Air Compressor pressure drop...whats going on.

nismomans13 · Oct 20, 2010

So i'm trying to figure this out. I have a 60 gallon 2 stage compressor, 16cfm @90psi. If I open my regulator to 90psi and use say my die grinder, if I hold it in for about 3 seconds i'm down to 60psi of pressure at the regulator.

The regulator is 3/8 to 1/4in reducer, and the air hose is 1/2 in. Could my problem simply be I should use a smaller air line to match the output of my regulator. I'm thinking that the 1/4in to 1/2 in is creating a bottle neck and thats where my pressure drop is coming from.

KenC · Oct 20, 2010

What is your tank pressure that you are regulating? With some regulators, you have to set the pressure with the air moving.

MattT · Oct 20, 2010

If the regulators 1/4" output was causing a pressure drop you wouldn't see that at the gauge which is upstream of the restriction.

If the tank pressure isn't falling off the regulator is most likely your problem. Less likely is something between the tank and regulator.

z28snksknr · Oct 20, 2010

It sounds like you need a larger regulator. Yours is not allowing sufficient flow during use to maintain the downstream pressure.

In other words, your demand on the system is greater than the regulator can flow at that setpoint, so the pressure downstream of the regulator is lower. A regulator that has a higher flow capacity should be able to hold a tighter setpoint during use.

larry_g · Oct 20, 2010

nismomans13 said:
So i'm trying to figure this out. I have a 60 gallon 2 stage compressor, 16cfm @90psi. If I open my regulator to 90psi and use say my die grinder, if I hold it in for about 3 seconds i'm down to 60psi of pressure at the regulator.

The regulator is 3/8 to 1/4in reducer, and the air hose is 1/2 in. Could my problem simply be I should use a smaller air line to match the output of my regulator. I'm thinking that the 1/4in to 1/2 in is creating a bottle neck and thats where my pressure drop is coming from.

Your load is simply flowing more air than your system can deliver. I would suggest that you bypass the regulator and make sure that all fittings between the tank and the tool be as large as is practical. Then if you are above the max operating pressure of the tool then back off the switch to cut out at the max pressure. If you understand that pressure is caused by the restricting of flow then you'll understand that what you are seeing is not unusual.

lg
no neat sig line

nismomans13 · Oct 20, 2010

Tank pressure is 165psi and this is the regulator i'm using

My old craftsman 33 gallon had the same problem, but not NEARLY as bad, I would set it to 100psi to run a tool at 90, i'm setting this to almost 130psi to get 90psi at the tool. The regulator on my old compressor was a Husky. I don't see what could be restricting air pressure before the regulator, it comes out of the compressor, makes a 90 and its a straight 3/8id pipe to the regulator.

Larry, i'm not entirely sure what you mean. Do you mean make my air compressor tank pressure what I operate my tools at? If so that sorta defeats the purpose of the compressor i bought.

What are you guys using, regulator wise, and what kind of pressure drops are you seeing?

lametec · Oct 20, 2010

There's only a couple things that can cause this:

1. The regulator is starving for air (i.e., compressor doesn't supply enough).
2. The regulator is starving the tool (i.e., regulator doesn't flow enough).

With that said, the words "die grinder" and "1/4" reducer" should never be used in the same sentence unless there's a "bad idea" somewhere in there too. Die grinders use a lot of air. However, with that said as well, the 1/4" reducer is not your problem, as it sits after the regulator.

Why would you put a 1/4" reducer leading into a 1/2" hose, though? At least go directly from the 3/8" output of the regulator into the 1/2" hose.

larry_g · Oct 20, 2010

nismomans13 said:
Tank pressure is 165psi and this is the regulator i'm using

Larry, i'm not entirely sure what you mean. Do you mean make my air compressor tank pressure what I operate my tools at? If so that sorta defeats the purpose of the compressor i bought.

QUOTE]

I suggest that you try what I said as to prove that the regulator is what is restricting your flow. Pop the top off that regulator and look at the small hole all your air has to pass through. I run my system at ~110 psi and do not use a regulator unless needed.

What was your purpose of buying a 2 stage compressor?

lg
no neat sig line

jam0o0 · Oct 20, 2010

it's how you've set the regulator. you set regulators with the air moving through them. who cares what the reg says when you're not using the tool.

larry_g · Oct 20, 2010

jam0o0 said:
it's how you've set the regulator. you set regulators with the air moving through them. who cares what the reg says when you're not using the tool.

