From: John De Armond
Subject: Re: Shurflo Water Pump Question
Date: Wed, 23 Feb 2000 18:16:25 EST
Newsgroups: rec.outdoors.rv-travel

Bob and Michelle wrote:
> 
> We have a Shurflo model 2088.
> 
> When we are dry camping the pump "cycles" periodically as if there were a
> leak in the line.  But, I can't find a leak anywhere.
> 
> When we are connected to shore water my fresh water tank fills up with fresh
> water.  I have replaced the water gasket on the fill valve and that did not
> stop the problem.  Then I tried turning the pump on even though I was
> connected to city water.  The tank stopped filling.  After leaving the water
> pump on for awhile, I can shut it off and the water will not continue to
> fill the fresh water tank.  I suspect the pump is allowing city water to
> backflow through it into the fresh water tank and is also allowing water to
> seep from the high pressure to low pressure system when I dry camp.
> 
> Has anyone else experienced this and is there a way for me to fix the
> problem without buying a new pump?


Yup.  The valves in the pump are leaking, allowing water to bleed
back through the pump.

Shurflo says that the valves can withstand city water water pressure
but my experience with several of these pumps says "don't bet on
it".

The solution is to put a check valve (Usually less than $5) on the
outlet line of the pump.  That's what I did on my system.  I found a
plastic check valve that would directly mate with the PEX fittings
used in my rig.  I found this valve at a mobile home parts store. 
Also probably available from an RV parts store but we don't have one
of those in town.

One thing you have to be careful of is to make sure the check valve
you select has a very low seat pressure.  If it takes more than a
few ounces per square inch to lift the check valve off its seat, the
pump won't be able to prime when dry.  The reason is the pump is
capable of pumping only a few ounces of air pressure.  If it can't
get rid of the air, it can't suck water up from the tank.  When I
first installed the check valve on my system, priming was iffy.  I
solved that problem by modifying the internal spring by cutting a
turn off it.  If you can hold the valve upright and rest a BIC
ballpoint pen on the plug shaft and the weight of the pen lifts the
plug off its seat, the tension is about right.

Someone else recommended rebuilding the pump with new valves.  That
will work for awhile.  But my experience using these same pumps on
my catering wagons says that the fix is short lived.  The valves
simply can't handle the pressure over a sustained period.  What is
especially hard on the pump valves is the pressure that results from
heating the water heater with the system under pressure.  The check
valve in the city water inlet and the check valve in the pump seals
off the water contained in the system.  As the water heater warms,
the water expands and the pressure rises until something gives or
the safety lifts.  Usually the plastic plumbing expands enough to
keep the water heater safety from lifting.  But the system is
subjected to 100 psi or more and this is very hard on the pump
valves.  An external check valve will take the pressure off the
pump's valves.

The real solution to this problem and to the problem of rapid
cycling is to install an accumulator.  ShurFlo makes an inexpensive
one, as does Jabsco.  I used a Home Depot small, 1 gallon well pump
accumulator that I just happened to have on hand. It's larger than
the Shurflo unit but since I had it laying around...  If you install
an accumulator, be sure to put a block valve on it, preferably a
ball valve.  The reason is that a small leak can leak for quite some
time without causing the pump to run.  With the accumulator
isolated, the pump will again cycle rapidly as yours is now, with
even a small leak.  Being able to hear the pump cycle is a handy
diagnostic tool.  The block valve is also nice when you're doing
other plumbing work on the RV.  Saves having to bleed the thing down
after each pressure test.  If you have a leak in whatever you're
working on and have to pressurize and depressurize the system
several times, it saves a lot of time not having to pump up the
accumulator each time.  Saves water too :_)

John