air pressure regulation

Thanks for your prompt response. No, I too thought at first that the regulator may have been faulty, so I replaced it, with a unit manufactured by "SMC" and it is a top line product. Its capacity is adequate in that it was recommended by the distributor, who deals in compressed air, paint spraying equipment. Norm

If I read your answer correctly you have replaced the original regulator with another new one and are having the same result? so it would appear the problem is prior to the regulator? You did not state if the pressure falling away was indicated by the low pressure gauge of the regulator and also by the high pressure gauge, if so then the supply line to your regulator is restricted or is an incorrect supply line. If the pressure gauges indicate correct pressure when using the spray gun then the fault is in your gun, it would be very unlikely to be a faulty hose [quickly tested by leaving the hose disconnected and checking the air flow]. If your gun has an air volume valve check it is allowing full air flow.

If you follow these checks it will isolate the faulty area

There is no fault. All compressor/gun combo's will result in a pressure drop when triggered, even an airbrush. You should always set your pressure at the gun, with the gun triggered. Fit a regulator/gauge the gun end of the hose, trigger the gun and adjust the pressure.

The paint sprayer should have an SCFM rating of air required at some pressure. The regulator should also have an SCFM rating at some ΔP; this needs to exceed the sprayer requirement. If the flow rate of the regulator is too low, or if anything is plugged in the lines or the regulator, your symptoms will follow. Some defect in the regulator might be responsible, but don't overlook these other questions.

Looks to me that your reducer has not enough capacity= too small or your air/water separator - if any - or filter is too small or clogged.

check also for pieces of teflon (tape) that may partially clog the line. Maybe not accurately applied. And 10 mm is maybe enough for a rodent or an elephant to crawl in the line.

One thing you have failed to mention is the length of your hose.... Here is a calculator, though its in US Units. http://www.gates.com/industrial/pressure/airflow.cfm?location_id=3043

I hope this helps you.

Have you checked the flow with any other tools? Perhaps the stone filter in the gun is partially plugged or there is some other obstruction.

You should install a small regulator on the gun it's self.

The pressure falls away? How do you messure that and where? I sprayed a lot with your settings. If your gun is suction operated (pot under the gun) your paint has to be light (very liquid) - with a pot on top you can go slightly less diluted. If your side- air (spray patern horizontal/vertical) is closed and the paint too thick you have no pressure out of your gun ( paint clogs it) With bigger guns this doesn't happen. What size nozzle you spry with?

Invariably the problem you are having is due to pressure drop caused by a restriction of flow, this may be due to a restriction in the size if any of the components between the air receiver and the spray gun, I have experienced this problem with customers installations on many occasions and in my experience, little consideration is given to compatibility of the components used, the filter/ regulator you are using may be too small for the task, it may be old and the filter may be in need of replacement, low cost filter/regulators may be fitted with a filter that is not cleanable or replaceable and a new replacement may be required to cure the problem.There is also a possibility that pressure drop could be caused by excessive hose length, the further you work from the air receiver the larger (diameter) the hose required for the compressed air to reach the point of use without pressure drop.

I hope this helps

I think when you increase the size of the tube you increasing usage of air. so please check capacity volume of air that compressor could deliver. I guess if compressor is under capcity .

Increasing the size of the tube has no effect on the consumption of air, consumption is dictated by the spray gun.

From a plumbing perspective, many regulators are symmetrical, which means they can be installed backwards. Make sure the arrow on the regulator points in the desired flow direction.

How big is the tank? reservoir etc

What is the output of the Compressor, and what type ? ie Piston. Diaphragm. Rotary vane etc?

I suspect from the information given, that either the compressor cannot cope or the reservoir/tank is to small.

ps just a thought, the compressor isn't one of those you use to blow up tyres is it?

I concur that the question of the compressor being up to the task is worth checking into. Even though a spray gun looks small and innocuous, it has an orifice at the end that is just an open hole to the atmosphere (about 1/8" diameter if I remember right). A pin hole on the end of a long system with many items depending on the system will drag down everything in the plant and cost you tens of thousands of dollars a year!

Generally, with a large air user like that, you need a large tank, LARGE hard piping from tank to usage point, and a large hose that is as short as practical. Leave the entire line pressure as high as possible (remembering that the higher the pressure, the more expensive leaks become) with your regulator at the gun.

