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Inline Constant Water Pressure Systems
by Little Giant / Franklin Electric

Tired of waiting for that load of clothes in the washer to finish or the sprinklers to turn off before you can take a shower? These constant water pressure systems are the solution to your low water pressure problem! Increasing the flow when demand requires it can make completing everyday projects less taxing, and ease the stresses associated with lack of water pressure.

SubDrive Inline Constant Water Pressure System

Traditional municipal systems use city water lines to deliver water to your home. Water pressure may vary for homes due to a number of factors. Some of the more common causes of low water pressure are: old infrastructure, being located a long distance from the main water line or even being at the top of a hill. Fluctuating water pressure and flow can disrupt your daily life and make simple chores around the house difficult. These inline constant water pressure systems are installed on your main water line and connect to a pressure tank that feeds your whole house. As water demand picks up, the pump in the inline unit will pump faster keeping the pressure from dropping due to the increased water demand. These systems are a must have for anyone with inconsistent or low water pressure.

This compact water pressure system features:
  • Great for water storage/cistern systems, homes in private and municipal applications, general pressure boosting, sprinkler systems, farms, and commercial wash down systems
  • Stainless steel construction - made for years of operation - lead free design is compliant with new low lead laws
  • Small and compact design of the pump fits into small areas, even between floor joists
  • Can be mounted in any orientation for greater flexibility of installation
  • Quiet and cool operation - integrated motor design allows water to flow around it
  • Increases incoming pressure by up to 60 PSI
  • Wide range of pressure adjustment settings; 25-80 PSI
  • Factory pressure setting 50 PSI
  • Maximum operating temperature: 104° F.
  • Operates on a wide range of flows from flooded suction to 35 GPM
  • NEMA 4 electronics enclosure (liquid tight conduit and fittings must be used to maintain NEMA 4 rating)
  • 1.2 hp power, single phase, 230V, 12 amps maximum operating current
  • 1-1/4" female NPT outlet and inlets
  • Built-in sensor helps protect these systems from many common failures including: low water shut off, surge protection, voltage underload, locked pump, open circuit, short circuit, or an overheated controller

Please Note: This Inline Constant Pressure System requires a small pressure tank be installed on the pump outlet to maintain proper constant pressure. The pressure tank prevents water hammer and helps to prevent pressure spikes during sudden changes in water demands on the system. The pressure tank also provides water while the pump builds up speed and when only a small amount of water is needed for a short period of time. Pressure tanks are sold separately. Not sure what size you'll need? Learn more


Description Price & Quantity
SubDrive Inline 25GIL1100N4 Constant Water Pressure System $1,329.18
2.1 Gallon Pressure Tank #A101 for up to 12 gpm flow rate (factory pre-charge 35 psi)
8" diameter x 12-1/2" height - 3/4" MIPT inlet
$39.93
4.75 Gallon Pressure Tank #A102 for over 12 gpm flow rate (factory pre-charge 35 psi)
11" diameter x 15" height - 3/4" MIPT inlet
$49.88
Replacement Pressure Switch #305707906 $124.91
Optional Overpressure Switch (prevents over-pressurized system - not required for normal operation) $85.39
Adjustable Pressure Relief Valve - 3/4" inlet & outlet, brass construction (50-175 PSI) $46.79

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Inline 400 Pressure Boosting System

This compact water pressure system features:
  • Great for water storage/cistern systems, boosting city water delivery, general pressure boosting, repressurizing after filtration, and sprinkler system boosting
  • Simple flow-based controls mean you get the pressure you need every time while working with your existing plumbing system
  • Durable, lead free construction is compliant with regulations and provides years of reliable service
  • Slim, compact canister design of the pump fits into super small areas
  • Can be mounted vertically or horizontally for greater flexibility of installation
  • Rated only for indoor use - whisper-quiet operation is non-obtrusive
  • Increases incoming pressure by up to 55 PSI
  • Designed to automatically start boosting when discharge pressure drops below 40 PSI, but can be adjusted to meet your needs
  • Factory pressure setting 40 PSI
  • Maximum operating temperature: 120° F.
  • 1/3 hp power, single phase, 115V or 230V, 6.6 amps (115V) or 3.3 amps (230V) maximum operating current
  • 1" female NPT outlet and inlets
  • Built-in sensor helps protect the unit from many common failures including: dry run, voltage over/underload, or overheating
  • View detailed dimensions
  • View pump performance curve
  • View a typical installation diagram

Please Note: This Inline Pressure Boosting System requires a small pressure tank be installed on the pump outlet to minimize motor startup due to small flow demand or a minor leak in your water system. The pressure tank comes from the factory pressurized at the start pressure setting - it is recommended you charge the tank to 38 psi for this system. Pressure tanks are sold separately. Not sure what size you'll need? Learn more