I care a lot what the static pressure is if there is a cylinder at the other end of the line that needs a controlled force. I also care if it a relieving or non-relieving regulator. If your regulator is big enough it will show minimal drop between static and dynamic.

lg
no neat sig line

MattT · Oct 20, 2010

nismomans13 said:
What are you guys using, regulator wise, and what kind of pressure drops are you seeing?

I'm running a SMC 3000 (3/8") series. Get maybe 5 psi drop between static and running my IR Thundergun which is my highest demand air tool. I've got a 5 micron filter before it so the reg might not be responsible for all of the drop.

Personally I'd go with a full size 3/8" regulator from one of the name brand pneumatics companies. Watch the max input pressure because a lot of them are only rated 150 psi.

ZRX61 · Oct 20, 2010

jam0o0 said:
it's how you've set the regulator. you set regulators with the air moving through them. who cares what the reg says when you're not using the tool.

What he said, I ALWAYS set regulators with load being applied.

Jeepguy · Oct 20, 2010

this might be a dumb question, but how old is that filter regulator unit? you might just need to replace the filter element in that unit. or just to see if it is the element take the bowl off remove the element, put it back together and see if it maintains pressure.

nismomans13 · Oct 20, 2010

The filter/regulator is brand new. I'm going into a 1/4in fitting because well all my air tools are 1/4in and thats all i had and its all i've used from day 1. I don't understand what my reasoning for buying a 2 stage compressor has to do with anything, but I bought it because of the cfm rating and price.

I did NOT set the regulator with air moving through it so I suppose that could be my problem. I also had a couple small leaks in the piping that i've fixed but haven't fired up the compressor to verify that yet. I'll give it a try tomorrow. But I really can't imaging this compressor doesn't move enough air for a simple blow gun, even the blow gun is causing a serious pressure drop at the regulator. I expect a certian amount of pressure drop but not setting it statically to 90psi and when i run a tool the pressure drops to 65-70 that seems pretty excessive even for my highest consumption air tools.

larry_g · Oct 21, 2010

nismomans13 said:
The filter/regulator is brand new. I'm going into a 1/4in fitting because well all my air tools are 1/4in and thats all i had and its all i've used from day 1. I don't understand what my reasoning for buying a 2 stage compressor has to do with anything, but I bought it because of the cfm rating and price..

The reasoning I wanted you to explain is why you bought a compressor capable of 175psi when you probably only need 120. There are plenty of single stage compressors avaiable that will give lots of CFM's. All that electrical energy that you are using to increase the pressure above necessary operating pressure is costly.

I did NOT set the regulator with air moving through it so I suppose that could be my problem. I also had a couple small leaks in the piping that i've fixed but haven't fired up the compressor to verify that yet. I'll give it a try tomorrow. But I really can't imaging this compressor doesn't move enough air for a simple blow gun, even the blow gun is causing a serious pressure drop at the regulator. I expect a certian amount of pressure drop but not setting it statically to 90psi and when i run a tool the pressure drops to 65-70 that seems pretty excessive even for my highest consumption air tools.

This dropping of pressure is simply the regulator not being able to do the job you ask of it.

lg
no neat sig line

MrMark · Oct 21, 2010

larry_g said:
The reasoning I wanted you to explain is why you bought a compressor capable of 175psi when you probably only need 120. There are plenty of single stage compressors avaiable that will give lots of CFM's. All that electrical energy that you are using to increase the pressure above necessary operating pressure is costly.

This dropping of pressure is simply the regulator not being able to do the job you ask of it.

lg
no neat sig line

Why is that? Is the pressure vs. energy consumption a nonlinear curve?

larry_g · Oct 21, 2010

MrMark said:
Why is that? Is the pressure vs. energy consumption a nonlinear curve?

Think about what the first thing the compressor does after the air is compressed. It goes to the cooler to remove the heat energy. Then it goes into the secondary cylinder(s). The more the air is compressed, the hotter it gets, the more heat energy that has to be removed. So to answer your question, yes.

lg
no neat sig line

lwlobo · Oct 21, 2010

Get a bigger regulator, should take care of it. Pressure difference between static and flow condition are always different, but it should be small. The difference goes down as the quality and size of the regulator go up.

Higher pressure gives you extra storage and flow capabity, but does hurt your effeciency.

nismomans13 · