When I take the trigger apart and then put it back in the same way it then leaks air. I have 4 guns and I have been carefully cleaning them. Each time I take the trigger parts out and clean them and reinstall them the gun then leaks from the trigger. I have been paying close attention and putting everything back the way it was.... What the heck is going on?

I've found over the years the least amount of times you can tear a spray gun completely apart the better. Usually a real good 'flushing' with lacquer thinner will suffice. I will take the air cap off and let it soak in thinner to dislodge any build up but other than that, I simply run thinner thru till it runs clear out the tip.

I also 'back flush' which involves having thinner in the cup and the air supply hose attached. the air pressure should be adjusted quite a bit lower than what you use for spraying paint.

Then you place a clean shop towel or rag over the air cap of the gun and pull the trigger. This forces air back into the paint cup 'back flushing' the gun. Then take the rag away from the cap and pull the trigger again to run thinner thru the gun the normal way.

IF you still want to tear the gun apart for cleaning you can hopefully get some idea with this video link;

Quick Easy Way to Clean HVLP Spray Gun

Hope this helps.

You will have to take the gun apart and change the rubber o-ring gasket for the trigger mechanism..Go to a Home Depot or other contractor outlet to get parts or info...The gasket actually keeps the air from leaking so it will nail.

Needs rebuild kit or if you have a source for orings just replace all the vinyl (gold /yellow/clear in color) with buna or black orings. There are two vinyl orings in the trigger valve (metal stem) that fail and cause machine gun effect or replace trigger valve complete. Air out the nose indicates weak oring contact between the body of the gun and the white plastic cylinder spacer and also the cylinder spacer and the cylinder. I suspect the orings between the cylinder spacer and the cylinder (actually installed on the cylinder) . Good luck

Replace the trigger

Remove the trigger and remove the nails, connect air. Try to determine if air is leaking from the outer edges of the valve or from the center when you move the pin. If from outer edge, remove roll pins that hold valve in the body of the gun. Apply air pressure to pop out the valve(use glove the catch the valve, it could come out with force). Examine the two outer orings of the valve for cuts and replace as needed. Clean the opening where the valve fits with 400 grit sandpaper to remove debris and check for worn areas. If clean, apply plenty of silicone paste lube on orings and opening and gently push valve back in. If it leaks from the center pin, you may have a defective valve. You could try to repair if you have access to orings. Remove valve, remove two retaining pins and take valve apart. Small orings on the center pin could be the problem. Good holidays

The trigger assy. will have to be taken apart to replace the seal on the stem. Be sure to check the trigger pin for smoothness where the seal has been sealing. Replace the trigger pin if worn or your new seal may leak.

Assuming that there are no leaks, remove head and pull headvalve. Look for fine scratches where oring contacts head. If there is a deep groove worn into head or scratched, sand with 400 grit paper to restore smooth surface. If badly worn replace head. Reinstall parts using silicone paste (looks like vaseline, sold at lowes in the plumbing department, used for faucet orings) )

A nail gun works on compressed air.
When you hook the air hose to the gun it fills a cylinder with air pressure.
When you pull the trigger. the cylinder pressure is released onto a firing pin that shoots the nail.
The air pressure line is also connected to the trigger and therefore the trigger has to be sealed.

When ever using a nail gun, you add a bit of gun oil in the back of the gun (not 3-in-1motor oil, it has to be non-detergent gun oil)

If you haven't used the gun in a while, it is best to oil up the gun and let the oil run down into the gun.
If you use anything but gun oil, the seals will give out.

Your trigger seal has given out. It is probably an 'O' ring. You can access it by taking it apart. Look for the O ring.
Bostich makes re-build kits for the different guns that you can buy on-line.
Back when I was in construction, there were several nail gun shops that sold and serviced nail guns, and sold nails to the contractors. I don't know if that business model is still active or if you have to send the guns to Bostich service center.

if you took the trigger apart the part that you unscrew has a nylon ball and a black rubber ring you should check them and make sure that you didn't loose them when you took it apart,if they are there, then you need to service the gun, and after you clean all the moving part and you put it back together, it may still leak from the top,Take a rubber hammer and give it a good hit,now not to hard, and it should seal

couple of things there are o-rings inside that trigger assy. they are either pintched in or dry. next there could be internal rubber hoses inside the gun. might need replacing. lastly the hose or o-ring going to the back side of the ram is leaking or broken. here is what i would do. you sound pretty handy with your tools so i would get somewhere clean start taking the gun apart thouroghly noting where everything went and go untill you find the problem. but first i would shoot a couple of drops of oil into the air input on the gun then hook it up and fire a few off and see if it clears up, if not then start takeing it apart. I CAN NOT STRESS ENOUGH....DO THIS ON A CLEAN SERFACE WITH YOUR HAND CLEAN. i chased a leak around in a pnumatic hammer for 3 days all because it wasnt clean on the inside..