Not knowing your set-up, I will take a couple of stabs:

1. If you are using a small roll-around compressor (single stage and cheap), it may simply not be up to the task. It will run constantly, and WILL lose pressure as you use it. Cheap fix: Buy as large of a tank as you can find/afford, and install it permanently where you are going to paint (or put it on casters if you move around). Put two quick disconnects directly at the tank and plug your small compressor into it first thing while setting up. It will take forever to pump up (remember HIGH pressure is your friend here), but it will give you a large reserve to paint from. Plug your gun into the other one with as short a large diameter hose as possible and the regulator at the gun. Go ahead and paint, and the large tank will give you the reserve you need to paint until it is time to rearrange parts. While rearranging your small compressor will have time to catch up. Painting is not a continual process all day long, but it does eat air at an alarming rate during the 5-10 minutes you will be using it hard. Proper fix: Step up to an industrial two-stage (or preferably screw) compressor with an industrial sized tank.

2. If you do actually have an industrial sized compressor, then increase the size of the piping to the paint area, and install an auxiliary tank at the paint booth. Use the one from step one above if you take this in steps due to cost. Do everything else the same.

3. If you are going to buy an industrial compressor - and you do this often for profit - step up to a small screw compressor. They run cheaper, run quieter, last 10x longer, and keep up better. Be sure to get one large enough to exceed the usage of the gun, and preferably twice as big (so you can grow in the future). This will be a $5000 to $7500 (as opposed to $600 for a cheap-o twin reciprocator on a vertical tank) cost of admission to the game, but you won't regret it after you give the receipt to your tax preparer for the Equipment deduction. 'Bamma will let you write off 100% and you will never have to buy another compressor. I still recommend installing the holding tank at the paint booth.

The name of the game is to get as much air as possible to the paint gun's inlet as quickly as possible, then reduce it for the control of the painting process. Greater pressure moves air faster. Anything you transfer the air through will slow it down, therefor the large auxiliary tank gives you a large volume of high pressure in reserve for you to dip into as need be while spraying and gives the compressor time to catch up later while you are getting ready for the next hard spray session.

If your compressor is running constantly, it is too small and will eventually burn out. Always remember that and whatever you use will treat you well for many years.

I think that you are overlooking the fact that when you have flow you will also have a pressure drop to some extent. Does the gauge drop slightly and then stabilize? The point that it drops to and stays is your actual operating pressure.

If it does then you only need to adjust it to compensate for the length of hose and other restrictions in your system and use it.

The gauge is taken off of a T type of fitting on the regulator and this causes something of a venturi, plus the flow of the air will also lower the pressure as well.

I think you have a normal system and just need to go with it and not a problem.

Rich Hurd

Fantastic, someone finally worked it out. Yes, you'll always get a pressure drop when you trigger any air powered tool, mainly due to friction inside the hose. Can't be helped. I usually have a small gauge attached to the spray gun inlet. This is where you set your spray pressure. Many years ago I was taught a formula for calculating the pressure drop over the length of hose. It involved the hose length, the internal dia. and the cfm rating of the gun (or other tool). Nothing else matters. When painting, I use an 8mm hose for the last 10 feet to the gun. For longer lengths (up to 15m) I use 10mm hose with a Teflon lining. The calcs are all approximate so invest in a small gauge and regulator, with the appropriate connectors and set your pressure there, with the gun triggered. While you're at it, get a small filter/water trap to put at the gun end too.

If I understood you fully that the cylinder remains at pressure, but only the line loses pressure in use. Then I get the impression that either the connector is simply too small "hole wise", or there is some debris in the tank, partially blocking the flow.....

I would switch it off, let all the pressure out, remove the fitting on the tank itself, then switch it on again. Do this ONLY with safety goggles on.

See what gets blown out.

If that does not sort it out then try all the fittings together on a known good compressor, one of them will cause the problem again there I am sure....

You are testing the gun without paint. When spraying paint the air in the gun pushes a lot of paint which causes the pressure to be maintained better than when the gun is dry fired. Test the gun spraying water before you do a lot of work to solve a problem you may not even have. best wishes, Mr. Gee

Pressure drops are caused by flow restrictions. Since you have tried larger hose and a new regulator, the one thing you have not mentioned is the couplings. These are notorious for restricting flow. Most of the auto painting I have done has been with no more than 25 psig at the gun. Most of the better spray guns have a regulator/gage at the gun for setting the pressure. Never rely on the regulator at the tank as you cannot get good regulation for the spray gun at the tank regulator. Since most newer spray guns are HVLP (High Volume Low Pressure) my guess is you just need a regulator/gage at the gun.

