I have a Makita AC640 compressor which seems to be doing something odd, or as it's my first one maybe I'm doing something odd?! The pressure builds but does not cut out once desired pressure is reached (set on the smaller guage at only about 25 - 30psi) and air is eventually expelled via the safety release valve. This cycle continues throughout use. Very occassionally since I've had it, the machine cuts out as expected once pressure is achieved, and only starts up again when the gun has been fired a few times. Could it be a faulty guage/valve/other? Any help much appreciated.
Compressor pressure release
- Thread starter Bredbin
- Start date
Help Support UKworkshop.co.uk:
DaveL
Established Member
Hi Bredbin,
Welcome to the forum.
I don't have the same compressor as you but looking at the pictures and spec on screwfix:
The way these work is to pump the tank to a pressure higher than required and the supply air via a regulator at the correct pressure. From the spec the tank should be pumped up to 116psi, you then set 30psi on the output.
What should happen is the automatic pressure switch (the black box with the red knob/button on) should stop the motor when 116psi is reached. You use air from the tank and when its dropped by say 10psi the motor is started again. There will be a safety valve to release the pressure if the switch sticks and does not shut of the motor.
So when the safety valve opens what pressure does the tank gauge show? It could be that the switch is set too high, or the valve is set too low. It could be that the switch is faulty and if its a new bit of kit you should be taking it back under guarantee.
Welcome to the forum.
I don't have the same compressor as you but looking at the pictures and spec on screwfix:
It looks a useful little machine. 8)
The way these work is to pump the tank to a pressure higher than required and the supply air via a regulator at the correct pressure. From the spec the tank should be pumped up to 116psi, you then set 30psi on the output.
What should happen is the automatic pressure switch (the black box with the red knob/button on) should stop the motor when 116psi is reached. You use air from the tank and when its dropped by say 10psi the motor is started again. There will be a safety valve to release the pressure if the switch sticks and does not shut of the motor.
So when the safety valve opens what pressure does the tank gauge show? It could be that the switch is set too high, or the valve is set too low. It could be that the switch is faulty and if its a new bit of kit you should be taking it back under guarantee.
Newbie_Neil
Established Member
Hi Bredbin
Welcome to the forum.
Cheers
Neil
Welcome to the forum.
Cheers
Neil
Thanks for the advice Dave.
The main dial gets to around the 116 mark before pressure is released. Secondary dial is set to 30 psi. The black box/red button assembly has no settings - it's just a black box with a red button!! So it seems to be a fault - as you say the motor should cut out at 116 psi rather than the pressure be released through the safety valve.
I guess I will have to try my local Makita supplier.
Cheers
Paul
The main dial gets to around the 116 mark before pressure is released. Secondary dial is set to 30 psi. The black box/red button assembly has no settings - it's just a black box with a red button!! So it seems to be a fault - as you say the motor should cut out at 116 psi rather than the pressure be released through the safety valve.
I guess I will have to try my local Makita supplier.
Cheers
Paul
OLD
Established Member
As i understand it the safety valve is blowing of at to low pressure so it beats the differential switch to the cut off point so a new valve or adjustment should fix it .
Is it still under warranty they just need the original invoice.
Is it still under warranty they just need the original invoice.
Russell
Established Member
Please note many people forget to release the air from a compressor when you have finished using them. You must open the drain valve this lets nay air and more importantly moisture that builds up in the reservoir. In some units I have come across they have had 2 or 3 pints of water in the tanks because they haven't been drained. all it does is rust inside and weakened the tanks if its not drained and de pressurised after each use correctly
I can't see any adjustments on the switch or safety valve so it must simply be a fault.
Regarding releasing the pressure after use, I have always done this since getting it, if only for peace of mind - leaving a pressurised tank sitting around doesn't seem like a good idea!
Thanks for ideas.
