Installation notes for vee belt drives

1. Pulleys should always be fitted so that the effective centre Of the belt or rope is as near as possible to the motor or fan bearing.

2. The load must not in any case be applied beyond the end of the fan or motor shaft extension.

Correct installation both shafts and pulleys are parallel and aligned

Shafts are not oorrectly aligned although they appear parallel when seen from above

The dotted lines indicate the faults and show the correct position Figure 11.12 Frequent installation faults for vee rope drives

3. To avoid the danger of imposing excessive stresses, it is advisable to consult the fan and motor manufacturers for all drives on shafts above 48mm diameter.

4. It is recommended that only direct coupled drives be used for motors in sizes D160M and above at 2-pole speeds.

Clean all oil and grease from pulley grooves and bores.

Remove any burrs or rust.

Reduce the centre distance until belts can be placed in the pulley grooves without forcing.

Align the pulleys correctly using a straight edge to ensure that the pulleys are in line and the shafts parallel, (see Fig­ure 11.12)

Tension the drive using the motor slide rail bolts.

10. Check that the vee belts are correctly tensioned (see Fig­ure 11.13):

A) Measure the span.

B) Apply a force at right angles to the belt at the centre of the span.

C) This force should deflect one belt 0.016 mm for ev­ery millimetre of span length.

Deflection 16 mm

D) The average value of the force in each belt should be compared with Table 11.5 and should initially be tightened to the higher values. If the measured force falls within the values given in Table 11.5 the drive tension should be satisfactory. A force below the lower value indicates under-tensioning. When starting up, a new drive should be tensioned to the higher value to allow for stretch during the running in period. After the drive has been running a few hours the tension should be re-adjusted to the higher value. The drive should be re-tensioned at regular maintenance intervals. Make adequate provision for tensioning the belts during their life.

Belt section	Small pulley pcd (mm)	Belt speed
		0 to 10 m/s	10 to 20 m/s	20 to 30 m/s
SPZ	95	12 to 18	10 to 16	8 to 14
	95	18 to 26	16 to 24	14 to 22
SPA	140	22 to 32	18 to 26	15 to 22
	140	32 to 48	26 to 40	22 to 34
SPB	250	38 to 56	32 to 50	28 to 42
	250	56 to 72	50 to 64	42 to 58
SPC	355	72 to 102	60 to 90	50 to 80
	355	102 to 132	90 to 120	80 to 110
Z	50		4 to 6
A	75		10 to 15
B	125		20 to 30
C	200		40 to 60
D	355		70 to 105

Table 11.5 Correct vee belt tensions: required force N at centre of span for belt speed

To obtain kgf divide N by 10 to give the approximate value.

Note: These figures are reasonable for most applications but should be

Checked with the manufacturer for specific installations.

Posted in Fans Ventilation A Practical Guide