Efficient Plant October 2017 - 42

FOOD
&
BEVERAGE
processing
charge and suction pressures, ﬂuid information,

collar and repositioning it. Often, the assembly

the temperature," he explained. "If the tempera-

temperature, seal type, viscosity, speciﬁc gravity,

mistakes can be made at the manufacturing point.

ture is too high, this can cause certain seals to fail.

and power requirements.
Assembly error (always read instruc-

Improper assembly can also adversely affect

I insist on knowing the temperature. I've had calls

the testing results. "Any time there is a rotary

from people saying they were pumping beer at

tions): McCormick said that, even though

seal or mechanical seal, there is room for error

212 degrees and they can't understand why the

most pumps and seal kits come with detailed

in assembly," he said. "A mechanical seal can sit

seal is cracking. Well, if I had known that tempera-

installation and assembly instructions, improper

on a spring, and the pressure from that spring is

ture before I sold them the pump, I would have

assembly is a common mistake with sanitary

what pushes the rotating element up against the

known not to use that particular seal."

equipment.

stationary element. The stationary element could

"I don't know if it's that guy thing where guys

Knowing the required horsepower and speed

be a back plate made of stainless steel or it could

of rotation is also essential. "For example, you

just don't bother reading instructions," he said.

be another embedded silicon carbide or tungsten

cannot pump yogurt or ice cream or milk or beer

"And sometimes the operator or mechanic is very

carbide, or ceramic. All of these details make a

at high speeds because it will create foam or

experienced and knows what to do, but because

difference in how it is assembled."

damage the product integrity," McCormick ex-

he doesn't read the instructions, there is one small

Inaccurate or insufﬁcient information

plained. "In many cases, you need two speeds-

detail that gets overlooked. And small details can

(there can never be too much information):

one speed to pump the product and another for

make a big difference."

Not enough information-or the wrong informa-

CIP (clean in place) operations. You can't pump

tion-can mean certain failure, McCormick stated.

beer at 3,600 rpm because it will compromise the

"Sometimes I'm asked why is it important to know

end product. All of those little things have to be

McCormick explained that it could be a detail
such as loosening the set screws on the drive

MECHANICAL-SEAL FACES
Mechanical-seal choices have become increasingly popular in the pump industry, according to
Jim McCormick, SANI-PUMP Inc., Chattanooga,
TN. Many companies develop a set of pumpseal specifications to make it easier for their
customers to select one or more seals for an
application. The lack of a company specification
can cause problems with seal inventory, installation, and interchangeability. Many plants are
accepting seal components with unidentified
and/or inferior materials, making troubleshooting a nearly impossible task.
According to the American Seal and Packing
Co. (americansealandpacking.com, Santa Ana,
CA), a good company specification for pump
seals will include the following:
* seal materials with the widest range of
chemical compatibility
* seals that are easy to install
* seals that operate over a wide range of
temperature, pressure, and speed
* features that make seal repair

42 |

RELIABLE PUMPING SUPPLEMENT

easy and low cost
* seals that require the least amount of inventory and spare parts
* designs that allow the easiest conversion of
packed pumps to pump seals.
The most common seal-face materials:
* Carbon or carbon graphite. This is the old
standby, McCormick said. Carbon, or carbon
graphite, seals offer the greatest economy and lubricity for sealing non-abrasive
products. This is good for clean, abrasive-free
materials. It self-lubricates to reduce heat
and extend service life and works great with
all other seal materials.
* Ceramic. Generally, a 99.5% aluminum oxide
offers excellent wear characteristics due to
its hardness. It is chemically inert and can be
applied to nearly any product. In the sanitary
environment, ceramic offers the best resistance to sticky liquids, such as syrups. Ceram-

cracks or shatters. Like most other materials,
it wants to expand with heat, but it cannot.
Ceramic is much more resistant to abrasive
materials than carbon. It is also corrosion
resistant and inexpensive. Ceramic material is
most commonly paired with carbon.
* Silicon carbide. This is a bluish-black material
created by fusing silica and coke. It is in the
same family as ceramic (due to the silica),
but has much better lubrication qualities
and is harder. It contains no silicon that can
leach into the process and is excellent in an
oxidizing environment. Silicon carbide has
good thermal-shock resistance due to its
low thermal-expansion coefficient and high
thermal conductivity.
"In summary, silicon carbide's combination of
hardness, strength, and temperature resistance
gives it excellent capabilities for services in a
wide range of applications where high speeds,

ic cannot handle thermal shocks. It has zero
tolerance for thermal expansion and easily

high pressures, and chemical and abrasion resistance are required," McCormick said.

OCTOBER 2017

http://www.americansealandpacking.com

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