piping scale)
  • Adjustable wrench or socket set for the priming plug
  • PTFE (Teflon) thread sealant tape or high-grade pipe joint compound
  • Large funnel with a flexible neck
  • 5 to 15 gallons of clean, potable water
  • Multi-meter (to verify power isolation)
  • Replacement pressure gauge (0–100 PSI range, if the existing gauge is corroded or unresponsive)

• Mandatory Prerequisite Knowledge:

  
  
  
  • Maximum Draw Depth: Deep well jet pumps are rated for specific depths (typically 25 to 110 feet). Running a pump beyond its rated depth will cause cavitation.
  • Electrical Safety: Operating around water and 115V/230V electrical connections presents severe shock hazards. Always isolate the pump's circuit breaker before removing any mechanical plugs.

• Estimated Operational Benchmarks:

  
  
  
  • Budget: $15 to $40 for basic consumables (PTFE tape, clean water, minor hand tools).
  • Duration: 45 minutes to 2 hours, depending on system depth and the number of priming cycles required to purge all air.

Step-by-Step Deep Well Jet Pump Priming Protocol

Follow these sequential instructions to safely evacuate air from your two-pipe system and re-establish your water pressure loop.

Step 1: Isolate Electrical Power and Relieve System Pressure

Locate the dedicated double-pole circuit breaker in your electrical service panel labeled "Well Pump" and switch it to the "Off" position. Lock or tag the panel to prevent accidental reactivation. Go to the pressure tank and open a nearby faucet or the tank’s bottom drain valve to bleed off any remaining pressurized water in the system. Verify that the system pressure gauge reads 0 PSI before proceeding.

Warning: Never attempt to loosen a priming plug or service a pump while the system is under pressure or connected to live electrical power. Rapid pressure release can eject brass fittings with extreme force, and automated pressure switches can kick on unexpectedly.

Step 2: Locate and Remove the Priming Plug

Identify the cast iron or bronze priming plug situated on the very top of the pump casing or on the discharge tee assembly immediately above the pump. This is typically a 1/2-inch or 3/4-inch square-head or hex-head NPT (National Pipe Thread) plug. Use a fitted wrench or socket to slowly back the plug out. If the plug is seized due to rust or mineral scale, apply a penetrating lubricant and let it sit for 10 minutes before applying steady, even counter-clockwise pressure to avoid shearing the plug.

Step 3: Fill the Pump Housing and Well Piping

Insert your funnel into the open priming port. Slowly and steadily pour clean, potable water into the pump. Because you are priming a two-pipe system, the water must flow down through both the drive pipe and the suction pipe, filling the entire vertical column down to the foot valve, as well as filling the internal impeller housing.

This stage requires patience. Water will displace air, causing bubbling and gurgling at the priming port. Stop pouring periodically to allow the air bubbles to escape, then resume. Continue this process until the water level rises to the very top of the priming port and remains completely stationary for at least two minutes. If the water level continually drops without stabilizing, your foot valve at the bottom of the well is likely leaking or stuck open.

Pro-Tip: If the system takes more than 15 gallons of water without filling up and you suspect the foot valve is functional but dry, the valve may require a back-pressure seal. Gently tapping the well pipes can sometimes help seat a stubborn spring-loaded foot valve.

Step 4: Seal the Priming Port with Thread Tape

Inspect the threads of the priming plug you removed in Step 2. Use a wire brush to clean away any old thread sealant, rust, or debris. Wrap the threads clockwise with 3 to 5 wraps of heavy-duty PTFE thread sealant tape, or apply a thin, even coat of non-hardening pipe joint compound. Carefully thread the plug back into the priming port by hand to ensure no cross-threading occurs, then tighten it securely with your wrench. The seal must be completely airtight; even a microscopic air leak will draw air into the pump head during operation, destroying the vacuum and causing the pump to lose prime.

Step 5: Restrict the Control Valve and Restore Power

Most deep well jet pump installations feature a control valve (often a gate valve or ball valve) on the discharge line leading to the pressure tank. Partially close this valve so it is roughly 80% shut. Restricting the discharge flow creates backpressure inside the pump housing when it starts, which forces water down the drive pipe to activate the jet ejector assembly in the well, speeding up the air-purging process. Once the valve is adjusted, return to your electrical panel and restore power to the pump circuit.

