SUBJECT: Communicating with suppliers
The precise meaning of words continues to be the major obstacle
when technically trained people try to communicate with non-technical
people, and the sales representatives of outside vendors.
Sometimes the results are funny:
I have worked with overseas translators for more than twenty five
years and have had "hydraulic ram" translated as "wet sheep" and one
time when I told my students that "failure of this course would
require attendance at a make up school", it was translated as a
school where you would be taught how to put on face powder, lipstick,
eye shadow. etc.
The problem is not limited to international dialogue, it occurs
frequently between people using a so called common language. The
result can be frayed nerves, extra cost, unexpected down time and
costly failure. Here are a couple of examples of what I am talking
about. Do you do this?
The word "documentation" has multiple meanings and is often
confused with "material identification". There is a major
- Do you need material traceability? Nuclear people often
require this. The material has to be traced from the original mill
(melt and batch numbers) through manufacture and supplier to the
end customer. It 's a costly procedure to provide all of the paper
work to document all of this
- Maybe you need only the "physicals". Things such as grade,
tensile strength, coefficient of expansion, etc. This information
is usually readily available and should not add to the cost of the
- Perhaps you need only a list of the ingredients. If you are
purchasing stainless steel maybe you need only the percentage of
chrome, nickel, sulfur, etc.
- Tolerances can be tricky. If you don't need a tight tolerance,
don't ask for it. Tight tolerances always come at a high price
because they require extra machining steps There is a big
difference between ± 0.001" and ± 0.0001".
People that deal with elements such as carbon or ceramic often
keep their process and tolerances a secret. They should not be
reluctant to supply the "physicals", but seldom will discuss their
manufacturing techniques. It is these techniques that give them their
The product must meet a specification
- Is the specification for materials or design, there is a major
difference! Many times there is no specification, but the engineer
assumes there is one and asks for it any way. Questions like,
"Does this seal have FDA. (Food and Drug Administration) approval?
There are no FDA approved seal designs, and in most cases the
materials are not specified.
- Some specifications are real. Meeting the API
specification dictates a special mechanical seal gland that
incorporates certain features and tolerances, along with fitting
sizes. Do you really need that specification, or do you want the
seal gland to perform the function? If you are working in the
petroleum industry you will need a gland that meets the API
specification, but outside of the petroleum industry you need only
a gland that performs the function which is available at a much
lower cost, and will fit process pumps without a costly
- The ANSI, ISO, and DIN centrifugal pump specifications
describe a pump with an impeller located too far from the
bearings. If you want reliable mechanical seal performance you
will not want a pump built to any of these standards, you will
have to purchase a more expensive "heavy duty" design.
The only way to solve the problem with specifications is to give
the supplier a copy of the specification you want him to meet
whenever you buy what ever it is you're going to purchase. Don't ask
him to meet the specification, give a copy of the specifications to
You have special knowledge about the fluids you are going to seal
that is not generally known outside of the industry. This lack of
knowledge on the part of the supplier can result in a premature
failure with all of its associated problems and costs.
- Ask a mechanical seal supplier to recommend an O-ring for the
dye used in the textile industry and he will recommend Viton®.
What he doesn't know is that a caustic "boil out" is common in the
process, and Viton® will be destroyed during the "boil out"
phase. Unfortunately the failure will occur five to ten days after
the "boil out" so the connection between "cause and effect" is not
- Kaoline is a product used in the paper and a few other
industries. Does your seal supplier know that Kaoline is a very
unique product that has abrasive solid particles less than one
micron in size, that will penetrate between lapped seal faces and
damage the sealing surfaces?
- Do you commonly clean or flush the process lines with caustic,
steam or some other type of cleaner? The O-ring that your supplier
will be choosing must be chemically compatible with this cleaner
as well as the product you will be sealing.
- The paper industry also uses chemicals called black liquor,
green liquor and white liquor. Depending upon the process these
products could be either acidic or caustic. If your seal supplier
makes the wrong choice you will have a seal failure within two
weeks when the elastomer swells up and locks the seal. A more
serious problem can occur if Reaction Bonded Silicone Carbide was
chosen as a hard face. This material can break down in high pH
- Buying a new pump? What data did you give the supplier. Did
you give him a print? The head and capacity? Maybe you just gave
him the size of the old pump, or a diagram of the piping layout.
Are any of these good enough?
- The piping is often different than that shown on the print.
When lines are added the print is seldom changed.
- Did you supply a real system curve or just a simple single
- Are you sure the existing pump is the correct size? If
there is a mechanical seal installed you know the seal is
experiencing premature failure (the sacrificial carbon is not
wearing out). Maybe the shaft is deflecting because the pump is
running off of its B.E.P. or cavitating. Most existing pumps
were supplied oversized to compensate for the safety margins
that were added by the people making the original calculations
Do you work in the marine industry? That industry is a lot
different than the process industry.
- Alignment between the pump and driver is different because the
ship's hull flexes. Off shore platforms do the same thing making
most alignment techniques ineffective.
- Salt water is a unique combination of high chlorides and low
pH (8 to 9). This is a deadly combination for "crevice corrosion"
of any metal that passivated by forming a protective oxide layer
(ceramic) on the surface of the metal. Stainless steel, alloy 20
and titanium are a couple of examples of such metals. The
corrosion takes place between close fitting parts and especially
under O-rings and clamped gaskets unless these parts are
lubricated with zinc oxide or a similar sacrificial anode
material. Does your supplier understand this, or will he supply
you with a standard O-ring lubricant and six months later you have
There is something unique about your plant or operation.
- High levels of Ozone will attack Buna N rubber compounds.
These rubber materials are commonly used in the popular rubber
bellows seal designs (Crane #1, #2 or #21). Some facilities have
high levels of ozone in the shop atmosphere and the seal supplier
might not know it.
- You may be using a special O-ring lubricant that is compatible
with your product, but not the elastomer in the mechanical seal,
valve, gauge, etc. If you are using anything other than silicone
grease this could be a problem, so check with your supplier. As an
example&emdash;petroleum products cannot be used on EPR O-rings.
If you make this error the failure will usually occur within ten
to fourteen days.
- Does your mixer alternate between pressure and vacuum? A
conventional balanced seal is balanced in only one direction. You
may need a two way balanced design. Many split seals also have a
problem with alternating pressure direction.
My many years in this business has taught me that you only get the
right answers when you ask the right questions. Recognize that most
of us don't know the right questions, so be sure you volunteer your
inside information to save both yourself and the vendor the obvious
problems that arise from his lack of knowledge about your product or
® DuPont Dow elastomer
For information about my CD
with over 600 Seal & Pump Subjects
Link to the Mc Nally home page