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Hi guys,
Apologies if this could be in another forum, but I have a technical question about spraying that perhaps someone can solve. The pressure on my gun drops immediately when I start a pass, and I can hardly go for even a couple of seconds before it's at zero. The pressure builds back after a few seconds, but then it's a repeat, repeat, inefficient and inaccurate spraying situation.

I've changed out so many things to try to find the culprit, namely isolated this line (put a disconnect to my car garage line), changed guns, changed the pressure regulator, tried bumping up the pressure in the tank (a large 80-gallon Craftsman), and at the regulator, and tried various adjustments at the gun.

What on earth could be causing the pressure to drop over just one or two seconds, then build back up just as fast?

Thanks for any ideas you can offer,
Ken

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Ken Mitchell
Durham, NC

first off
what kind of gun and brand
do you have a regulator on the gun?
all my guns have a regulator on the gun and I set them to the makers suggested settings Usually about 20lb
The large tank should be set about 160 psi
Do you have a water oil separator on the compressor if not get one
If you have a harbor freight gun get a real one I never had great results with them

So answer these questions and we can start your path in the right direction

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks for the list, John.

what kind of gun and brand one small Wood River, one cheap Harbor Freight unit
do you have a regulator on the gun? NO regulator on the gun, just a wall-mounted one
all my guns have a regulator on the gun and I set them to the makers suggested settings Usually about 20lb
The large tank should be set about 160 psi OK, maybe I need to bump that up; I thought 90-100# would be enough
Do you have a water oil separator on the compressor if not get one YES, built into the regulator
If you have a harbor freight gun get a real one I never had great results with them OK, good advice!

OK, from John's initial questions, it looks like maybe I should try bumping up the tank pressure. If that works, next I should get a 'real' spray gun!

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Ken Mitchell
Durham, NC

Set the regulator at the gun (and at the tank) with the trigger open. Make sure that your hose to the gun isn’t one of those thin plastic coiled hoses—they won’t pass enough volume. If those two things aren’t the issue, then it sounds like you have a kink or blockage somewhere between the tank and the gun. A small orifice somewhere will let the pressure build with no volume but won’t pass enough air to maintain the pressure when volume is needed.

If the pressure drop is shown on the gauge at the tank, then the obstruction is between the gauge and the tank. If it all worked before and not now, then some crud got into it and blocked it somewhere. What fun!

The length and size of the hose can also affect the pressure significantly, but it does sound like you have some sort of restriction between the gun and compressor. If you have an old compressor/ tank be careful if raising the pressure to 160psi. Moisture generated by compressing the air can rust and weaken the tank and the additional pressure can cause it to fail. 125psi is enough to run most air tools (many are made to work well at 90 psi).
If you have an air blower nozzle or other air tools do they behave the same way - a few seconds of hi pressure then quickly dropping off? What is the pressure you are setting the wall regulator to? If you are not regulating the pressure at the gun how do you compensate for the pressure loss in the hose? I use a cheap $5 HF regulator at the gun and don't even worry about what the dial indicates, I just adjust it where the gun sprays properly.

I think I may have found the main culprit. The output valve on the main tank had somehow gotten turned to a barely-open position. It's quite loose, and I've probably bumped it inadvertently a few times reaching around to the shut-off valve.

I'm going to try again this afternoon. As with many things, a small issue can cause major problems!

And yes, Clay, I don't usually go over 120# on the old tank (20 years of use).

I'll report back... fingers crossed.

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Ken Mitchell
Durham, NC

Wouldn’t it hiss loudly all the time if that were the problem? Just curious. Hope that’s all it is.

If you add a regulator at the gun, make sure it’s a regulator rather than a simple valve with a gauge.
The valve will drop pressure and also drop air volume.

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wah
Wah-wah-wah-wah
Wah

yes get one with a gauge and set it up with the trigger pulled don't just dial in 20 lb
there is a you tube channel you may want to sign up on call FINISH SOCIETY

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

These are the regulators I use at the gun. The price has increased since I last bought them but they are still pretty cheap. They work as a regulator not as something that just restricts the size of the air passage. I don't know how accurate they are with the gauge reading, but they do adjust the pressure fairly well. I adjust them to wherever the gun will spray properly and don't pay attention to the reading ( they may read fine - I just don't think about it)
https://www.harborfreight.com/125-psi-a ... 62695.html

I don’t think that is a regulator. It looks like a simple flow valve with a gauge.

_________________
wah
Wah-wah-wah-wah
Wah

I’m have this one which I *think* is a proper regulator.

https://www.amazon.com/DeVilbiss-HARG55 ... 75&sr=8-14

That being said, I’m going to try regulating the pressure at the source. I’m using a California Air Tools compressor and can set the output. Dan, I think you shared a while back this was a big improvement for you? I’m going to try the same thing next time I’m spraying. Thanks for the tip!


Sent from my iPhone using Tapatalk Pro

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I've shown this here before. It is the regulator I use on my gun. It is USA made and is a real regulator at an affordable price.

https://www.amazon.com/gp/product/B0073NVA2Y/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The reason you want a regulator on the gun is that it cancels out the pressure drop that is created in your air hose. A regulator on the air compressor will not give you accurate control of pressure at your gun.

https://www.amazon.com/dp/B07BW9BX6D?pd ... cefbda6bf0
this is one I use

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Like the one before, that LE LEMATEC is not a diaphragm type regulator but an orifice valve that restricts flow. So it does not hold a true limit on pressure.

Thanks to everyone for your input. It turns out that the main problem WAS indeed that the output valve on the tank had inadvertently gotten turned to where the pressure was almost completely turned off. As I sprayed, the pressure would quickly go down, then build back up in a couple of seconds. But... issue solved.

This HAS gotten me thinking about getting a better spray guy, though. I spray with WATER based finishes, and only spray 2-3 instruments per year, so I don't need the Cadillac or Ferrari spray guns. But I WOULD appreciate any recommendations on a mid-level, medium-sized spray gun, if people have favorite brands or types.

Thanks again for the help, and for any spray gun recommendations you may have!
Ken

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Ken Mitchell
Durham, NC

Some years ago when I could no longer get repair parts for my Asturo gun (whick I liked a lot), I called Jeff Jewitt at Homestead finishing and asked him for his recommendation. He sold me a Qualspray AM-5008P gun. I’m using the 1.3 mm tip. I spray EM6000 with it. It works very well. I am able to dial in a good spray pattern with it and lay down an even wet coat. I believe the gun is called an LVLP. It requires only 6 cfm. When I called Jeff, I thought I was going to upgrade to the top of the line Fuji turbine system. He recommended that I stick with the compressor and get that gun. It was a good recommendation. And, it was a lot less expensive than what I thought I wanted to buy.

Bob, thanks for this info. The reviews for the Qualspray AM-5008P are great, and Jeff's name is everywhere as well. I'm going to look seriously at that set-up!

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Ken Mitchell
Durham, NC

You may not think this regulator and the HF cheapie are air regulators, but they regulate the pressure at the gun just fine and can be set to hold the pressure unlike simple restricting valves. Try one you might like it.

Another Jeff Jewitt spray gun to consider: QS-125WB. Very nice package, and works fine with small compressors.

Another vote for the QualSpray guns. I sold an Iwatta and grabbed the AM-8008/5008 kit. The Iwatta was great, but the QualSprays work better with my small California Air Tools compressor (which is a dream come true compared to my old 1000 decibel compressor)

Between the two guns, I've used the larger of the two exclusively so far. I believe it's the 8008.