Inoperative diaphragm pump questions

[Corby Dawson]

Hi,

I'm playing with a Danielson 280250 dual diaphragm pump. I think it was originally out of one of the Tribodyn systems.
The problem is that it will not run!
I can turn it by hand and feel the pumping when holding a finger over the port.
When I plug it it it just hums, sometimes it tries to run but then halts. (Never moves more than one turn)
If I try and turn it by hand when plugged in it resists turning in either direction and if I spin it in the correct direction it still does not run.
I do not leave it plugged in over 5 seconds.
The run capacitor measures around 7uf but has no marking on it.
The run winding measures 6.5 Ohm and the start winding measures 42 Ohms. (Seems a bit high???)
Anyone have any suggestions or maybe a working pump that could be measured for the resistance of the two windings? Also the value of the capacitor if it's marked.
Any help would be great!

Cheers,

Corby

[Jerry Biehler]

A capacitor may test fine on a handheld meter but be bad at operating voltage. I would just replace it and see what happens. The value is not overly critical but around 7uf sounds about right for a pump about that size.

[Richard Hull]

Start windings are always higher in resistance. Smaller wire for more turns. As the start winding is only engaged for a few moments and they want a ton of torque, they go for amp-turns in the start winding and pray the cap and cutout are good. This is why 98% of the motor burnups are the start winding. Centrifugal switch or capacitor issues cook the winding quickly..

Richard Hull

[Corby Dawson]

This pump does not have a Centrifugal switch. The run capacitor is connected all the time.
I tore the pump down and found the clearance on one side was off causing a mechanical binding when the motor was energized.
After fixing that the pump starts now, but once it is loaded down it halts!
I'm going to try another run capacitor and see if that helps.

Cheers,

Corby

[Jerry Biehler]

This pump does not have a Centrifugal switch. The run capacitor is connected all the time.
I tore the pump down and found the clearance on one side was off causing a mechanical binding when the motor was energized.
After fixing that the pump starts now, but once it is loaded down it halts!
I'm going to try another run capacitor and see if that helps.

Cheers,

Corby

Yep, those small motors are capacitor run, they use a capacitor to create a phase shift between the windings to make them run. I have a Jun-air compressor that has a very hard time starting under a load, I had to install a timer based air bleed to let it get running before it starts running.

Its possible that the motor may have been cooked from being in a stall state too long before you got it? Did you get it off ebay? If it was sold as used and not as "for parts" it must work.

-Jerry

[Sihao Huang]

I've had this happen to me before, and even though I do not guarantee this is the problem, it sounds suspiciously like it.
It might be the case that the bearings are not in good condition, or were somehow broken/stuck, thus preventing the motor from starting up due to the added resistance to its rotation. I'd take apart the motor and locate the two bearings, one at the back and one at the front, and check if they spin well. If not, order the replacement bearings. In my case it was indeed a faulting bearing and I removed it with a gear puller; replacing it with a new one. The pump worked perfectly afterwards.