Question about Dewalt 2 Hp 4 GAL Air Compressor

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Not building pressure into tank

I have removed pump from tank and checked out but maybe needs rebuild kit. Wondering how do the reed valves work

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  • Anonymous Jan 27, 2009

    same problem

  • TechTrainer May 11, 2010

    when you turned on the compressor was the motor and pump working and the tank just not holding air?

    just making sure it wasnt something simple that you wouldn't have had to tear off the pump.



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If it's a newer model the parts are surprisingly inexpensive in some cases. Locate the parts and you may be surprised, I know I was a few times replacing whole piston assembly for almost just a few bucks and so quick and hassle free. And that fixed the no air into the tank issue I had on the job back up and running in an hour counting going to get parts.If it's oill free that's what I had, very inexpensive and easy just replace the piston assemblies undo the rod and it should drop right out the bottom.

Posted on Nov 20, 2008


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If you aren't getting a buildup of air in the tank, either the tank isn't holding the compressed air or the pump isn't compressing air. Check the unit for leaks, especially at all joints like the tank drain valve, pressure switch, tank check valve and the pressure relief & outlet tubes. If all of these are OK, you'll have to check the pump. Remove the head to check the condition of the valve plate and reed valves. Also check the piston ring and cylinder for damage. You can go to a site like to see a great breakdown of your compressor. Most parts you may need are also available there.

Nov 18, 2012 | Porter Cable Cable Brad Nailer and...

1 Answer

I have a husky scout 1.5 gallon air compressor. It only builds pressure to about 38 psi. It doesn't build up any more pressure.

You have either warped or broken reed valves on the valve plate or a broken piston ring and/or a damaged cylinder. Any of these will allow a small amount of air compression but as the tank gets pressure in it, it gets harder to push more air into it. If the reed valves or piston to cylinder seal is compromised more and more air will leak past the bad reed or the piston as the pressure goes up in the tank. You'll have to disassemble the air pump to find out what's damaged and needs replacing.

Mar 03, 2012 | Air Tools & Compressors

1 Answer

Engine runs, but stopped pushing water

First I would start with the simple solutions.1. Check to see if your water pressure is good. 2. Check the pressure hose and tip for ubstructions. 3. Check the inet strainer and make sure you have no leaks. 4. Check the unloader valve which is located usually in the area of the pipe for your pressure hose connection. Remove and clean valve and port the valve sits in and lube with white lithium grease light coating. Try machine, if this doesn't work remove pump and inspect all the check valves and pump body for build up of gunk. If you find this you can clean with carburetor cleaner or you may have to purchase a rebuild kit. If you have problems finding the unloader valve go to and do a parts look up and you will see where this valve is. You can also purchase the rebuild kit on this site. Hope this helps.

Jul 24, 2011 | Karcher 2500 PSI Pressure Washer

1 Answer

Compressor goes to 35 psi wont fill anymore

There are a number of possibilities. The head on the compressor pumps usually uses some type of reed valves to separate the intake and exhaust sides. You can remove the top bolts (usually 4 bolts) that hold the head on and inspect the valve plate(s). Are the reed valves (usually just small metal strips) broken or not seating on their plates. Are the gaskets in fine shape? If you get a tear in the middle of the head or valve plate gasket, where it separates the intake and exhaust, then the pump will only build up pressure to the range you have or sometimes up to only the 50psi range.

Another thing to check is if it has a one way check valve that goes into the tank where the pump line/hose feeds from the compressor pump into the tank. Many of the check valves use a simple plastic cup and a spring. If they get stuck open then that will also make it not build up pressure.

The other part I can think of is the control box but usually when they fail they either won't turn on the unit or they will leak air.

The last thing to check would be the piston ring(s) and cylinder/sleeve. The oil less compressors will wear these items out far more often then an oil style will. When the oil less piston and sleeve get scored up (from dirt ingestion) then they also will not build up much pressure.

Jul 20, 2011 | Craftsman 3 gal. Air Compressor, 1 hp,...

