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Discuss danfoss BFP pump solenoid stem in the Oil and Solid Fuel Forum area at PlumbersForums.net

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problemsolving a electro sterling burner and have narrowed thing down to the stem in the pump that the solenoid should activate- it appears to be seized solid - a magnet can't move it - the solenoid can't- and neither can I physically move the plunger with a lot of force. Time to replace it - or us it possible to free it off? Never had one of these out before......TIA!
 
If you've got 230v to solenoid and its not drawing iron plug in when energised then replace the stem, they're cheap enough.
Have you covered all other possibilities for no ignition as well? Just in case
 
I do have ignition - electrodes fire ok. I Checked volts to the solenoid and it was 13v at the start of the sequence then jumped to 65v and energised the coil enough to grab a screwdriver. So coil doesn't see 230v at that point. Control box is a bentone tf832.
 
The lower voltage you're seeing during pre purge is down to the mutual inductance between the motor and solenoid, so my understanding is. It is common to see around 50v during this time so my mentors told me.
If the coil drew in a screwdriver than that says the coil is energising with a sufficient magnetic force.
If you don't hear the distinctive click of the solenoid/stem at the time its supposed to then yes it would suspect them stem has seized based on the above.
Stems are cheap enough, I would also have a spare coil at hand, from what you've said I dont suspect the coil is damaged but it can go in your van stock if nothing else.
If a stem is partly stuck or fully stuck and the coil is energised for too long the faulty stem can burn the coil out. Basically in a steady state and sound stem/coil the coil is able to dissipate the heat generated from the flow of current, if the stem is faulty this affects the amount of magnetic flux passing through the coil windings and in turn affects the back emf, meaning a dodgy stem allows more current to pass and ultimately burn the coil out. Again based on your words above I doubt the coil is damaged but a spare can go in as van stock, if you don't already have some.
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Sorry I just re read your last post. I though you said coil does see 230v. What voltage do you have when signal should be sent to coil?
 
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Thanks - good point about coil damage - hadn't thought of that. The start sequence then - fan runs and I see 13v at the coil connector (with the connector disconnected from the coil). Ignition then occurs and at that point I see 65v at the coil connector - and a few secs later I get lockout. The whole sequence takes around 10-12 secs before lockout. Because of that timing before lockout I checked photocell and resistances do vary between light and dark - and with the pc disconnected I just see lockout with no ignition so I can't think there's a problem there. But should I be seeing the 230v? Got a new stem for tomorrow - no local stock today - so will try that with a new coil as backup....
 
If you dont have 230v at coil lead at point of ignition then i would check cell and control box in that order. If the cell senses false light during pre purge, be it from parasitic light or a faulty cell then the box won't send 230v to coil for ignition and goes straight to lockout. If you've disconnected the cell and tried the cycle again, still with no success then I'd suspect the control box.
As I mentioned above the lower voltage you see during pre purge is down to the mutual inductance between the motor and cell and at this point is irrelevant. When everything is OK you should get 230v at coil leads at point of ignition.
 
I am getting 230v at coil now - but noticed that the photocell has v high resistances - e.g .031 on the 2M range in the light and 4.0 on the 20M range in the dark - does that sound right for mz770s?
 
I couldn't say for sure off the top of my head but those readings seem about right for the satronic, obviously as the light conditions change the readings will as well.
So you have 230v at coil lead after pre purge? And you say the coil generates sufficient magnetic force to pull in a screwdriver?
That tells me cell is not seeing parasitic light and the box sends voltage to coil for oil flow to nozzle.
Now you need to determine if the pump supplies flow to nozzle, you could still have a faulty stem yes, you could also have a blockage downstream of the solenoid in the HP line to nozzle and including the nozzle. If you have fuel out of nozzle then you could have an ignition problem.
Do you know how to check for atomization of fuel at the nozzle safely?
It could very well be a stem and a simple swap rectifies it, however its best to be prepared in case its not.
Because you're a still a new member it takes time for admin to approve your comments. I was aware of a response some time ago but have only now had access to it incase you're wondering.
 
.....and the answer was......
the photocell - the strange thing was that on retest the pc dark had a very high resistance - higher than when i had tested it before and higher than the 2M ohms range that I could see. So on replacement normal service was restored. The new cell varied from .011 to .014 on 2M range - which is quite a small range albeit quite a high one. Anyway thanks for your input on this - everyday we learn something....
 
Just remember boxes text for stray light during pre purge. As I said cell was the first thing to check đź‘Ť
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Disconnecting the photo cell and trying ignition sequence again should have shown this fault
 
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