SM 11 the back pressure Error is preventing me from starting

by Josh

SM 11
SM 11 gauge closeup
SM 11 air compressor

_____________________________SM 11 gauge and plumbing

Fault code
by: Carl

Actually, thinking about it, i cant see the number on the bottom line of the screen? What number or letter is it showing when you turn the power on?


by: Carl

Hi again,
Thanks for the photo. Sorry, i may have misunderstood, it looks like, as you said, the back pressure fault is as soon as you turn the power on, not when you press the start button. I can see on the screen of your Sigma basic controller the bottom line is illuminated.
Does it let you reset this by pressing the reset button (reset button is the red “Stop” button) if if it doesnt let you reset then i havnt seen that before, are all the electrical connections in properly? The connection into your vent valve? (Brass component attached to the separator with a hose going to the air filter) if all these connections are ok then you may have a problem with the controller itself which could mean you may need an HPC engineer to come along to look at it to “K-load” it which mean taking all software off and putting back on again. Or a new controller.
Let me know how you get on


by: Carl

Im guessing you have a sigma 1 controller fitted and it has the words “back pressure” on the screen as opposed to a number on the bottom row of the screen as you would with a sigma basic controller?

Either way, the back pressure error is indicating that you have pressure in the separator tank (where the oil is).

Do you have a pressure gauge on this tank? If so then it should read zero on start up.

Attached to the separator tank is a combination vent valve where you should find a little ball valve which is used for keeping pressure in this tank and firing out the oil when you have an oil change.

Check that this valve is open or you will get the back pressure error.

Secondly, inside that brass vent valve i mentioned is a rubber diaphragm, it has been known for this to inflate so will not let the separator vent, replace the diaphragm (it comes in an intermediate service kit along with air filter, oil filter and filter mat)

Finally, again with the vent valve, do you have an electrical connection to it? Make sure you have voltage going to it?

How old is your machine? If you could post a few photos of the machine and the vent valve/separator it would help a great deal.

Try all the above and reply to this post to let me know if it fixes it.

Many Thanks


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