So
the cost of boating just keeps going higher and higher
(belying the notion that there's no inflation) and you're
tired of paying those ridiculous yard bills? But you're
not a do-it-yourselfer type and the idea of attempting
to repair a pump lies somewhere between computer programming
and neurosurgery?
Well, I'm going to show you how easy
it is, and how the worst part of the job is getting
the pump out of that deep hole so you can work on it.
But here's something else you'll be interested to know.
All three of the pumps used for this demonstration were
pulled out of dumpsters at boat yards. And all three
were repaired at a cost of nothing more than my time.
Not one single new part was used! And it took a grand
total of one hour and seventeen minutes to repair all
three. So if you're getting the idea here that the former
owner of these parts maybe got ripped off, maybe you're
right.
Our first example is a Jabsco mascerator
pump. Now, I'm not going to blame anyone for not wanting
to repair one of these, so bear in mind that we're just
using it as an example, for it's basic style is common
to a lot of pumps. For pumping fluids, it use a positive
displacement neoprene impeller of the sort that is considered
self-priming. This resides on the inner side of the
pump body, while on the outside is a simple three-pronged
device that , well.......you know, mascerates the ugly
stuff.
So what went wrong with this pump?
The same thing that happens with nearly all of them
that go bad. The pump was mounted in a location where
the motor got wet. There wasn't anything wrong with
the pump body. When you look at a pump motor, and it
looks like what you see in the photo at left, then you
can be pretty sure that water damage to the motor is
involved.
So the first thing we do is take it
apart. We start by pulling the nuts off the end plates.
Note that the two parts are held together by two sets
of long rods. When you do this, it's a good idea to
take a piece of paper and sketch out the orientation
of the two parts so that you won't have to experiment
with how it goes back together, thereby wasting time.
Having done that, we go ahead and pull apart the motor
from the pump body, being very careful not to damage
the paper-like gaskets. Beware, they tear easily, so
treat them gently or you'll be heading out to buy replacements.
 At
left is an exploded view of the pump housing being disassembled.
At the end of the shaft we have the three-pronged mascerator.
To get it off, we gently tap the base of one of the
blades with a hammer in a counter clockwise direction.
It should then spin right off.
Inspect the impeller and pump housing
for damage. Light scoring of the housing is tolerable
while heavy scoring or wear is not. Check the impeller
for damaged blades. If so, replacements are always available.
In this case, it's a plastic housing so that if running
dry and overheating was involved, the plastic casing
may have distorted. Check to see that the stainless
cover plates fit flush. If not, it's going to leak.
Next we contemplate pulling the end
plates off the motor housing. While this is easy enough
to do, the hard part is getting it back together in
the same order that it was assembled. Below you have
a view of the parts. Again, take your piece of paper
and sketch out which parts go where, particularly all
the little washers and seals that go on the pump end
of the shaft. Having done that, go ahead and pull the
thing apart.
In the photo below you see the brushes
that reside on a little plate that fits into notches
in the motor body. The brushes will want to fly out
so that the little springs get lost. Don't let this
happen.
| The
brush holder plate removed. Notice how it fits
into the slots in the motor housing. The springs
push the brushes outward when it is removed. |
 |
Having gotten the motor apart, we want
to see what the problem is. In this case, water got
in and caused corrosion. Whether or not the the motor
can be repaired is going to depend on how badly it's
corroded. The armature is the large rotating part in
the center with all the copper windings around it. If
this is very badly corroded, then the pump motor should
be replaced. In this case, the corrosion was just
enough to cause the motor to hang, so all that needed
to be done was clean it up and put it back together.
In other cases, pumps may go bad due
to the motors or pump housings burning up. In this case,
you should see some obvious heat damage, but be sure
to look closely. Pump bodies that have run dry may be
scored and have to be replaced. In other cases, it may
just need a new impeller. If the motor is burned, then
it needs to be replaced. In most cases, both motors
and pump bodies are separately replaceable, saving you
the cost of buying a whole new pump. The motor for this
pump could be had for as little as $30.
To clean it up you need a piece of
bronze wool or a brass (preferred) or steel wire brush
the size of a tooth brush. Using this, clean all the
rust off the motor housing, the armature and end plates,
being careful not to damage the lacquer like insulation
on the windings. The end plates are aluminum and all
the corrosion needs to be cleaned off on the ringed
grooves that fit into the motor housing so that end
plates will align properly, and not become out of alignment
because of corrosion buildup. Scrape with the corner
of a flat screwdriver blade if necessary.
