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Wood Pellet Stove Vacuum Switch?

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by Don2222, Jan 15, 2012.

  1. Don2222

    Don2222 Minister of Fire

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    Hello

    The Pelpro has a 2 port switch but it uses the negative pressure port.

    Does anyone know the typical spec for Water Lift on the input?
    Here is a nice METAL adjustable one from grainger. It is adjustable from 0.12 - 5.0 inches of water
    http://www.grainger.com/Grainger/CLEVELAND-CONTROLS-Air-Sensing-Switch-4XB70?Pid=search


    Good description here with a Whitfield Vacuum Switch
    http://www.thepelletstovecorner.com/tips-ideas/the-vacuum-pressure-switch/

    The switch is easily identified because it is connected to hose or tube of about 1/4″ diameter that runs to the exhaust fan housing or somewhere on the stove body that communicates to typically a negative pressure environment created by the exhaust fan. The idea here is that the exhaust fan, downstream of the burnpot, is “sucking†the smoke, heat, and particulate created by the burning pellets, in turn, fresh air is drawn through the holes in the burnpot providing the oxygen and turbulence required for a continued efficient fire. There is a diaphragm located within the vacuum pressure switch, as long as the exhaust fan is doing its thing and the required minimum negative pressure is maintained, the diaphragm is pulled closing the switch allowing electricity will travel across it. The switch is hooked up to the auger motor. So, if the exhaust fan fails or the stove door is left open the auger motor should stop feeding pellets to the fire. Or, if your stove or flue is clogged up the auger motor should stop feeding.

    To review, the vacuum pressure switch allows the auger to run as long as there is sufficient negative pressure.

    If you are sure the exhaust fan is running properly and the stove and flue are clean, and the auger appears not to be jammed and you are positive that all doors are sealed, (check the ash drawer door), and the auger motor fails to turn, you very well may have a problem with the vacuum pressure switch.

    The first thing you want to do after you unplug the stove is examine the hose looking for a break, if its broken the break will most likely be where the hose connects to the stove as that is where the hose is exposed to the most heat. Next, disconnect the hose from the switch and see if you can blow air through it. If you can’t you will want to ream out the metal tube that the hose connects to with a stiff wire.

    If none of the above corrects the problem you will want to bypass the switch temporarily to see if it needs replacing. The switch will have two wires connected to it, but some switches will have three places to connect to so take a good look before you disconnect the wires from the switch. A simple trick to bypass the switch is to use a flat type automotive fuse and connect the wires from the switch (they have female spade type connections) to their male counterparts on the fuse. Check it out, does the auger work with the vacuum pressure switch bypassed? If it does and the fire burns bright and clean with no sooting of the glass then you will need to replace the switch. I do not recommend leaving the switch bypassed! It is a safety feature designed to shut off the auger in the event of a exhaust fan failure or a flue blockage.

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  2. jtakeman

    jtakeman Minister of Fire

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    Careful don, On low my Omega is right about 0.08, If you miss the low nuber you could get issues. If I slide my damper in I can go as low as 0.05 before I hear the switch cut out. FYI
  3. Don2222

    Don2222 Minister of Fire

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    Hi Jay

    Thanks, so the switch should be set to 0.5 Inches of Water Lift and the non adjustable ones are set to 0.5 right?

    I think the Pelpro vacuum switch is not working low enough to always come on?
  4. jtakeman

    jtakeman Minister of Fire

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    IS the pelpro a damper stove? The more you open the dampr the more draft you get.

    I'm not sure I'd guess at what switch it needs. To high and it won't run. To low and it could run with a plugged vent. If you have a mag you can check and see where it cuts out. If you think its too high? Id get teh adjustable and tweak it in. Or just get the OEM switch for it and be sure its right.

    keep us posted
  5. Don2222

    Don2222 Minister of Fire

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    Yes, it is the Pelpro but OEM switches are always alot more expensive and in this case all plastic!


    OEM part $39.00
    http://www.sunburst-sales.com/PHPpa...hp?pageNum_rsDansons=1&totalRows_rsDansons=51

    For $27.00 the adjustable should work.

    Where do you put the mag for the measurement?

    Also thanks for mentioning the damper, I will try it wide open just to see if it starts!!
  6. jtakeman

    jtakeman Minister of Fire

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    If the stove doesn't have a port? Use a tee and go right into the vacuum hose. I'd buy the mag first. Could be you have the draft set to low. Pull the damper out and see?
  7. Don2222

    Don2222 Minister of Fire

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    I just tried it with the damper almost closed and wide open. Did not make a difference so looks like the switch is not working very well at 23 degrees in the shed. I wonder if the switch can be cleaned??
    I can try again tomorrow at about 50 degrees if I buy more kerosene!
  8. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    Don does the combustion blower fire up to speed or does it complain?
  9. Don2222

    Don2222 Minister of Fire

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    Hi Smokey

    The combustion blower fires up with no complaints but it does not seem to be running very fast. Is that because the stove is cold?

    Also I am not sure about something else. when I plug the stove in, the convection and combustion blowers come on immediately without pressing the start button. When I press the start button the red heat setting light comes on and that is when the auger should turn but does not.

    L120 - $18.00
    http://www.sunburst-sales.com/PHPpa...hp?pageNum_rsDansons=1&totalRows_rsDansons=51
    L120 - $19.95 - This is better
    http://spaplaceinc.com/products.php?cat=18&pg=4
    Here is the Low Limit Switch description in the Pelpro manual. Unlike other stoves it looks like it Opens above 120 degrees and should be closed at the lower temp. I tested mine and it is Open with the stove off!
    So that would mean the switch is bad??

    L120 LOW LIMIT SWITCH
    This limit switch is mounted on the exhaust blower housing and has 2 main functions:
    Should the fire happen to go out, for any reason, this limit switch will shut the stove off when the exhaust
    temperature drops below 120° F.
    Upon starting the appliance, the AcuTron control board has a 15 minute “Lighting Modeâ€, if the stove
    exhaust does not reach 120° F in that 15 minutes the stove will shut off. As soon as the stove
    exhaust does reach 120° F, the limit switch opens and the AcuTron enters a 5 minute “Safety Delay†mode
  10. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    If the combustion fan doesn't get up to proper speed it won't cause the vacuum switch to close. Anything that affects metal can have an impact on a combustion blower cold causes metal to contract and lubricant to thicken. Both can put drag on the blower.

    ETA: Some stove controllers power up the blowers as part of set up to ensure the electronics has a valid value in the control registers.
  11. jtakeman

    jtakeman Minister of Fire

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    I'm with bear, Keep starting it and let the blower warm up. She'll go sooner or later!

    Last resort, Bypass the switch and fire it up for a while. The shut it down and reconnect the switch. If it fires right up its the cold slowing the blower do too much.
  12. Don2222

    Don2222 Minister of Fire

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    Yes, I agree with both of you. I am going to bring the shed to 55 deg and use that as a baseline.

    There is one other item. The Low Limit switch is different than most stoves, from the description in the manual I just posted in my prior post, it looks like it is open on rise and should now be closed. That may mess up alot of things like the fans not shutting down when the stove is off. also it could prevent the combustion blower to run at a higher speed in the start-up cycle. So looks like I should fix that first? I can also by pass it wit a jumper to see what happens!

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