Description Price & Quantity
Inline 400 Low Pressure Solution System - 115V $589.68
Inline 400 Low Pressure Solution System - 230V $589.78
2.1 Gallon Pressure Tank #A101 for up to 12 gpm flow rate (factory pre-charge 35 psi)
8" diameter x 12-1/2" height - 3/4" MIPT inlet
$39.93
4.75 Gallon Pressure Tank #A102 for over 12 gpm flow rate (factory pre-charge 35 psi)
11" diameter x 15" height - 3/4" MIPT inlet
$49.88
Adjustable Pressure Relief Valve - 3/4" inlet & outlet, brass construction (50-175 PSI) $46.79

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Related Items & Accessories:



Frequently Asked Questions

Q. "How how much can I expect my water pressure to fluctuate after I install the constant water pressure system?"
A. The Inline Constant Pressure System's constant output pressure should not fluctuate more than 1-2 PSI, even though the overall system's water flow requirement may change dramatically.

Q. "What is the incoming pressure requirement for these units?"
A. The constant pressure system requires a minimum incoming pressure of 3 PSI, while the inline boosting system needs only 1.5 PSI.

Q. "What is the water flow requirement for the constant pressure unit?"
A. The system operates on a wide range of flows from flooded suction to 35 GPM. The Inline System is not designed to draw/lift water from a source below the pumping unit. There is not an incoming flow requirement, other than the system needs to be supplied with a constant supply of water to keep the unit completely full of water at all times. It is recommended that the system be supplied with inlet line that is 3/4" in diameter or larger. Please note although the unit has no water flow requirement other than being kept full at all times, you still must meet the minimum water pressure requirement of 3 PSI.

Q. "What is the difference between water flow and water pressure?"
A. Water flow refers to the amount of water coming out of a hose, faucet or other pipe fixture in a certain amount of time. Water pressure refers to the amount of force that is put on the water to make it move from one place to another, or to the amount of force the water exerts when coming out of the pipe. Water flow is the result of pressure on volume. Volume is the amount of water available for delivery, and pressure is the force exerted on it. For example if you have a pressure of 3 PSI forcing water through a 1/2" i.d. pipe it will have a lower flow rate than that same 3 PSI forcing water through a larger pipe.

Q. "What does flooded suction mean?"
A. A "flooded suction" refers to a situation in where water flows to the pump inlet from an elevated source by means of gravity.

Q. "My water is sandy and somewhat abrasive. Can I still use these systems?"
A. Pumping abrasive or sandy water can damage any pump's internal components. We suggest installing a sand separator before the constant pressure or boosting system if you have these water conditions. We have many sand separators for you to choose from. Please note: If you are considering adding a sand separator before the constant water system you must make sure that your water system meets the minimum flow rate for the sand separator to function correctly.

Q. "Will I experience water hammer while using the constant pressure system?"
A. The pressure tank helps reduce water hammer by acting as a system buffer. However you may still need a water hammer arrester as water hammer is caused by a rapid shut off of a valve on a long run at the end of your plumbing system and the constant pressure system is installed at the beginning of your plumbing system.

Q. "What other items and/or tools will be needed to install the constant pressure system?"
A. The manufacturer recommends but does not include: wrenches, screwdriver, pipe sealant, pipe fittings, nipples, check valves, ball valves, unions and a 100 PSI pressure relief valve.

Q. "What size of a pressure tank will I need?"
A. For 12 gpm or greater flow, the minimum pressure tank size is 4 gallons; for 12 gpm or less, the minimum pressure tank size is 2 gallons. Oversizing the pressure tank is acceptable and will not adversely affect the system's performance or warranty.

Q. "What are the physical dimensions of the pressure tanks?"
A. The 2.1 gallon pressure tank has a diameter of 8" and a length of 12-12". The 4.75 gallon pressure tank has a diameter of 11" and a length of 15".

Q. "Can the pump run dry without any damage?"
A. No, never run the pump dry.

Q. "Will this system be able to handle other liquids besides water?"
A. Per the manufacturer, this pump has been evaluated for use with water only.

Q. "What does the optional 'Pressure Shut-off Sensor' do?"
A. The optional over pressure switch monitors the pressure levels within the constant pressure system. If the pressure level exceeds 100PSI, it will shut down the unit and allow your pressure relief valve to dissipate the excessive pressure.

Q. "What is NEMA 4 rating mean?"
A. The NEMA 4 rating means that the units enclosure provides a degree of protection from falling dirt, water, dust and sleet. The unit can be installed outdoors but the manufacturer recommends that the unit be shielded from direct sunlight to prevent overheating.



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