The stator consists of the two large
magnets inside the motor housing. If there is corrosion
on these, take your bronze wool or brush (CAUTION:
do not use steel wool!!! The steel fragments will adhere
to the magnets and ruin the motor.) and clean any corrosion
off the motor shaft. Now put a single drop of oil on
the shaft in way of the end bearings and spread it over
the shaft. Put some on those rusty end end plate threaded
rods too.
The brushes need to be checked for
wear and burning. You can see from the photo above how
long they are when nearly new. If they're down to the
nubs, then they're worn out, at which point you can
opt to replace the motor or attempt to get replacements.
Keep in mind that to replace them, you'll have to solder
the wire connections on to the wire terminal points
on the holder.
 |
Dismantled
view of motor. The circled area denotes area of
heavy corrosion that was inhibiting the motor
rotation. Once cleaned up, the motor ran freely.
When taking
apart, be sure to make note of which way all
the parts are oriented. It won't work too well
if you put it together backwards. |
Now you're ready to put the pump back
together, and here's where the tricky part begins --
how to inset the commutator into the brushes without
parts flying all over the place because they're spring
loaded. The trick is to use pieces of masking tape to
wrap the brushes and hold them in place. You need a
length more than enough to wrap a complete revolution
so that the tape sticks back on itself, but without
sticking the tape to the brush holders. Bear in mind
that the tape has to come off once it's partially assembled.
Also put your tape overlap on the OUTSIDE of the holder
plate.
Insert the rotor into the housing.
Now gentle place the brush holder plate so that the
brushes fit over the commutator and snap the plate into
the slots on the motor housing. Tweezers work best for
pulling the tape off the brushes, but you have to be
sure to get all of it out. After this, you place the
opposite end plate on the shaft and back into position,
aligning the long bolt holes so that they're the same
on both sides. Some motors will have positioning slots
while others don't.
As you try to feed the two long bolts
through their holes, the magnets are going to be giving
you trouble as they pull the bolts off course, refusing
to allow them to go into those tiny little holes. There's
only one solution for this problem -- PATIENCE. Just
keep playing with them and you'll eventually get them
in the holes at the other end. Once you've got one,
put the nut on it quickly so it doesn't fall back out.
Putting the pump end back together
is fairly simple, but you do have to be sure to get
the gaskets, cover plate and end body in the proper
alignment or the pump won't work. Be sure that the orifice
notches are all aligned the same way, and that you've
got the rubber ring and metal washer in the right order.
You did make that sketch, didn't you? If not, now you
know why this was recommended.
Before final assembly, coat the gasket
surfaces on all sides with a thin layer of silicone
gasket cement. Within the neoprene impellor pump body,
its very important that the layer of gasket cement not
be so much that it's going to squeeze out into the pump
body where it may interfere with the impeller. The edge
of the pump body is less than 1/8", so I usually
use a very small screwdriver blade to spread the cement
around in very small amounts, and quite thinly. Just
enough to make a good contact with the USED paper gaskets.
Notice now the order in which the various
parts go together. The bronze impeller goes on last,
while the neoprene impeller goes on the shaft first.
It's best to do a dry assembly first, before you apply
the gasket cement, just to make sure you got it right.
Once you do, you're ready to button the whole thing
back up. In torqing the nuts you use about 15 lbs pressure,
which is hard to measure if you don't know what 15 lbs
of hand pressure is. In any case, it's neither light
nor very hard, but somewhere in between.
When I do these rebuilds I usually
have a spare 12 volt battery nearby for testing. You
can take the pump to your car or boat battery
and simply put the wire ends against the terminals to
briefly test it before reinstalling. With a gas powered
boat, be sure there are no fumes in the bilge before
doing this. You're nose should tell you.
Summary
The same basic methods can be used
to repair any type of rotary vane pump. Once you've
done one, you'll feel a lot more confident approaching
the next one. Whether it's crapped out due to
water damage or buggered impellers, these pumps are
frequently repairable. Pumps that have overheating damage
due to running dry or excessively long are not.
These days most products have a way
of becoming obsolete almost overnight. Not so for marine
pumps. Many of these things have been in production
for decades. Do-it-yourselfers almost never throw old
pumps away. If you replace a pump, you save the old
one and repair it, keeping it around as a back up. For
the current boat or the next. Over time, you can save
a heck of a lot of time this way.
See companion article Repairing
Diaphragm Pumps
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