Question about Craftsman Air Tools & Compressors

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I have a craftsman 33gal air compressor model # 152938. i have a constant hiss (leak) coming from upper tube immediately behind the electrical box. upon some disassembly i found it's coming from the little spring/needle valve(?) that connects to the end of the tube. when i lightly pull the needle out the leak stops. i see the needle pushes against a spring plate that connects to the off/auto lever. is this needle valve not seating properly? the leak drops my tank pressure quickly enough to engage the motor every 5 minutes or so.

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  • fndrbss Oct 07, 2010

    I WD-40'd the valve and it seems to free and functioning okay. What I've noticed is, when the compr motor is running the little spring plate(connected to the auto/off lever) is in the down position (away from the needle) and when the motor stops the plate springs up. This pushes against the needle thus causing air to escape. I lightly pushed the plate down with a screwdriver so it didn't make contact with the needle and the leak stopped. First of all, what's the purpose of that needle? Second, is the spring plate supposed to make contact with the needle? If I had a parts schematic I could at least give the correct names of these things but I think you know where I'm coming from. Help! I'll give you 4 thumbs and toes up if you can fix/explain this.

  • fndrbss Oct 08, 2010

    919.152930
    Dumb question...is the rubber seal inside the valve? Any info on getting a new one?

  • fndrbss Oct 08, 2010

    Finally found a blow up pic of parts. It's called a pressure switch (searspartsdirect.com says it's no longer available and no suitable sub). I think I'm screwed...may have to try some local sears repair shop to find one.

  • fndrbss Oct 08, 2010

    I tried WD (it's called a pressure switch by the way) and still no luck. Someone else suggested a bad rubber seal in the valve. Naturally the part is no longer available...I'm probably screwed }:-(

  • fndrbss Oct 08, 2010

    Found out the part in question is called an unloader valve. Located one at mastertoolrepair.com for $20! Hope it works. Thanx for the help.

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  • Master
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Actually this valves opens when the compressor shuts off.The pressure switch (which is activated by the larger air line attached to the tank)has a lever that opens this small valve to bleed the air from the compressor so that when it restarts it doesn't start against the tank pressure. The switch is probably working as intended, as it is venting as it should. Most likely the check valve at the tank is not sealing, allowing the air to escape from the tank through the valve attached to the pressure switch.

Posted on Oct 09, 2010

  • Tom W Oct 10, 2010

    Note in my previous answer, I told you it was the pressure switch. Most like it is not bad. It is supposed to let air bleed out until line is empty. If you did need a new one square d makes pressure switches that would work. You can get one at an electrical supply or Graingers. The check valve I was referring to should be mounted either right into the tank, or the fitting closest to the tank. This keeps the air from leaking out of the tank back to the compressor. The vent valve on the pressure switch opens the vent when the compressor turns off. If the check valve leaks, then it will allow air to continue to escape. Some are "pilot" operated some are not. A good cleaning of this might work, but some have rubber seats that get worn.

  • Tom W Oct 10, 2010

    OH, now that you sent your exact model number I see the pr oblem. This a smaller compressor that has a minifold assembly the incorporates the check valve into it. You might try taking it apart and cleaning it. If there are any rubber parts inspect carefully. I did notice that they say these parts are not available either. The item you need is the check valve or restrictor. Part number CAC-1391 Try cleaning it. You might try this web site too: http://www.mastertoolrepair.com/mobile/s...

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  • Craftsman Master
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Remove the small tube and clean both the ends and shoot some cleaner (WD-40 or similar) down the tube. Reassemble. Make sure it it tight but don't strip or break it. There is a special tubing wrench available to properly tighten these brass connections. If you are careful, you can get by without using that special wrench.

What is happening: This tube you are working with supplies real time pressure to the control switch. When the pressure is down, the spring relaxes and allows the contacts to close energizing the motor. When the pressure reaches a predetermined setting, the spring compresses and opens the contacts turning off the motor. Any leak in your system will of course allow the bleeding off of pressure and will thus turn on the motor.

I hope this helps you with your leak. Thanks for using FixYa.com

Posted on Oct 08, 2010

  • A Miller Dec 07, 2010

    You could replace the control switch ... one of the shelf at the ACE or other fine hardware retailer shold work ... You will of course have to set the switch for the proper pressures. The instructions should come with the switch.

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  • Master
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There is a rubber seal at the base of that valve that is likely worn.

Disperse pressure before working on it.

What is the model #?

Should be something like xxx . xxxxx

Thanks!!

Posted on Oct 08, 2010

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  • Master
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Hi Michael. Thanks for choosing fixya! That needle valve may just need a little lubrication. Get a can of WD-40 and squiirt a little on the valve. Move the needle up and down as you squirt it. Repeat as needed. IF this does not do it, you will have to replace the valve. It is available at searspartsdirect.com

Please give my answer 4 thumbs up. Thanks. Joe

Posted on Oct 06, 2010

  • Joe Hogan Oct 08, 2010

    Hello again. go to searspartsdirect.com, enter your model number and you will see an excellent set of schematics for your compressor. order a new part and install it. Joe

  • Joe Hogan Oct 08, 2010

    Hello again. I just got the updates on your repair discussion. As you now know, Sears and Craftsman only maintain a parts inventory for ten years. After that, finding parts becomes doing just what you said, a "hunt". Actually the part is common, it is just finding one that will fit your app. That said, I would consider checking on Craigslist.com. Often they have used tools and you may just find a duplicate for little money which you could use as a parts source. Joe

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