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At Bell & Gossett, we make
many different types of circulators. Some run at low
speeds and are lubricated with oil. Others run at higher speeds and are lubricated with
oil.
Others run at higher speeds and are lubricated by the
system water.
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| Some, like the Series 100, have a
coupler between the motor and the pump. Others, like our SLC Red Fox have a motor shaft
that’s directly connected to the pump. We
manufacture a very complete line of circulators, and one might look quite different from
another. But they all do essentially the same thing.
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| Job
Description A circulator’s job is to
move hot water from the boiler to the radiators, and then return the cooled water for
another injection of heat. In other words, it creates a flow on which heat rides like a
passenger.
Ever think about how it gets that job done? A lot of
installers think the circulator’s job is to lift the water to the top of the system.
It’s not. That job has already been filled by the feed valve. |
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And since the system
is already completely filled with water, all the circulator has to do is move it around.
It helps to think of a heating system as a Ferris wheel.When a Ferris wheel turns, the
weight going up balances the weight coming down. There’s no lifting going on here,
there’s only turning. That’s because everything is in perfect balance. The
Ferris wheel’s motor doesn’t have to do any lifting. All it has to do is
overcome the friction in the bearings (and in the air, of course) to set the big wheel in
motion.
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Now think of a heating system. It’s like a big wheel of water, isn’t it? Once
the feed valve has done its work, there’s no lifting involved. The system is
completely filled with water. So when the circulator comes on, the weight of the water
flowing up is going to be perfectly balanced by the weight of the water flowing down. And like the motor on a Ferris wheel, all the circulator has to do
is overcome the friction to set that "wheel of water" in motion. In this case,
the friction is caused by the water as it rubs against the inside of the pipe and goes
through valves, fittings and other system components. We call this friction "Pressure
Drop". If the circulator can overcome the system’s pressure drop, water will
flow.
"Pump head" is not height
We use the term "Pump Head" to describe the force
the circulator develops to overcome pressure drop. When we work with closed hot water
heating systems, "Pump Head" has nothing to do with the height of the building.
It has only to do with the circulator’s ability to overcome friction. That’s
because the system is completely filled with water. Height, as far as the circulator is
concerned, doesn’t exist. The circulator doesn’t know (or care!) if the building
is 100 feet high and ten feet wide, or ten feet high and 100 feet wide. All it knows is
friction.
Another thing you have to understand is that the force the
circulator creates, the Pump Head pressure, has nothing to do with the static pressure
created by the column of water in the building.
Pump pressure and static pressure
Remember we talked about static pressure when we looked at
feed valves? Well, the pressure created by a circulator and the pressure created by the
feed valve are totally independent of each other.
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Static pressure has nothing to do with the number of
fittings and valves or the width of the building’s piping network. Static pressure
has only to do with gravity, and the weight of the column of water.
"Pump Head," on the other hand, has a lot to do
with the number of fittings or valves and the size of the building’s piping network.
But it has nothing to do with gravity or the fill pressure of the system.
Take a moment now to let that sink in. Get it straight in
your mind, because it’s one of the most often confused points in hot water heating.
Static pressure and pump pressure are totally independent forces. You can add them
together, but they’re created by two different things. Don’t mix them up.
| How circulators work in closed systems Okay, now let’s take a look inside the business end of a
circulator and see if we can figure out how it manages to create this force that’s
capable of turning this big water wheel we call a heating system.
The circulator, like the rest of the closed heating system,
is always filled with water. There’s no way it can ever empty itself of water when
it’s running. All it can hope to do is toss out what’s currently inside of
itself.
But as soon as it tosses that water out, more water comes
flowing in. It’s operating in a sealed loop, so the supply of water is unlimited.
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| The rotating part of the
circulator is a water wheel we call an "impeller." An impeller uses centrifugal
force to create velocity and move water. The pump shaft passes through the dead center of
the impeller’s back end and comes out in front through an opening that’s know as
the "eye." The "eye" of an impeller is similar to the "eye"
of a hurricane. Everything swirls away from that central "eye" because of
centrifugal force.
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The circulator’s impeller
has curved vanes that direct the water flow. These
vanes fling the centrifugally forced water away from the impeller’s eye toward the
smooth channel of the pump’s body. We call that pump body a "volute"
because of its unique shape.
The volute’s smooth channel accepts the water from the
impeller and directs it toward the outlet of the circulator.
But before the water can leave the circulator, it has to
pass through an exit channel that’s significantly smaller than the entrance channel. |
| The water has to
squeeze through this smaller opening to get out of the volute. The effect you get is
similar to what happens when you put your thumb over the end of a garden hose.
The velocity increases, doesn’t it? Well, that
velocity is the force that moves the water around the system’s pressure
drop.Remember, there’s no lifting going on here, nor pulling or pushing either.
Circulators turn the water, just like a big Ferris wheel.
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| Series 100
The Series 100 circulator has a bearing assembly that holds
the pump shaft. The shaft spins at 1,750 rpm on two, quiet-operating sleeve bearings.
Don’t use detergent oil because detergent builds up over time, and since it has no
lubricating properties, it can lead to bearing failure.
The mechanical seal in the Series 100 is made from carbon
and a special alumina-oxide ceramic. We use this ceramic because it can take a wider range
of pH than the common ceramics used in some pump seals. Ideally, the system water should
have a pH no lower than 7 and no higher than 9. Depending on the quality of the water and
the type of chemicals used in the system, however, the pH can change. This is a commonly
overlooked problem that often leads to system corrosion problems and circulator seal
failure. We’ve engineered our seal to last under these variable conditions, but it
pays to check the water’s pH when you’re troubleshooting a system.
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| We use a wool
ticking to draw oil up onto the sleeve bearings. The capillary action of the wool brings
the oil to the bearing and leaves any sediment behind in the reservoir. If you over-oil the bearing assembly, the excess oil will simply
overflow through the bearing assembly’s weep-hole.
The weep-hole is important, and you should never plug it.
If you do, any dirt or sediment in the oil will find its way into the bearings and shorten
their life.
We make our own motors for the Series 100. We use a thick
shaft, heavy rotor and over-sized, dirt-resistant switches for long life. They, too, have
sleeve bearings so they’re also very quiet. We cradle our motors in oil-resistant
motor mounts to make sure the slight purr of the motor doesn’t make its way into the
system piping.
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We stamp our couplers out of steel for good balance and quiet operation, and we dip the
ends in a special epoxy to lessen the possibility of wear between the coupler’s yoke
and springs.
Those are just a few of the features that continue to make the Series 100 one of the most
popular circulators in America.Be aware of water temperature when you’re
installing any circulator. The Series 100 operates well in water that’s less than 225
degrees F. The SLC can withstand water that doesn’t exceed 230 degrees F. You
won’t normally find water this hot in a hydronic system, but it can become a problem
if you’re using the circulator to pump water out of a steam boiler for a hot water
zone. |
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Morton Grove
Tel 847 966-3700
The Circulator, And How It Moves Water