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ShurFlo Extreme Smart Sensor 5.7
Water Pump
Installation and Tech Notes


Shurflo water pump


For years the typical RV came with a basic water pump that would pump up pressure and shut off. When the pressure dropped, the pump would kick in and pump up the water pressure until it reached it's limit, at which time it would cut out again. This style of water pump is a "demand" pump, because it kicks in whenever water is demanded. It's a fixed displacement piston pump so it will always put out the same constant volume of water flow. When the water needs are minimal, such as a trickling faucet, the pump will cycle on and off as the pressure increases and drops. This hammering action can be minimized by installing an accumulator tank, which is a large surge tank capable of buffering the water pressure, like a big water balloon that expands as needed, to smooth out the pump cycling.

The most recent development has been the variable flow water pump. The pump that started this all was the ShurFlo Extreme Smart Sensor 5.7 water pump (I know, it's a long name, but I didn't choose it so don't blame me), and it is still the most popular water pump out when upgrading. Made by the ShurFlo Corporation, this pump is different in that it has a variable displacement. Instead of pumping at a fixed speed, this pump will vary it's water volume to suit the water demand. The Smart Sensor portion refers to a sensor that does more than just look for pressure drop. It's a variable speed sensor that will control the pump motor's speed according to how much the pressure drops. If you only need a trickle of water, the pump will run at low rpm to keep the volume flowing and not let the pump cycle on and off. When you really need lots of water the pump will put out up to 5.7 GPM, which is substantially more than the typical 3 GPM of a basic water pump. This will ensure that you get plenty of water when you need it. This design also does not require the accumulator tank because it doesn't have the harsh on-off cycling of a typical piston pump. It is capable of extremely quiet operation if the installation guidelines are followed.

Installation Tips:

This pump installs in similar fashion to your basic water pump but, because it has a high output rating there are a few unique things that need to be followed when installing this pump.

First of all, you cannot use a standard water pump strainer with this pump. They are too small. You will need the larger high flow strainer that is made for this pump to keep it from starving due to lack of water flow.

Secondly, if you mount this unit solidly to the compartment wall or floor it will transmit harmonic vibrations throughout the coach and it'll sound just like your basic water pump, probably even louder because it's bigger. The pump has four mounting feet with rubber bushings in them. Do not over tighten the mounting screws or else those vibrations will be transmitted to the coach. Leave the screws out far enough that the rubber is not compressed. Also, many RVs will benefit from adding a vibration absorbent material as a mounting pad between the pump and mounting surface. Let's face it, mounting it to a sheet metal panel will act as a sound amplifier. Using a thick piece of rubber belting or even acoustic plywood will make a big difference.

Thirdly, and also related to vibrations, is the fact that this pump spits out a lot of water. When that water expands under pressure into the water lines, it's going to make some noise. ShurFlo recommends using the flexible hoses that they have available to isolate the pump from the hard poly water lines. I'd recommend doing this on the inlet as well as outlet sides and make them at least 18" long. Also, if the water slams into a 90 degree ell bend right away it will make noise. Try to send it straight into the water line and minimize the bends as much as possible. It's better to use the gradual bend of the flexible hoses to redirect the connections.

Service Notes:

If you are having a lack of water volume, check to see if your pump is sucking air. Are all the hoses tight? Is the strainer bowl on tight? Is the water level covering the fresh water tank's pickup port or is the coach out of level and you are sucking air. Finally, the input and output fittings of the pump are simply pushed into place and held in with plastic C lock retainers. These fittings have rubber O rings on them and these O rings need to be coated with grease. A special plumber's grease, commonly used for faucet valve stem lubrication is designed for use with potable water. If there's not enough grease you can suck air past the O rings, causing the pump to cavitate.

If the water flow from the faucet is erratic and surges and falls you may have an issue with the sensor. If the sensor's tolerances are set too tight it'll prematurely kick in and out. Before condemning the water pump try to adjust the sensor. On the pump head there is a small screw right in the center. If you turn it between 1/2 to 1 full turn clockwise you will reduce the backpressure and the surging should stop. Be careful not to crank away too much. Take it in short 1/4 turn increments and then test before going farther.


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Submitted by Mark Quasius - 10/03/06

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