When the pressure reaches 125 it will not turn off.but there is a small valve with a small black hose in the top of it and you can push up underneit and the compressor will stop. thanks for your quick reply and answer. don
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Re: compressor will not turn off
Most single stage compressors come with a pressure switch set to shut off at 125 - 145 psi. These switches become less efficient over time and will Begin to fail but remain useful. A safety valve (brass plut with pull ring) is installed somewhere on your compressor set to open at aprox. 160psi. If the pressure switch shuts off before the safety valve activates you could probably continue to use the unit. If however you would like to have the unit shut off at 125psi replace the switch any switch that can be installed in the space allowed. The black tubing that you see is the unloader. When the unit reaches set pressure and shuts off, the small valve under the pressure switch will open and release the pressure in the tubing. This allowes the compressor to start with no back-pressure. For max. life of compressor make sure that there are no leaks in system and upplug when not in use.
Pressure switches are sold in pressure ranges from 45psi to 160psi. Some brands are better constructed than others. A squareD switch will give long life being used w/o extension cord. Good Luck
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The maximum pressure on most small compressors is 10 bar or 1000kpa which is about 145 psi in the old language most safety valves are set to 150 psi. I suggest you get some one to reduce the pressure switch setting. Running a compressor at elevated pressures does not give you any more air. A reasonable pressure for small compressors is 120 psi
Check the pressure switch. The unloader valve is actually in the pressure switch where the small air line from the tank check valve attaches to it. When the pressure switch turns the motor off it then lets the head pressure bleed off so the motor can restart the next time pressure drops in the tank. If it's not working and bleeding off the head pressure the cold start valve (the one with the pin in it) also won't open so the motor can restart and warn up properly.
If your compressor is oil-less type, most likely pressure is leaking past piston ring. To verify, remove cover to expose bottom of cylinder (unplug compressor and let out all air). With flashlight, examine the upper-most part of the cylinder (turn motor by hand till piston is at top of stroke). If top of cylinder is scratched, then pressure is leaking past. For many years now, stores are in a race to have more HP and PSI to attract customers. Customer is really the loser because components used to make the units can not handle the higher pressure. Normally small 115v compressors are set to cut out at 125psi and larger two stage units will cut out at 160psi. Small compressor set to 200psi makes for short lived compressor. Could be compared to driving your car at 100mph all day every day. Longest life is attained when unit is being used at about 60 to 75 % of capacity. To allow your compressor to reach cutout pressure and keep working for a while, lower cutout to 120psi (pressure switch may be adjustable). To restore to 200psi, replace cylinder/ ring. If your compressor is oil type, suspect leaking reed valves.
Your infeed valve is stuck/broke in the open position. As you are looking at the motor/pump side of the compressor, on the right side of the top tank there is a brass valve that has leading into it a copper tube from the pump and the small black tube from the pressure switch. This valve lets air into the tank from the pump but should close when the pump turns off. When the motor turns off the black tube lets air bleed out of the pump and copper line so the motor can turn over when the pressure switch turns it on again. You need to contact Hitachi or one of their service centers to find out which infeed valve you need, they ahve different part numbers depending on what year your compressor was made. Go to http://www.hitachipowertools.com/index.aspx and use either their contact us page or the search for your nearest service center page and they should be able to tell you what part number you need.
Hi, I suspect the plunger for the valve stem connector on the pressure head is not depressing the air release pin in the head of the valve stem.
I have a Black and Decker and have to use a valve stem seat removal tool to quicky unscrew about 3 to 4 turns the stem seal and then connect the air hose head. After the tire reaches the correct air pressure I have go thru the tighten the valve stem seat drill.
You can buy the vavle stem seat tool at any auto parts store. I keep mine with the compressor.
I don't want this to sound bad but... is the air hose supply vavle turned on? Some have a slider button on the valve you have to push to charge the hose. If the hose is charged then see above.
Generally, the safety/relief is set to 140 to 160psi. The pressure setting is stamped on the side of the valve. Replace the valve if it will not hold stamped pressure(cost about $6 at Lowes Lumber).The pressure switch is usually set at the factory to 120 - 130 psi. The unloader part of the pressure switch will not release backpressure unless it reaches set cut-off. The 1/4 inch line attached to the pressure switch connects to air discharge tube at the intank checkvalve (brass valve). The safety valve should very rarely release pressure, only when pressure switch malfunctions and allows pressure to reach up to 160psi. The tank will hold over 300psi so dont worry about the 160psi safety. I am not sure about your exact model number or brand, however most small compressors work the same and share similar parts. For manuals to other similar compessors to to www.dewalt.com. Here you will find manuals to dewalt and porter cable compressors. I prefer to use generic replacement parts from www.grainger.com or from Lowes Lumber. These parts will cost less than factory replacement. If you need to replace the pressure switch, use SquareD brand from grainger. Watch fitting sizes and pressure range. Good Luck on your repair.
I have worked on many makitacompressors and have run-across this problem on a few of them. Your compressor has a check valve that is supposed to hold tank pressure after the switch reaches set pressure. There is an unloader valve built into the pressure switch that releases the pressure in the discharge hose after the unit shuts off. The unloaderallows the compressor to restart with-out any pressure in the discharge line. If the brass check valve is leaking pressure back into the system, air will leak out of the unloader valve. Follow the discharge line to the tank and you will see the brass check valve. To test valve for fault, run the compressor till it builds around 80 psi and unplug the unit from the wall outlet. Remove the 1/4" hose connector from the check valve and check for air leaking out of the valve. If it is leaking you can order form www.toolpartsdirect.com. or call the makita 1-800 number. The price is about the same. Good Luck on your repair.
The non-return valve is sticking and it's an easy fix. First, for safety, unplug the electric power to the unit and release any pressure in the tanks. Then unscrew the cap of the non-return valve (between the compressor and the tanks). Inside you should find a tapered rubber plug which is probably sticking in the valve housing. Sand down the diameter of the large end of the plug, being careful not to damage the flat face at the narrow end (which is the sealing surface). For sanding try 400 or 600 grade wet-or-dry paper and sand until the plug just moves freely in the housing. Reassemble and the compressor should work. Incidentally it's an oil-type unit, and quite durable. Make sure it has enough oil.