Compressor Pressure Switch Adjustment

  1. PyroDan

    PyroDan Member

    Hello, been away from the forums for a while and just starting to get back into things.

    Last year I bought a Wolf Air 2HP 24L compressor from Screwfix. It's not that good but I did only pay £80 for it in an offer. Anyway I have a small problem with it. It's crap with a nailer, the cut in pressure is 4.5 bar and its cut out pressure is 8 bar. I'm finding that I need at least 6 bar with 40mm brads. So its ok to start, but the nailer stops sinking brads before the compressor kicks in.

    So today I finally got around to adjusting the pressure switch. Few pictures are in order...

    I tried adjusting the cut in pressure (down though, just in-case it was the cut out pressure) using the bolt on the top, turns out that it is the cut out pressure. however the cut in and out pressure seem to move together, so is this a fixed pressure switch? or am I missing another adjustment on it, I cant see one. I have set the compressor back to it's original factory settings for those concerned by the first picture :p

    Any help on this would be appreciated.
  2. rtbcomp

    rtbcomp Moderator Staff Member

    Sheffield UK
    The cut in and cut out pressure do follow one another, so when you adjust one you adjust the other. To increase the pressure turn the screw in the direction of the + arrow.

    The difference between the cut in and cut out is called the hysteresis.

    Some of the better pressure switches have an hysteresis adustment, this is usually marked with a triangle (delta) and +/- arrows.
  3. Robotstar5

    Robotstar5 Casanunda Staff Member

    I have a very similar compressor, first time I tried it the pressure kept going up until the safety valve blew!.
    Ignored warning about factory setting and reduced cut off pressure on switch so it shuts off before hitting the red zone on guage, worked OK after that.
  4. xpuser8334 New Member

    South Yorkshire
    Hi, - not meaning to hijack this post, but....
    can somebody help please?

    Putting this question in steps seems the easiest thing to do
    i have a CougarAir 25L 6.99cfm 1.5hp compressor with the same setup, but:-

    Step1 - when pressure is reached, the cut-off switch cuts out the motor (correctly) but blows air out of the switch itself - not the pressure release valve.

    Step2 - Once the pressure drops to the cut in pressure the motor starts again. until cut off pressure is reached.

    Step3 - The compressor goes back to step 1.

    As you can imagine this is annoying. so i bought a new 4 port pressure switch and fitted it, along with a new pressure release valve.


    interesting thing is.
    new switch block (with a twist switch instead of the pull button)
    new blow valve - the only things original are the Tank, Motor/Direct drive unit, cables and a tee peice which the compressor pump, tank and flexible pressure sensing hose is connected to.

    the same issue is happening.
    the max pressure of the compressor is 8 bar and the new switch will support upto 11 bar.
    the pressuse switch has been adjusted to cut out at just under 8 bar.

    the only exception to the rule is, with the twist switch in the OFF position the switch (not pressure release valve) blows off until empty!

    Am I going daft, or do i need to investigate the tee fitted to the tank and flexible pipe work?

    I can't find any other adjustment screws but the main one on top, but do i need to re-adjust this some how?

    Is the new switch i bought faulty too? (from machine mart local shop)

    Thanks for reading this long message, but it is starting to get on my nerves now!

    Last edited: Sep 14, 2008
  5. rtbcomp

    rtbcomp Moderator Staff Member

    Sheffield UK
    If I read your question properly, does the air keep coming out of the switch until the motor starts again, even though you're not using any air?

    If so that is a faulty non-return valve fitted in the tank where the pipe from the pump fits.

    It will happen with the manual switch because the knob operates the seame mechanism as the pressure switch.

    The air comes out of the switvh cover because the dump valve is inside there. The external release valve is only there to release excess pressure should the motor fail to stop.

    Look here
  6. xpuser8334 New Member

    South Yorkshire
    Hi, the pressure builds up (not blowing out of the switch) and then the switch cuts out correctly.

    The switch then immediately after cut-off, starts to blow out air - not through the blow off valve though.
    once the pressure has dropped to the Cut-in pressure, the motor starts - the air stops blowing out, and the pressure builds up again.
    then the cut-off kicks in, and we lose air again through the switch.

    Ever decreasing circles so to speak.

    this is without any airlines, attachments etc. plugged in.
    Only the compressor - mains power, and the switch are used.
    Do i need to inspect / clean the chromed "TEE" piece on the tank, which connects the pump, tank and flexi pipe to the switch.


  7. rtbcomp

    rtbcomp Moderator Staff Member

    Sheffield UK
    The dump valve in the switch is working correctly. I don't know what you mean by the blow-off valve, if you mean the brass thing screwed into one of the ports on the switch that is a safety valve as I explained above.

    As explained in the link above, you should be looking at the non-return valve on the tank, ie the thing you refer to as the T-piece.
  8. xpuser8334 New Member

    South Yorkshire
    i will give it a go!

    Yes the Blow-of valve is the safety valve - I must stop using OLD style lingo!
    Thanks Again!