General Guidance for
Polyfan Fan and Component Selection
For basic configuration of Polyfans units
all parties concerned with the selection process need to consider
suitability and compatibility of components that combine to provide the finished product. It is assumed that before
embarking on this product design selection process the client or their appointed
representative has satisfied
themselves that a direct driven polypropylene centrifugal fan from the
Polyfan range is suitable for the intended application.
In the example that follows an assumption is made that electrical motors will be used to drive the
Polyfan unit, and where the purchaser obtains components only for self assembly
that they have sufficient knowledge and skill to assemble the
All information given should be cross-referenced with the 'Polyfan
1 - POLYFAN SIZE AND DUTY
STAGE 2 - MOTOR SELECTION
STAGE 3 - POLYFAN
1 POLYFAN SIZE AND DUTY.
Using the fan curves provided in the 'Polyfan catalogue' select
a fan that can provide the performance required. The Polyfan performance
curves provide information on
It is preferable to select a fan that operates within its most efficient
zone on the fan curves. For this exercise we have assumed that the
requirement is for a direct driven fan to provide 400 m3/h against a total
pressure of HT10mm (98 Pa) with an outlet velocity below 7m/s when
operating at a 6 pole speed (less than 1000 RPM) with an absorbed power in
the region of 0.15HP (0.11 kW) using a 240 volt single phase supply.
- Volume flow Q (in m3/h)
- Pressure HT (in mm)
note: Pa =HT x 9.80665
- Fan outlet velocity in Vu (in m/sec)
- Fan outlet velocity pressure Hd (in mmH20)
note: Pa = mmH20 x 9.80665
- Absorbed Power HP
note: kW = HP x 0.746
- Rotational speed N (in revs per min)
- Efficiency shown as %
By reference to the Polyfan fan curves firstly consider the volume flow
of 400 m3/h against a pressure of HT 10. There are several fans
capable of providing this duty but as a direct driven machine the VSB 20
operating at 950 RPM (6 pole) is the one selected. See 'Polyfan Calculation
Sheet VSB 20'
Follow the horizontal line for pressure HT10 (98 Pa) across to the right until it dissects the vertical line from
400 m3/h. You will note at this position the two lines dissect
between the 54% and 56% efficiency line and are below the dark arced line denoting the rotational
speed of 950 rpm (6 pole).
Reference to the broken chain dotted arc line will confirm that the
absorbed power is below the 0.15 HP (0.11 kW) specified. Projecting
vertically down from the 400 m3/h point the outlet velocity is
confirmed at 5.3 m/sec and extending this line indicates the outlet
pressure as 1.8 mmH20 (18 Pa).
From the information obtained above, it is confirmed the VSB20 driven by a
6 pole motor should provide the performance required. The next stage will
consider implications of the direct driven motor selection for the VSB20
in this example. Selection should consider that motor manufacturers
quote motor speeds as 2, 4, 6 & 8 pole. Dependant on supplier and type
with a 230/240 volt 50 Hz 6 pole motor speeds can be in a band of 840 to
920 RPM + or - 10%.
STAGE 2 MOTOR
The Polyfan range can be connected to most electric motors subject to
the frame size of the motor being suitable to accept the impeller,
impeller fixing screw, back plate closing flange, sealing gland and
mounting stool. In the design of the Polyfan range consideration was given
to European metric framed motors and standard frame sizes available.
response to request for standardisation of motor sizes within the range it
was decided that 0.18kw would be the lowest power of motor used and kw
powers below 0.18kw illustrated for the VSB14, VSB20, and VSA 20 have been
uprated to 0.18kw. A Polyfan VSB 20 operating at 1450
RPM (4 pole) would be fitted with a 0.18kw 4 pole motor in a 63 frame and
11 mm dia shaft. For this example the 240 volt single phase Polyfan VSB 20 operating at 950 RPM
(6 pole) will be fitted with a 0.18kw 6 pole motor in a 71 frame with a
14mm dia shaft.
All Polyfan units require the shaft to which the impeller is secured to
have a tapped thread in the shaft and a keyway.
The fundamental fixing arrangement relies upon the keyway providing
rotational stability whilst the threaded shaft accepts the specially
designed encapsulated fixing screw to secure the fan impeller onto the shaft. A further
requirement is for the shaft length to be sufficient to accept the impeller boss
and fixing screw.
The voltage at which the fan will operate will also effect the motor
fitted. It is often the case that the motor frames for an identical fan
case to provide identical duties will vary in the motor frame and impeller
bore as a consequence of one being 240 volt and the other being 38/440
For guidance we have prepared a schedule of the more commonly used
impeller, back plate and fixing screw arrangements ' Polyfan
impeller sizes/Rotations schedules'. It is important when
specifying motors for Polyfans to ensure consideration is given to the
- Motor power, voltage and pole speed.
- Motor frame has a female thread to suit the Polyfan fixing screw for
the fan size.
- Motor frame has a standard metric keyway.
- Motor full face flange is suitable for the Polyfan back plate closing
- 'Polyfan Impeller size and rotational schedule'.
For the VSB 20 shown in the example the motor selection is as follows
- Motor Power 0.18KW
Sufficient for the 0.05KW absorbed power.
- Motor Speed 6 pole (850 RPM)
Sufficient for RPM required.
- Motor Shaft 14mm dia tapped M5 x 25 deep with 5mm keyway and
Suitable for VSB/20 impeller see 'Polyfan impeller
- Motor voltage 230/240 volt single phase
Suitable for clients specified voltage.
- Motor mounting foot mounted B3 with B5 flange
Suitable for 71 Polyfan closing flange see 'Polyfan
impeller sizes/Rotations schedule'.
For guidance the 'Polyfan catalogue' has a small table showing
some typical performance duties with motor speed and power. In some
instances to facilitate motor frame compatibility it may necessary to
consider a motor with a kW capacity exceeding those shown. Selection
should consider that motor manufacturers quote motor speeds as 2, 4, 6
& 8 pole. Dependant on motor supplier and type with a 380/440 volt 50
Hz 6 pole motor speed can be in a band of 820 to 960 RPM + or - 10%.
3 POLYFAN COMPONENT SELECTION
The components that can be interchanged on a known Polyfan fan size
(to suit the specified fan frame) are the back plate, closing flange and
impeller. Reference must be made to the 'Polyfan
impeller size/rotations schedule' to ensure the size required is
For a known rotational handing, for example with a Polyfan VSB 20,
whilst the fan case, inlet, gasket and stool are a common components,
there is a selection of three closing flanges and three impeller bores.
When ordering components state clearly the requirement. Italics
All orders should confirm the numbers of each component
- Polyfan Type and size - VSB 20
- Handing of Casing - LGO
- Closing flange type - 71 x 14ø for 130mm PCD B5 standard
- Impeller Rotation - LG clockwise at inlet
- Impeller hub bore - 14 mm dia.
- Impeller fixing screw - M5 x 25mm