1 Answer

Compressor squeaks as pressure begins to build. Not from belt. Does not squeak when no pressure in tank.

Air leaking back from tank check valve or leaking reed valves can make a squeaking or vibrating noise. With pressure in tank remove fitting at the tank check valve and test for leak with soapy water. If leaking, replace with generic valve. If no leak, reinstall fitting and let all the air out of the tank. With empty tank and air filter removed, start compressor and feel strength of suction at intake. When you hear the squeak retest strength of suction at intake and compare. If reed valves are leaking, you will feel less suction as tank pressure increases, and in severe leaking valves, you will actually feel air blowing out of intake. Repair/replace reeds and /or leaking gaskets in head of compressor. Good luck

Mar 08, 2011 | Ingersoll Rand IngersollRand SS3F2GM...

1 Answer

Will not build pressure past 40 psi

You have either damaged reed valves or piston ring. Both of which are common problems with this type of compressor. To diagnose: Remove the motor cover, then the four screws holding the cylinder head on. The valve plate is under the head and all eight reeds, five intake and three output, must be in very good condition to work properly. You'll need the valve plate, part number N017592, and head gasket, part number Z-D24819, if there are any damaged reed valves. If they're OK, check the piston ring. Remove the screw holding the piston on the flywheel and pull the con-rod out of the cylinder. The ring around the piston must be in perfect condition to build pressure. The connecting rod kit, part number KK-4964, is the only way to get the piston seal ring.

Jan 17, 2011 | Porter Cable C2002 150 Psi 6 Gal...

1 Answer

Will not build pressure. It's as if the check valve is stuck open. Where is the check valve and how do I check it.

Easy to check. Follow discharge air tube from compressor to the tank. The brass valve that the tube attaches to is the check valve. You will need some air in the tank for the test. Remove the discharge air tube at tank and spray soapy water. If leaking replace valve or remove and attempt to clean debris. Does not sound like your problem is the valve however. If no leak at valve, check reed valves or head gasket. If your pump is dry lube type, check cylinder for wear / scratches close to top of cylinder. Good luck

Sep 12, 2010 | Craftsman 3 gal. Air Compressor, 1.5 hp,...

4 Answers

Was working normal suddenly will not build pressure

Maurader1 an apprentice has this problem solved and is spot on. All these gurus and wiz need to stick to the basic and common sense. The first place your pump will give out after use or abuse is the gasket. All this garbage about defective reeds and defective pressure switch is a lot of nonesense if you first don't rule out the most common problem the head gasket. I'm cheap and this thing has paid for itself 10 time over. You can get a gasket kit for $7, but I fabricated a gasket out of the back of my notebook and sprayed some gasket spray and been working like a charm ever since.

Sep 27, 2009 | Craftsman 3 gal. Air Compressor, 1.5 hp,...

2 Answers

Porter cable pancake unit blows air after shut off.

those have a reed valve set up you need to pull the head off and you will see two strips of metal that are usually held down with two small screws each the one on intake side most likely you could get a rebuild kit cheap it will only have new reed valves maybe new screws for them a leather ring and a head gasket

Mar 14, 2009 | Porter Cable 18 - Gauge Brad Nailer and...

1 Answer

Intermittent pressure building

The check valve is easy to test. All that you have to do is run the compressor till you have some pressure in the tank, 50 ~ 60 lbs will do, then remove the air discharge tube at the check valve installed in the tank (the brass valve). Spray soapy water into the valve. Tiny leak is ok, rapid leak replace valve with generic valve from . Most likely problem is worn cylinder or reed valves in the head. To check cylinder, unplug unit and (oilfree compressor) remove cover to expose the crank. Push the piston all the way up and check for scratches on the upper part of cylinder. If scratched, replace with kit# K-0650 available at If cylinder is smooth all the way up then problem should be the reedvalve plate in the head. The reeds could be held open with debris or broken. Clean or replace as needed. Good Luck and email if you have questions about the repair. (Oil in crankcase type compressor will not have cylinder problems)

Feb 25, 2009 | Porter Cable Air Tools & Compressors

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