# Graco 390 pressure issue



## Philippe_T (Jun 11, 2018)

Hi,

I need help figuring out what is wrong with a Graco 390.

I cannot adjust the pressure. If I adjust the pressure via the knob it will either keep the pump running or if I lower the pressure it will stop the pump. If I press on the gun it will release the pressure but the pump wont start.

Also, in prime mode, sometimes I can have a niceflow but sometimes I can't get any flow. Would it be time for a packing replacement?

I have never used it for so far. I'm trying to get this used sprayer a go.

Thanks
Phil


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## Philippe_T (Jun 11, 2018)

I took the unit apart and I'm wondering how the pressure is controlled?

Is it a fixed speed unit from a pressure Switch On/Off? or does it regulate its speed from a pressure feedback?

Thanks


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## cocomonkeynuts (Apr 14, 2017)

Philippe_T said:


> I took the unit apart and I'm wondering how the pressure is controlled?
> 
> Is it a fixed speed unit from a pressure Switch On/Off? or does it regulate its speed from a pressure feedback?
> 
> Thanks



Yes it uses a transducer feedback


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## Philippe_T (Jun 11, 2018)

Ok, because when I look at it it seems to be a membrane that support what your are saying but I do not get why the adjustement would be on top of it? It's only a two wire setup. So to me it looks like an on/off switch feedback.

Also, I took the unit apart and it is missing the inlet ball and seat. I will replaced those and test back.

Was it normal for the hose to move while it was pressurizing? I don't have a gauge so I don't know if I was near the setpoint or not.


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