The description of the part states that: “The direction of the airflow can be changed by reversing the polarity of the motor.”
However, when reversing the polarity the pump I have only “sucks”. That is, the air is blowing out of the central port and sucking in the side port.
When I say reversing the polarity of the pump, I am literally switching the positive and negative terminals from the power supply, going from a positive voltage (+4.8V) to a negative one (-4.8V).
Interesting. I wonder what sort of air pump that is. I strongly suspect it could be a “squirrel cage” type. If so the blow and suck will not reverse and the volume of air will only decrease. I wonder if anyone has actually tried this or is it only a reprint of the blurb provided by the supplier.
I have had some experience with this sort of thing in high power transmitters where this type of blower is used for cooling. Sometimes a transmitter would not come on and the first check was blower rotation. While the unit still supplied some air it would not be enough to operate the air supply interlocks. These were usually 3 phase motors and sometimes a phase got accidentally reversed somewhere. The only thing this usually affected was rotating motors.
I have seen one reference that it might be a diaphragm pump, but I can’t confirm that. It would be unusual for an air pump to use a diaphragm, but possible. If so then the direction of flow is controlled by valves in the pump chamber, and is the same for either direction of rotation of the motor.
Another case of pertinent information not being available. The Core blurb is a direct copy of the DfRobot page which does not seem to have any more info.
Jeff. You could well be right. The pics show a dark gasket looking thing as part of the pump assembly which could be a diaphragm. If it is you a quite correct in saying the motor direction will have no control over air flow.
Maybe Core could investigate and apply any corrections to the description. I realise it would be a monumental and not viable task to closely check the description of every sourced item but if spot checks could be done when time permits it might weed out those suppliers who have suspect descriptions or claims. Or, when this sort of thing is spotted at least check that product and investigate if errors are evident.
When reading through some of the posts I personally tend to regard ALL descriptions and claims as suspect until proven otherwise. Sad situation but in the present climate one I feel safest.
I can see logically how reversing the polarity of a brushed DC motor would make the motor component reverse direction but as @Robert93820 and @Jeff105671 have hit upon it depends on the construction of the pump mechanism as to whether this will reverse the flow of air through it.
Regretfully we don’t have any stock on hand that I can test to see if it behaves the same as your unit, but we do have a shipment due to arrive on Monday. I’ve made a note to test the stock as it arrives and if we aren’t able to reverse the flow as we’ve been advised we’ll contact the manufacturer and follow up with them.
I’ll report back here once we’ve got some stock we can experiment with and get to the bottom of this.
Hi Bob and @Jeff105671,
Just following up with an update. We’ve tested the latest batch of pumps we received and have confirmed the flow direction is not reversible as you both suspected. After confirming with the manufacturer this was an error in the specifications we have updated our product page to remove the incorrect claim.
We’ll make sure that anybody caught out by that incorrect specification has what they need to get their projects back on track.
Thanks for your help in diagnosing this issue.
Thanks for that