Regarding releasing the pressure after use, I have always done this since getting it, if only for peace of mind - leaving a pressurised tank sitting around doesn't seem like a good idea!
Thanks for ideas.
davy_owen_88
Established Member
Hi Bredbin, its perfectly normal for a small amount of air to be released when the upper pressure limit is released and the motor turns off. This is just a small amount of excess air that was pumped in before the motor switched off and causes the valve to release it.
Hope this helps and I haven't totally missed your point..
Davy
Hope this helps and I haven't totally missed your point..
Davy
Thanks Davy, but the problem is that the pressure is released at the upper limit but the motor doesn't switch off. It just keeps going till the upper limit is reached again, pressure released, and keeps going like this until you manually switch it off.
Cheers anyway
Cheers anyway
I have found out how to rectify this problem - may be of use to any of you with the same model or similar.
I spoke to technical support at Makita today - this is not in any instruction leaflet that I have but if you unscrew the black box that the red on/off knob is mounted on, there is a bolt underneath marked nearby with plus/minus indicators. I just needed to turn this in the minus direction a few turns and the motor now cuts out when correct pressure is reached. I think with the motor running the vibrations may possibly over time cause this bolt to rotate and so adjustments may be needed occassionally. Anyway all is working now and not so noisy!
Hope this helps.
I spoke to technical support at Makita today - this is not in any instruction leaflet that I have but if you unscrew the black box that the red on/off knob is mounted on, there is a bolt underneath marked nearby with plus/minus indicators. I just needed to turn this in the minus direction a few turns and the motor now cuts out when correct pressure is reached. I think with the motor running the vibrations may possibly over time cause this bolt to rotate and so adjustments may be needed occassionally. Anyway all is working now and not so noisy!
Hope this helps.
Ed
Established Member
Hi Bredbin,
The plastic cover with the big red button can be removed by taking out the single screw on the top.
When inside you should see an adjustment bolt that can be used to adjust the cut off pressure at which the motor stops. From memory it may even have + and - markings stamped in the metal cage to indicate which way to turn it.
You should be able to adjust this so your motor stops just before you hit 116psi. This is assuming that it's just out of adjustment and not faulty.
If you need a photo I can dig one out as I have some in bits down the garage somewhere.
When it's working properly the it should reach 116psi and the motor turns off with a quick release of air. The release of air is from the little black pipe that runs from the pressure switch to the one way valve at the other end of the tank. This basically releases the pressure in the copper tube between the pump and the tank so that when it restarts the pump motor does not have to overcome that resistance to get spinning. (Thats also the reason why you should use the red button to turn it on and off as the button also operates the dump valve).
If the adjustment does not work and your out of warranty I can probably find you a spare switch (no plastic cover though) in the junk in my garage.
Cheers
Ed
The plastic cover with the big red button can be removed by taking out the single screw on the top.
When inside you should see an adjustment bolt that can be used to adjust the cut off pressure at which the motor stops. From memory it may even have + and - markings stamped in the metal cage to indicate which way to turn it.
You should be able to adjust this so your motor stops just before you hit 116psi. This is assuming that it's just out of adjustment and not faulty.
If you need a photo I can dig one out as I have some in bits down the garage somewhere.
When it's working properly the it should reach 116psi and the motor turns off with a quick release of air. The release of air is from the little black pipe that runs from the pressure switch to the one way valve at the other end of the tank. This basically releases the pressure in the copper tube between the pump and the tank so that when it restarts the pump motor does not have to overcome that resistance to get spinning. (Thats also the reason why you should use the red button to turn it on and off as the button also operates the dump valve).
If the adjustment does not work and your out of warranty I can probably find you a spare switch (no plastic cover though) in the junk in my garage.
Cheers
Ed
Ed
Established Member
Bredbin,
With my longwinded slow typing and having a cup of tea you got there before me. Glad its fixed
Ed
With my longwinded slow typing and having a cup of tea you got there before me. Glad its fixed
Ed
