Blow back

Germanjim

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Jimbob
#1
I'm at my wits end with this, I have a lwata hp-b plus using it today I couldn't get the airbrush cleaner through it never mind paint. Finally giving in I completely dismantled it gave it a thorough clean re assembled it but still had the cleaner bubbling in the cup. I have tried everything I could but it still refuses to spray. So any ideas will be welcomed especially as one of the models is needed in 2 weeks time.
 

col68

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colin
#2
Jim have you checked that the needle isn't bent or the fluid tip isn't deformed.
The only other thing I can't think of is that the needle isn't travelling back far enough, one of the seals in my old devilbiss let paint leak into the body and it stopped the needle moving back properly.
 

Germanjim

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#3
I have examined the needle and the tip under the magnifier and both are fine I've tried everything bar removing everything from the body of the brush which I don't like doing.
 

Tony

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#4
Its difficult to know what might be causing the issue but maybe the following deep cleaning guide may help.

If the brush is clean then it does sound like a seal problem.

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There are also some trouble shooting tips towards the end of the following link

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Last edited:

m1ks

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#5
Double check your nozzle for splits, easiest way is to take off the fan cap and needle cap then view it through a loupe or magnifier as you gently seat the needle and withdraw it (by hand with the chucking nut loose), a split that's not visible with the nozzle removed will become evident and it only needs the tiniest to do what you describe.
Other possibilities are a bent needle tip or blocked nozzle.
The reason it's happening is that air is being forced back into the paint cup via the nozzle or the nozzle seal (so the nozzle to body seal is a possibility) and this shouldn't be able to occur if the needle seals properly against the nozzle opening.
 

stona

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#6
Not familiar with that particular brush, but if you are sure that the nozzle itself is fine and correctly fitted, and the airways to it are clear, then the nozzle cap seal to the body would be my prime suspect.

Cheers

Steve
 

Germanjim

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#7
Thanks guys will leave it to the side for a while and use my other iwata's thinking of buying a H&S infinity soon anyway.