Step 6: Cycle the Pump and Monitor Pressure

As soon as the motor starts, watch the pressure gauge mounted on the pump body. If the pump is successfully primed, the pressure gauge should quickly rise and stabilize between 30 and 50 PSI.

• If the pressure rises, slowly open the discharge control valve in small increments over several minutes to allow water to flow into the pressure tank while forcing any remaining micro-bubbles out of the system.
• If the pressure fails to rise within 45 to 60 seconds, or if the needle flutters wildly near zero, the pump is still airbound. Turn off the power immediately to prevent the shaft seal from overheating. Let the pump cool for 10 minutes, then repeat Steps 2 through 6.

Technical Specifications & Priming Performance Matrix

The following table outlines the key mechanical, operational, and physical parameters governing the priming and operational phases of a standard two-pipe deep well jet pump system.

Common Hydraulic Failures & Field Remedies

System priming can fail due to worn mechanical parts or atmospheric leaks. Below are real-world failure modes encountered during deep well pump priming, along with diagnostic pathways and physical remedies.

• The system takes infinite water during filling and never fills to the priming port.

  
  
  
  • Root Cause: The foot valve at the bottom of the well casing is jammed open by sediment, mineral scaling, or has suffered physical spring failure, allowing all priming water to drain directly back into the aquifer.
  • Actionable Fix: You must pull the drop pipes out of the well casing to access the ejector assembly. Unscrew the damaged foot valve, clear any debris from the screen, and install a lead-free brass spring-loaded foot valve. Re-lower the pipes and repeat the priming process.

• The pump motor runs, pressure rises to 20 PSI, but then drops back to zero.

  
  
  
  • Root Cause: A micro-vacuum leak exists on the suction pipe connections or around the priming plug threads. Under suction, the pump draws in outside air rather than water, breaking the hydraulic vacuum.
  • Actionable Fix: Turn off power. Inspect all above-ground joints on the suction line. Apply soapy water to the joints while the system is under minor pressure to check for bubbles, or re-wrap the priming plug and all suction-side threaded fittings with fresh PTFE tape. Tighten all hose clamps on flexible poly pipe if applicable.

• The pump successfully primes but loses its prime completely within a few hours of sitting idle.

  
  
  
  • Root Cause: A slow leak in either the foot valve or a hairline split in the underground portion of the suction/drive piping is allowing gravity to slowly drain the water column back down into the well over time.
  • Actionable Fix: Install a check valve on the suction line immediately before the pump inlet as a temporary diagnostic measure. If the pump now holds its prime, the leak is verified to be underground or down-well. Pull the well lines to check for cracked fittings, or replace the faulty foot valve.

Frequently Asked Questions

Why does my deep well pump keep losing its prime?

A deep well pump loses its prime because air is entering the closed loop or water is escaping from it. The most common culprits are a failing, debris-clogged foot valve at the bottom of the well, a hairline crack in the drop pipes inside the well casing, or an imperfect, non-airtight seal around the priming plug or suction-side pipe fittings.

Can you damage a deep well pump by running it dry?

Yes, running a deep well jet pump dry for more than one minute can cause severe, irreversible damage to the pump. The water flowing through the pump acts as a coolant and lubricant for the internal mechanical shaft seal and plastic diffusers; without water, the friction generates intense heat that melts plastic components and ruins the shaft seals, leading to motor-damaging leaks.

How much water does it take to prime a deep well jet pump?

The volume of water required depends entirely on the depth of your well and the diameter of your drop piping. Because you must fill both the drive pipe and the suction pipe from the pump down to the foot valve, a well with a 100-foot depth typically requires between 8 to 12 gallons of water to completely fill the columns and pump housing.

How do I know if my foot valve is bad?

The clearest sign of a bad foot valve is the inability to fill the pump casing during the priming step. If you pour gallons of water into the priming port and the water level continuously drops without ever rising to the top, the foot valve is stuck open or leaking, allowing all your priming water to drain back into the well.

Can a submersible deep well pump lose its prime?

No, true submersible deep well pumps do not need to be primed because they operate entirely submerged in the well water at the bottom of the casing. Since the pump impellers are constantly flooded with water, they are self-priming and cannot pull air unless the water table drops below the pump intake level.

Professional Water System Engineering Support

If you have repeatedly attempted to prime your deep well jet pump without success, structural pipe failures or deep-well blockages may be preventing hydraulic circulation. Contact a certified professional water systems technician to conduct a diagnostic pressure test of your drop lines and safely restore your home's water supply.