- Thread starter s410man
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rtbcomp
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The small one , especially if it has a triangle marking near to it.
Adjusting one screw will affect the setting of the other, so keep checking both of them. Some pressure switches should only be adjusted if there is pressure in the tank.
I don't like the look of the wiring - he's used a blue conductor to carry a live and the earth is disconnected - could do better! I'd rewire it to work as a double pole switch too.
Adjusting one screw will affect the setting of the other, so keep checking both of them. Some pressure switches should only be adjusted if there is pressure in the tank.
I don't like the look of the wiring - he's used a blue conductor to carry a live and the earth is disconnected - could do better! I'd rewire it to work as a double pole switch too.
which means?
brightspark
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its probably been wired back in to a contact starter hence only using 2 wires so the pressure switch only operates the contactor coil not the full load current of the motor as in the cheapo new ones . the eath should be conected but the colour of the cable doesnt matter but the blue should be sleeved to identify it as a switched live either end
As you say the big screw on the right is the pressure cut off and the small one on the left is the differential, turn the diff screw in the - direction. it looks like a danfoss switch does it have an unloader underneath the switch and is pressure reliving out of it when it switches off when up to pressure.
rtbcomp
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I wondered about that, perhaps it's been wired incorrectly and the contactor is working like a no volts release ??
S410 man - if it doesn't restart automatically, how do you get it to restart?
press the on button
rtbcomp
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Sounds something like the on button is a no-volts release (NVR) and is wired after the pressure switch.
When the pressure switch opens the NVR cuts out and the button has to be pressed to restart.
Could we have some pics of the start button and any other electrical gubbins on the machine.
When the pressure switch opens the NVR cuts out and the button has to be pressed to restart.
Could we have some pics of the start button and any other electrical gubbins on the machine.
![20121208_185721[1].jpg](/forum/data/attachments/28/28838-aef6e68c17da6bcb99533f0dc4521b2a.jpg?hash=rvbmjBfaa8)
rtbcomp
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When it reaches cut-off pressure do you hear a distinct hiss, and how much do you let the pressure drop before restarting it?
There appears to be an over-current trip in there (the green knob), if that is cutting out as the load on the motor increases with pressure then it will stop without a hiss, and pressing the on button will reset the trip.
What size motor is it?
Can you tell what the over-load trip is set to?
There appears to be an over-current trip in there (the green knob), if that is cutting out as the load on the motor increases with pressure then it will stop without a hiss, and pressing the on button will reset the trip.
What size motor is it?
Can you tell what the over-load trip is set to?
![20121209_115706[1].jpg](/forum/data/attachments/28/28839-25071cba59b1dd1b78a72c153c2d56a6.jpg?hash=JQcculmx3R)
![20121209_115813[2].jpg](/forum/data/attachments/28/28840-b7bf0de812dc20e0aa1c546c8dce57a7.jpg?hash=t78N6BLcIO)
![20121209_115726[2].jpg](/forum/data/attachments/28/28841-4a57ae4bb263a6dfff85446141841fe9.jpg?hash=SleuS7Jjpt)
![20121209_115754[2].jpg](/forum/data/attachments/28/28842-69b94e42e97a9fb9bdf578f64076d929.jpg?hash=ablOQul6n7)
the artfull-codger
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Looks like the old Danfoss pressure switch which just cuts out & then back in at the pressures you set it to, mine drove a contactor so no real amperage involved,the downside is it doesn,t unload the pressure when stopping so your compressor's starting up under a load,depending on what it's set to,I replaced mine with one off ebay[cheap as chips] about £12.00 & when it cuts out you hear it hiss as it unloads the pressure in the supply pipe ready to re-start without load.
slan go fol
slan go fol
rtbcomp
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Yes - the hiss is important!
There's definitely a coil in that big switch box, and it looks like one of the wires from the pressure switch connects to it. I guess it's a NVR problem I mentioned earlier, the pressure switch must be OK if it allows the pump to restart via the on button after the pressure has dropped.
S410man - is there a thin pipe from where the pump connects to the tank going back to either the pressure switch or the switch-box? Also watch the gubbins inside the switch-box, does something move when the motor cuts out?
I understand some compressors have a centrifugal unloader in the pump itself, don't know whether or not you get a hiss from that type.
There's definitely a coil in that big switch box, and it looks like one of the wires from the pressure switch connects to it. I guess it's a NVR problem I mentioned earlier, the pressure switch must be OK if it allows the pump to restart via the on button after the pressure has dropped.
S410man - is there a thin pipe from where the pump connects to the tank going back to either the pressure switch or the switch-box? Also watch the gubbins inside the switch-box, does something move when the motor cuts out?
I understand some compressors have a centrifugal unloader in the pump itself, don't know whether or not you get a hiss from that type.
Things are a little clearer now with these pics, the pressure switch as artfull codger said is the one without an unloader fitted, that pressure switch was only rated to run a 1.5 hp motor directly on single phase, the MEM auto-memota is also rated for 8 amp, So what is the actual horse power of the electric motor thats on it.
Clearly the previous owner has replaced the pump because the old was shot but has not taken into account how its supposed to unload when up to pressure. you at the least need a new pressure switch, you might also need a non return valve, there might be an in-tank one fitted but you would have to take it apart to check if there is one fitted you can tee off to unload the discharge side through the new switch. that is assuming if the electric motor is man enough to run the compressor.
Clearly the previous owner has replaced the pump because the old was shot but has not taken into account how its supposed to unload when up to pressure. you at the least need a new pressure switch, you might also need a non return valve, there might be an in-tank one fitted but you would have to take it apart to check if there is one fitted you can tee off to unload the discharge side through the new switch. that is assuming if the electric motor is man enough to run the compressor.
I'd fit a new motor and tank as well
Well hey big spender
you come into money or something.
brightspark
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i had the same setup with a 2hp old motor same as that one it didnt need an unloader and started up nicely at 90psi without one 
it was 30 year old. i had to put a new one on same size and it cant pull the skin of a rice pudding and will need an unloader. ask the op what hp or how many amps the motor is on its id plate. that tank and motor will outlast even the new ones as they were built to last
it was 30 year old. i had to put a new one on same size and it cant pull the skin of a rice pudding and will need an unloader. ask the op what hp or how many amps the motor is on its id plate. that tank and motor will outlast even the new ones as they were built to last 