Flowserve MP1 Sier-Bath - Manual (Page 26)

MP1 USER INSTRUCTIONS ENGLISH 26999958 – 10-12
Page 26 of 48 flowserve.com
pressure. The amount the slip increases is a function
of the viscosity of the liquid and the higher the
viscosity of the liquid, the lower the slip. The
displacement minus the slip is the capacity the pump
will produce.
Normal operation of the pump will eventually produce
wear on internal components resulting in increased
internal clearances. This will increase the slip and
reduced performance may be experienced. At this
point, rotating components may have to be refurbished
or replaced to maintain original performance.
Never operate a positive displacement pump to any
pressure in excess of the maximum pressure indicated
on the nameplate. If the original conditions must be
changed for any reason, consult Flowserve.
A multiphase pump is designed to handle two phases,
one a liquid, the other a gas. At high Gas Void
Fractions (GVF) sufficient liquid must be available for
recirculation through the pump. The fluid is being
recirculated so that it may form a seal between the
pump’s bores and the screw’s outer diameter. Fluid is
retained by the pump in the volume between the Inner
Casing and Outer Casing. It enters the suction
chamber by means of four orifice plugs in the Inner
Casing.
At high gas void fractions like values of 100%, there
will be a limited time that the pump can operate without
overheating. If the pump is to be operated at very high
Gas Void Fractions for extended periods, water must
be injected into the suction line to limit the
operating
temperature of the pump. As a rough guide the amount
of water to be injected will be approximately 4% of the
pump’s capacity.
5.11.2 Specific gravity (SG)
Pump capacity and total head in metres (feet) do not
change with SG; however pressure displayed on a
pressure gauge is directly proportional to SG. Power
absorbed is also directly proportional to SG. It is
therefore important to check that any change in SG will
not overload the pump driver or over-pressurize the
pump.
5.11.3 Pump speed
Changing pump speed effects flow, power absorbed,
NPSH
R
, noise and vibration. Pump displacement
varies in direct proportion to pump speed. However,
the new duty 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
A
>
NPSH
R
, and that noise and vibration are within local
requirements and regulations.
5.11.4 Net positive suction head (NPSH
A
)
NPSH available (NPSH
A
) is a measure of the head or
energy available in the pumped liquid, above its
vapour pressure, at the pump suction branch.
NPSH required (NPSH
R
) is a measure of the head
required in the pumped liquid, above its vapour
pressure, to prevent vaporization of the liquid. This
phenomenon, called cavitation, can cause serious
damage
to the pump and adversely affect
performance. It is important that NPSH
A
> NPSH
R
to
avoid vaporization of the liquid. The margin between
NPSH
A
> NPSH
R
should be as large as possible.
NPSH
A
is affected by changes in the liquid
temperature and vapour pressure, the altitude of the
installation, entrained gasses in the liquid, and the
viscosity of the liquid.
If any change in NPSH
A
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.
5.11.5 Pumped flow
Pump displacement varies directly with speed. The slip
or leakage from discharge to suction through the
internal clearances varies with differential pressure
and viscosity. The pumped flow is the displacement
less the slip.
5.11.6 Pressure surges
The pump must not be subjected to pressure surges
such as may be caused by water hammer or sudden
check valve closure.