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This
is our follow up to the
Repairing Rotary Vane Pumps. The repair of
diaphragm pumps is no more difficult than other
types. In fact, it's usually a bit easier.
There are two basic style pumps
found in common use that look very different,
but utilize the same principle of a series of
alternating diaphragms. These are the PAR (acronym
for the original designers, Peters and Russell)
and that represented by the Shurflo type pump
shown below, which is a fresh water system pump.
The PAR type pump also comes in bilge pump models.
Solve the Cause of Failure
First
People are always complaining
about the unreliability of these pumps due to
their history of frequent breakdowns. In fact,
these pumps are reliable when installed properly,
but frequently they are not. There are three main
problems that usually cause their demise.
1. They are located in
a place that gets wet.
2. Diaphragm pumps are
intolerant of any kind of debris in the water
being pumped.
3. Freezing as a result
of inadequate winter layup.
The first problem should speak
for itself; all pumps are electrical apparatus
that should be located in a clean, dry area. Note
that just replacing a water damaged pump isn't
going to solve the problem. You need to eliminate
the reason why it got wet.
The second problem is one that
can be solved by installing the appropriate sized
strainer or filter so as to prevent debris from
getting into the inner workings of the pump. By
far -- as in the case of the example below --
the primary mode of failure of water pressure
pumps comes from aluminum water tanks. Aluminum
tanks will build up very heavy corrosion deposits
on the inside of the tank. These deposits look
like very little stones, and it is these that
get into the diaphragm valves and cause their
malfunction.
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| The
Shurflo pump |
In the case of this Shurflo pump,
when we took it apart, the diaphragm assemblies
looked like they were clogged with fine gravel.
This is what prevented the pump from working.
In fact, this pump did have a strainer in the
line between pump and tank. Unfortunately, the
strainer mesh was so coarse that it permitted
these finer particles to pass through it. Therefore,
the solution for use with aluminum tanks is to
use a very fine mesh strainer and this sort of
thing will be prevented.
Repairing the Pump For
the Shurflo pump, the hardest part of repairing
it is getting it back together after taking it
apart. It's somewhat like taking your watch apart,
although not quite that bad.
When you remove all the screws
from the outer housing and pull it apart, there
is a U-shaped lever that is operated by a diaphragm.
It is tensioned so that when you pull the outer
housing off, it will want to fly away. Remove
the cover VERY SLOWLY, and once it is off, take
note of the position of this U-shaped lever. Write
it down on a sheet of paper so you don't forget,
because if you do, you'll have a hard time getting
it back together, for its positioning will not
be clear to you. This is the lever that is part
of the pressure switch that turns the pump off,
so it's important to get it right.
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| The
main components. Notice also that
this motor got wet, but not enough
to damage it. |
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Okay, that's the hard part and
everything after this is (or should be) easy.
As you can see in the photos here, there are actually
two problems with this pump. Not only is it clogged
with debris, but the motor got some water into
it. We cleaned up the corrosion and the bearings
the same as outlined in the Repairing Rotary Vane
Pumps. Putting it back together, we tested it
on a battery and proved that the motor was working
fine.
Next, onto the pump itself. This
was real easy. Pulling out the remaining screws,
the diaphragm assembly comes apart and goes back
together easily. Here the debris of aluminum oxide
particles is plainly apparent. All we had to do
was to use an ice pick or awl and pry the little
particles out of the grilles in the diaphragm
housings. We then check the various parts for
wear or damage. There being none, we then ready
to put it back together.
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| The
culprit: Aluminum oxide from an
aluminum water tank clog the diaphragm
valves. The repair simply requires
removing this debris. |
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So what if there is damage or wear?
Not to fret, replacement parts are available for
nearly all popular brand pumps. From your nearest
boating center? Uhm, no. Esoteric parts like this
are usually only available from marine parts distributors
or suppliers. Fortunately, such parts are now becoming
widely available to consumers through distributors,
many of which can be found online. Large distributorships
carry a huge array of replacement pump parts.
Another thing we should point out
is that replacement motors are also now available
at reasonable prices. We're talking like $30-$40
rather than the $90-$100 prices of ten years ago.
This can definitely make the repair of a $150 pump
worthwhile, yet alone a $300 pump.
When putting the pump back together,
be sure to torque all the screws snugly. Then go
back and make sure that each screw has the same
approximate torque on it so that the more delicate
plastic housings don't get distorted by uneven torque.
That's all there is to it.
PAR pumps, although they look very
different, really operate much the same. In this
case, the motor uses a drive belt from the motor
to actuate a cam that actuates the diaphragms. With
this pump, there's no difficulty at all taking it
apart, for the manner in which it is assembled is
very clear.
The diaphragms in this pump are
prone to wearing out, as well as being damaged by
debris. Here you need to look each of the removable
diaphragms over and check the neoprene parts for
cuts, splits or damage. The damaged ones need to
be replaced. If the pump is old, it's best to order
and replace the complete set of four. And get a
couple of spare drive belts while you're at it.
If you don't have a strainer on
the intake line, it's time to install one. And be
sure to get one with a fine, not coarse mesh.
Finally, if you are using a dockside
water pressure connection, be aware that if the
reducer regulator or the check valve in the system
aren't functioning properly, this will cause the
pump to be subjected to high pressure. This can
damage the diaphragms. So, if you are having a chronic
problem with pumps failing frequently, you should
check to see that these two devices are functioning
properly.
One way you tell for sure that
the check valve is not functioning (or there is
no check valve or reducer valve in the system) is
when the hoses connecting to the water pump are
ballooning out from excessive pressure. If you have
ballooning water hoses, you got a problem that needs
to be corrected immediately.
Companion article: Repairing
Rotary Vane Pumps.
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