Keeping the Pressure On

Among the many things that differentiate life in a motorhome from a fixed residence, the
plumbing system is an area that can require the greatest adjustment to living style.
Inconsistent water flow and pressure and the pulsing hum of the water pump as it cycles on
and off are problems that most motorhome owners have just learned to live with, but they
won’t have to anymore. After much anticipation, SHURflo has finally released its new
Extreme Series Smart Sensor 5.7 pump, designed specifically for those motorhome owners who
want “just like home” water flow and pressure, along with quieter operation. As you might
imagine, this was no small feat; it required a completely new pump design to achieve the
goals SHURflo’s customers had requested. Since the first objective was improved water flow
and pressure, the Smart Sensor was designed around a new one-piece, five-chamber diaphragm
with umbrella valves and larger valve passages. In addition to maximizing water flow and
reducing the likelihood of valve fouling due to debris in the water system, the umbrella
valve design provides a superior seal, acts as a check valve and holds stable water
pressure, according to SHURflo. Both the inlet and outlet ports measure 1/2 inch, and are
sealed by double O-rings to ensure against leaks. These features contribute to a flow
rating of 5.3 gallons per minute (gpm) at 12 volts DC, but it will operate at 5.7 gpm at
13.6 volts (as when the AC generator is running or the coach is plugged into shore power).
Shut-off pressure at 65 psi was chosen because it delivered SHURflo’s performance
requirements without overtaxing motorhome plumbing systems (the Recreation Vehicle Industry
Association currently requires motorhome manufacturers to test their plumbing systems to 80
psi). The typical motorhome water-pump motor runs at one speed and uses a pressure switch
to cycle the motor on and off, based on water demand. This design gets the job done, but it
creates unwanted noise and fluctuating water pressure. The Smart Sensor 5.7, on the other
hand, utilizes a pressure sensor that works in concert with a microprocessor housed in the
baseplate. The sensor measures the water pressure in the plumbing system, and then sends an
electronic signal to the microprocessor, telling it to speed up or slow down to match
demand. This design eliminates the need for a pressure switch or an accumulator tank, and
there is absolutely no cycling. In addition to the variable speed feature, the
microprocessor also manages other features to ensure reliable operation. For example, if
you’re dry camping and your battery power drops below 12 volts, the microprocessor will
recognize the reduced voltage and will turn the pump off at a lower pressure to prevent
stalling. If you’re running low on water and the pick-up becomes uncovered, the unit’s
thermo protector feature will step in to turn the pump off before it gets too hot. And
finally, 10-amp limiting prevents the unit from ever drawing more than 10 amps, thus
increasing battery life. SHURflo also took a number of steps to make sure that the Smart
Sensor 5.7 will last for years of fulltime use. Since corrosion is the No. 1 cause of
pumpmotor failure, the motor is housed in a seamless steel shell with O-ringed end bells.
There are no screws or holes in the shell, and even the motor wire is sealed by an
overmolded rubber grommet — all in an effort to keep moisture out of the motor assembly.
The microprocessor and circuit-board assembly are housed outside of the motor shell, and
are potted to prevent corrosion and protect the electronics from damage due to road
vibration. Finally, a heat sink dissipates heat from the electrical components. SHURflo
claims that the Smart Sensor 5.7 not only produces residential-style flow, but it can do so
when more than one fixture is in operation. As we’re sure you’re familiar, whenever you’re
in the shower and your significant other opens a faucet in the kitchen or bath, water
pressure can drop significantly. The Smart Sensor 5.7’s increased flow capacity is designed
to overcome the drop in pressure, maintaining satisfactory flow at both fixtures. To test
this claim, we visited SHURflo’s sprawling facility in Cypress, California, to have the
Smart Sensor 5.7 installed on a 1999 Holiday Rambler Endeavor and test its capabilities.
The coach originally came equipped with a SHURflo classic pump, a smaller unit that is
commonly found in motorhomes and trailers. Before commencing installation of the Smart
Sensor 5.7, we wanted to test the original water pump’s performance, so we could draw a
direct flow comparison. First, we turned on the shower in the Endeavor’s bath and observed
normal water flow. Then the bathroom faucet was turned on, at which point we witnessed an
approximate 30 percent drop in water pressure at the showerhead. When the kitchen faucet
was opened, that deficit was increased to roughly 50 percent. When replacing the original
pump with a Smart Sensor 5.7, the most important consideration you must keep in mind is
that the new pump is quite a bit larger, measuring 5.43 inches from foot pads to top and 5
inches wide. As long as space permits, the rest of the installation will be a breeze. The
only other installation tips SHURflo suggests is using flexible 1/2-inch hose into and out
of the pump for unrestricted flow and an Extreme Series High-Flow strainer on the pump’s
inlet side to prevent debris from entering the pump. Use of the flexible hose also helps
avoid transmitting pump vibrations directly to the motorhome plumbing. The original pump on
the Endeavor was mounted on the back wall of a lower storage compartment made of
polyethylene plastic. SHURflo engineers commented that the plastic resonates pump-motor
sound like a snare drum and, for best results, should be isolated as much as possible. A
3/4-inch-thick piece of plywood was cut to fit into the compartment floor and screwed into
place, and the Smart Sensor 5.7 mounted to it. Back inside the coach, we once again turned
on the shower and observed what appeared to be normal flow, except this time the pressure
felt greater and there was absolutely no pump sound. When the bathroom faucet was opened,
flow dropped approximately 5 percent, and perhaps another 15 percent when the third faucet
was opened. Clearly, the Smart Sensor 5.7 worked as claimed. If having “like home” water
flow in your coach is something you’ve always wanted, the SHURflo 5.7 will fit the bill.
With a three-year warranty and a suggested retail price of $209.99, it is well worth the
investment. SHURflo Pump Manufacturing Company, (800) 854-3218,


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