8 pumps for food use or potable water, 6 maintenance, 1 general – Flowserve NMD User Manual

Page 22

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Page 22 of 40

5.7.3 Pump speed
Changing pump speed effects flow, total head,
power absorbed, NPSH


, noise and vibration. Flow

varies in direct proportion to pump speed, head
varies as speed ratio squared and power varies as
speed ratio cubed. The new duty, however, will also
be dependent on the system curve. If increasing the
speed, it is important therefore to ensure the
maximum pump working pressure is not exceeded,
the driver is not overloaded, NPSH




, and

that noise and vibration are within local requirements
and regulations.

5.7.4 Net positive suction head (NPSH



NPSH available (NPSH


) is the head available at the

impeller inlet, above the vapour pressure of the
pumped liquid.

NPSH required (NPSH


) is the minimum head required

at the impeller inlet, above the vapour pressure of the
pumped liquid, to avoid excessive cavitation and
extreme performance degradation.

It is important that NPSH




. The margin

between NPSH




should be as large as


If any change in NPSH


is proposed, ensure these

margins are not significantly eroded. Refer to the
pump performance curve to determine exact
requirements particularly if flow has changed. If in
doubt please consult your nearest Flowserve office
for advice and details of the minimum allowable
margin for your application.

5.7.5 Pumped flow
Flow must not fall outside the minimum and
maximum continuous safe flow shown on the pump
performance curve and or data sheet


5.8 Pumps for Food Use or Potable

If the pump has not been specifically ordered for a
food or drinking water application it must not be
used for these types of applications. If it has been
ordered for this type of application the following
recommendations are to be followed.

5.8.1 Cleaning prior to operation
Pumps that are to be used for a food or drinking
water application should be cleaned before being
put into initial operation and after the installation of
spare parts that are in contact with the liquid.

Cleaning once the pump has been commissioned
will depend on the application and operating
conditions. The user must ensure that the cleaning
procedures are suitable for the application and
operating conditions, and local regulations.


6.1 General

If a belt drive is used, the assembly and

tension of the belts must be verified during regular
maintenance procedure.

In dirty or dusty environments, regular checks

must be made and dirt removed from areas around
close clearances, bearing housings and motors.

It is the plant operator's responsibility to

ensure that all maintenance, inspection and
assembly work is carried out by authorized and
qualified personnel who have adequately
familiarized themselves with the subject matter by
studying this manual in detail (see also section

Any work on the machine must be performed when it
is at a standstill. It is imperative that the procedure
for shutting down the machine is followed, as
described in section 5.6.

On completion of work all guards and safety devices
must be re-installed and made operative again.
Before restarting the machine, the relevant
instructions listed in section 5, Commissioning, start
up, operation and shut down
must be observed.

Oil and grease leaks may make the ground
slippery. Machine maintenance must always
begin and finish by cleaning the ground and the
exterior of the machine.

If platforms, stairs and guardrails are required for
maintenance, they must be placed for easy access
to areas where maintenance and inspection are to
be carried out. The positioning of these accessories
must not limit access or hinder the lifting of the part
to be serviced.

When air or compressed inert gas is used in the
maintenance process, the operator and anyone in
the vicinity must be careful and have the appropriate
protection. DO NOT SPRAY air or compressed inert
gas on skin. DO NOT DIRECT an air or gas jet
towards other people. Never use air or compressed
inert gas to clean clothes.

Before working on the pump, take measures to
prevent an uncontrolled start. Put a warning board
on the starting device with the words:
"Machine under repair: do not start".
With electric drive equipment, lock the main switch
open and withdraw any fuses. Put a warning board
on the fuse box or main switch with the words:
"Machine under repair: do not connect".

Never clean equipment with inflammable solvents or
carbon tetrachloride. Protect yourself against toxic
fumes when using cleaning agents.

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