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Spray gun problems, please help

I have an Iwata LPH 440 and it is leaking air out from behind the trigger. I have replaced about everything and it still leaks air. The brass piece, plastic piece ahead of it, steel piece ahead of that and the fluid packing seat as well. I have 3 sets of needles and all leak. AM I missing a piece or...?

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Sometimes you have to snug up the nut behind the trigger to make a better seal, too tight and the trigger gets harder to pull and it wont release loosen it till it pushes on the trigger again.
The one that the fluid adjuster screws into? Or the plastic one?

This is driving me nuts, I've rebuilt my other 2 Iwatas with no issues. About ready to send it somewhere.
The one that the needle goes through just in front of the trigger. Tighten it until the needle won't move and then back off just enough to allow smooth motion.
This is where a tiny bit of grease is normally applied.

ps If you decide to send it some where, I'll give my address!
I don't believe that's where the airflow is coming from but I'll try it again. It seems like air is coming from behind the trigger. I have been using air gun assembly lube on everything. While air is leaking, I have had the nut ahead of the trigger both loose and tight, it leaks no matter which way. The packing nut is new as well.
It seems like it's leaking past part number 12. I have replaced 3, 6, 7,8, and 12. I have used lubricant on all the o-rings during assembly.

There shouldn't be any air getting to the front of the needle/packing nut/air cap area until the trigger is pulled, right? It seems to me like air should be stopped by part number 7 until the trigger is pulled back, but I'm not sure either. Pull the trigger and it presses on 12, which pushes back 7 opening air flow into the the fan valve and then to the air cap...right?

So if I have air leaking when the trigger isn't pulled.... I don't know. I'm lost. Maybe I'll take a video or something. anest_iwata_lph440_primer.png


Registered Users
Have you checked where air hose/regulator connects to bottom of spray gun? Sometimes the swivel area wears and air comes thru even tho it's tight and not able to move.
Yes, it's not leaking there. I just swapped a bunch of parts from the 400 to the 440 and it got somewhat better but still leaks. It has a small leak letting air into the fluid nozzle (2-1), a small leak around the packing nut (3), and a small leak around the air valve shaft (12). If I lightly press back on the air valve shaft (12) then the packing nut leak and fluid nozzle leak stop. If I press forward on the air valve shaft (12) until it's against the trigger, then it's own leak stops. Seems to me like the air valve seat (7) isn't sealing allowing air to get around it and leak through to the nozzle/tip area. I don't think the packing nut is leaking once it gets moved the slightest amount, possible a worn needle in that area?

Is the air valve shaft (12) supposed to be constantly pressed against the trigger?


Registered Users
I've got a 400 lph orange cap. I'll look when I go to shop later today. If we could only color the air so we would know where it's coming from.


Registered Users
After watching video it seems like you were right air valve not sealing. Either seal or worn needle my guess. I'll look at mine later today.
And even if the needle is worn, no air should be getting by the air valve seat (7) until the trigger is pulled far enough for the air valve shaft (12) to push it back and allow air to pass through....right?
I suppose if you were gonna break it down again, couple drops of uv dye & uv light certainly would find it.
I never did this other then drawing on a ex gf with marker & black light on but it glowed :)
It is completely broken down again. I'm going to soak it and my 400 while I get a couple seals and a good brush kit for cleaning. Use my LPH 80 for now, I'm just painting some gas pump parts. More than anything it's bothering me that I can't figure it out. I did notice that my 400 air valve parts seem to be smoother, but they are older so they may just be worn in. I noticed my 440 needles are all scratched in the same spot, and it's in the air valve area. Not sure if something was crooked or overtightened or what. Luckily, it shares needles with the 400 so I have a spare.
I polished stainless bolts to use as axles on my home brew pool wheelchair.
Chucked them in drill, pinched them with different grits of paper till perfect.
Then spun them pinched with rag & metal polish. Came out like chrome.
I may have figured it out. Apparently there is packing inside of the fluid adjustment guide nut (9). That may be the problem. Unfortunately you have to buy the entire nut. I will have nearly $100 into this thing... ugh...

It is my own fault in the end. I had been soaking this part and I'm sure it's not mean to have the packing soaked. Had I known there was packing inside, I would not have soaked it. Live & learn... well.... if this is the problem!
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Video post was cool, that's one up on me for sure, I sure don't know now to do that, hell I still use a flip phone.....

Like it was asked, keep us updated to the issue. With all the sealing washers and parts it does make it kind of a crap shoot to narrow down.