Well the AMETEK blowers arrived. Large motor with a relatively compact blower unit. These little units spin at up to 22000 RPM ! I tested the units and they work from 4V to 12V with 4V providing a nice gentle flow of air and 12V creates a screaming banshee of a blower more suited to leaf blower applications
The open port of the blower is already too powerful an air flow for SMT work at 6V operation but I thought I would do some really crude tests on this powerful little unit with regard to creating back pressure at the output port by partially covering it with my finger. The results were interesting and tally with what we have previously discussed in this thread. Bear in mind that the AMETEK blower is rated to produce over 700l/m at 10V with a 2.5A draw.
I powered the blower with 10V and she spun up to ~18000 RPM and a powerful jet of air was produced at the output port. Trying to reduce the output port diameter with a finger met with decent resistance from the air flow. It also created a powerful smaller jet of air. Starting from ‘off’ with my finger partially covering the output port resulted in very little pressure against my finger and a far reduced jet of air coming out of the smaller port. The blower did not ‘like’ the back pressure at all. I reduced the voltage on the fan to see how it behaved and proved that when running ‘open port’ of around 15mm diameter, it spun up well and created decent pressure. Partial obstruction of the output port progressively reduced the blowers performance from ‘cold start’ and virtually destroyed its ability to create decent pressure.
To me this tallies with not only the AMETEK data sheet but also the behaviour of the hot air stations that use such centrifugal blower designs. The blowers in those hot air stations are large and powerful yet produce only 120l/m air flow when running at high RPM. It would appear that the blowers are ‘suffering’ from ‘inadequate’ output port diameter influences on their ability to create pressure and flow. Now before readers think this is a criticism, it is not. It would appear that the manufacturers of the hot air stations realise how the centrifugal blower will respond to reduction of the output port diameter when SMT rework nozzles are fitted and proportioned the blowers size and performance to compensate. As a result, the powerful blower does not produce its ‘normal’ ~800 to 1200 l/m but a more appropriate ~120l/m maximum due to back pressure effects on the centrifugal blower operation. It does produce the required air movement and pressure for the hot air workstation but the pressure and flow is influenced by the output nozzle size. The smallest nozzle sizes will likely create an ‘interesting’ air flow within the blower that almost destroys its ability to create much pressure at the output port but the size and power of the blower still creates enough for the task at hand. I found it interesting to see that if the AMETEK blower was allowed to ‘spin up’ to a decent speed and then had its output port partially obscured, it provided more pressure than if it was started with the output port already obstructed. I presume this has something to do with the effects of back pressure on the impellers ability to create the best air movement within the blower housing.
This has been a very interesting little experiment and it was nice to see the centrifugal fans response to output port size and back pressure that tallied with technical papers that I have read on the topic. Basically, centrifugal blowers are great at shifting large volumes of air and can create pressure provided the output port flow is unobstructed. Such blowers can be ‘abused’ by obstructing the output port provided the effects are understood and managed
Fraser
Home
Help
Search
Login
Register