Absolutely! You need to get lots of air to the gun at low pressure. Do this by providing high pressure air to as near the gun as possible.

Restrictions will certainly slow down that flow, so follow all of the blockage trouble-shooting above (Jamesw and other posts).

The pressure at the regulator has nothing to do with the pressure at the gun, When you pull the trigger the pressure at the regulator will always fall off. The real question is what is the minimum pressure you need at the gun. You will have to raise the pressure at the regulator (allot more than you think) to get an adequete amount to the paint gun. A small pressure gauge at the gun will let you know what the real pressure is at the gun. I have to run mine at 90lbs at the regulator to get enough pressure. The length the air has to travel is the culpret.

Hi Guys, I have sorted my problem !! It proved to be rubbish in the pipe from the compressor to the regulator !! As a retired electrician, I was completely in the dark, and I must thank you all for your many ideas, and suggestions. We have a saying, "One is only as strong as his circle of Friends" I have learnt a lot from you guys so please accept my sincere thanks! I proceed now to my next crisis, the re-spraying of my Series 2A land Rover, but who knows, maybe this will proceed smoothly. Thank you friends, Norm.

so no elephant in the line?

Not now, but I must admit it was a huge one !!!!!

What I also did when spraying cars, was connecting a small tank between the compressor and the spray gun and from that tank I ran a hose to the gun, just long enough to run around the car. The outlet to your gun on top of the tank gets your air dryer too and the tank keeps your pressure more stable. I had a regulator just in front of the tank too. Pressure drops can show in the finish brilliance of your paint. Good luck.

Good news that you have found and fixed your problem.

Also thanks for letting us all know as well, that is very important to us!

I am "big-headed" enough to also write:-

Your description fitted the fault you eventually found correctly. That is basically what I said in my post (#20 ?) you should look for, eg.how to find debris in the situation you described so well.

It amazes me though just how many of our Brethren here did not read ALL the details you so correctly gave and went off in tangents to the main problem.....

That proves again that CR4 people are a lot of "speed readers" (noticed it before here and I am one myself, but I "slow down" for detailed infos) who do not take the time to stop and concentrate for a few moments!!!

None of you should be/get upset due to the critique, but in the future, DO please read more carefully......

Remember, the infos were there for us all in Normbourne's Posts.......we all started from the same point of reference.

Have a great day.

Hi Andy,

To state the bleeding obvious if you read my post 14 you will see I described the problem areas exactly.

Yes posts should be read more carefully. I find it a bit frustrating when people waffle on about all sorts of things without querying answer posts, giving one the feeling that as you say they do not read and think about these answers.

I was even mildly reprimanded that my analyses was faulty and not a GA in site.

Yes, Ca-Vin screwed up with his critique!!!!

I bet he's now very and probably a lot.......

What have I said or done Andy? I certainly did NOT criticise, just stated the facts as I was taught. Talk about "speed reading".

I await your apology.

You didn't critic me, it was someone else you offended......

But he complained/mentioned it to me....

He posted a very close fix in #14 if I remember correctly that you sort of jumped on as being wrong..... wrongly!!

Don't take it all too seriously though!! We all like having fun here!!

Have a great day in spite of us!!

OK guys, enough is enough, cant we let the matter rest? I valued everyones input and it is important that in any matter, every avenue is explored fully, and ideas are tossed around freely. Surely this is as it should be, and, in my opinion, is the way forward? One shouldn't be inhibited from making a suggestion, in the fear that one may be wrong! So lads, lets move on to our next "insoluble" problem. Thanks again guys, all the best, Norm

I agree.

GA.

First press the trigger and then adjust the air regulator till you get the right spray.

Once you get the hang of it you will know at which pressure you need to set the what to spary!

If you had bothered to read previous posts, you would have seen that the problem has been fixed for several days, a blockage in the airline......

Have a great day anyway.....

Sorry Andy. I should have.

My friend, you weren't the first to do that (I think it was me!!) and you certainly won't be the last either!!

Have a great day.