Troubleshooting a Faulty Fuel Pump: How Does It Work?

[Axefly]

Good Morning

Please can anyone help, i would like to know if an engineer can tell me how this fuel pump works, I'm trying to establish if it is faulty or not, my actual fuel pump is shown in the pictures below, when i try to suck on the outlet or blow into it, i cannot get air through it either by suction or by blowing through it, Should it be like that ? or should i at least be able to get some air through it both ways ?

 

[Axefly]

Would anyone perhaps know ?

 

[Travis_King]

Well you certainly wouldn't be able to get air through from the discharge side. There's a check valve on the discharge which maintains pressure in the downstream fuel lines by not allowing anything to flow back through the pump. As for blowing through the thing, I'm not sure. Tolerances are typically pretty tight, especially for turbine/impeller-based pump. They are typically flow-through devices, meaning the oil flows through the whole thing, but I can't tell you what the spring constant is of the spring that holds the check ball in it's seat. These things develop pretty good pressure, a lot more than you can produce with your lungs.

Though, tight tolerance / high rpm impeller based pumps are more prone to contamination issues and clogging than other types of fuel pumps.

 

[Axefly]

Thanks Travis, is it possible that it could have a solenoid actuated valve that only allows for flow when the pump is inside the petrol tank ? (coming to think of it, i get the feeling that is actually what you jusr said by referring to a "check" valve. Is it electrically activated/controlled, would i be able to fool it, See what I'm trying to do is simply put the in tank petrol pump into an external container with fuel and adding current through it to see if it works, However what i did so far is directly adding 12 volts to the motor itself, i did not apply 12 volts on the the actual pump connector, could it be that it activates the valve should i apply current on the pump connector itself, (solenoid perhaps connected to the physical pump connector ?)

 

[Travis_King]

I would be surprised if the check valve was controlled by a solenoid, as they are typically found as seen in your drawing. Though admittedly I do not know an extensive amount about electric fuel pumps. In general, check valves are manual (just one less thing to go wrong, and you don't really need control on it, it's a simple operation: let stuff go one way, don't let stuff go the other way).

What do you mean you applied 12 V to the motor itself, and not the pump connector? Pumps are mechanical, motors are electric. This pump operates because the induced magnetic field spins the armature when current is applied to the solenoid. If you aren't applying the power correctly to the motor, that's why it's not working...

 

[Axefly]

Attached below is 2 pictures, encircled in yellow is where iAttached below is 2 pictures, encircled in yellow is where i connected the 12 volts (i removed the wires first) then connected it to the wires of the motor.

when i ran the motor and try to blow or suck, at the external pump outlet i could still not get any air through either way, could it perhaps have something to do with the connector at the bottom of the motor as seen in picture, Or could the impeller be broken ? The filter was crystal clean when i removed the pump, so i cannot see that it is at all filled with debris.

 

[fleebell]

That turbine disk pump isn't going to pump air (it's not designed for air) and you can't generate enough air pressure blowing into the inlet to open that outlet spring. You could probably use compressed air at the pump inlet to make it open and allow air to flow through it but that wouldn't serve much purpose other that showing whether the one way outlet valve works or not. From your statements above, it evidently does work.

If your applying dc directly to the motor leads and it doesn't spin the odds are very high you have a bad motor. Somewhere in there a wire has come loose or maybe a bad brush connection.

If it does spin don't run it without being immersed in the operating liquid more than a few seconds though as it's designed to be cooled by the liquid and will probably overheat very quickly running it dry. That could also possibly damage any mechanical seals in if there are any.

If it does spin but doesn't pump when the inlet is submerged in the operating fluid the the odds are the turbine wheel hub has broken loose from the motor axle or the outlet valve is stuck. If you can get compressed air through it by blowing into the pump inlet the the turbine wheel is probably broke and it's not a stuck valve.

Also I know it sounds silly to state the obvious but make sure the polarity of the electricity supplied is wired correctly. While that motor might may backwards, it will not pump when doing so and will quickly overheat.

 

[Axefly]

Thanks so much Fleebell for that brilliant explanation, i have put the pump in a bucket with petrol and good news it's working :) I now am ruling out pump failure, and hopefully just an electronic problem like a relay in my car, or a blocked pipe,
(hope the pump is still pumping sufficient pressure, i don't have a meter to test that, however pinching the fuel line has hard as i can still petrol flows through the line, my initial thoughts are that it's good enough and the engine should be able to get fuel from the pump.

I knew i had place my question at the right place :D !

Again thanks :D ! !