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evaluation to the factors that will encourage or even ensure increased
reliability of the pump.
The most straightforward method is to assess a penalty to any factors in
the evaluation which can be considered less than ideal. The penalty can
take a variety of forms and may often be fairly subjective. However, the
more objective the assessment, the more reliable the evaluation will be.

5.3.3 Factors involved in mechanical suitability

5.3.3.1 Mechanical seals
The most obvious example is the mechanical seal as it is that part of a
pump that most frequently fails. Consequently it is highly
recommended that a decision on which seal supplier, model and
materials is needed should be finalized up front and included in the
pump specification. This helps all pump vendors and ensures you get
what you really need, rather than the cheapest available on the market.
However, if a variety of seals have been offered in the various bids
received, there are a number of design features which can be clearly
identified and evaluated.
(a) For example, the cartridge design is simpler and safer to use than
the component seal. It protects the seal faces against damage and
reduces the time and skill level required for installation. It can be
argued that a sound evaluation assessment for not providing a
cartridge seal may be the addition of the cost of an additional
spare seal of the type originally quoted.
(b) Any seal which has a dynamic secondary seal will inevitably cause
fretting corrosion which leaves a damaged shaft. With this type of
a seal, the shaft must be protected by a sleeve which will require
frequent replacement. A non-fretting design will not need a shaft
sleeve, thus eliminating one spare part. It also allows a larger
diameter (and thus a stronger) shaft.
One suggestion would be that, when a fretting seal design is offered,
the bidders could be assessed an amount equal to the value of one
sleeve every two years. A similar kind of assessment can be conducted
for the various types of springs or bellows used as some are more
suitable than others for different services.

5.3.3.2 Seal environment
A large bore seal chamber will permit any mechanical seal to last longer.
If any bidders do not offer this, they could be assessed the price of an
additional spare seal of the type originally quoted.

-- j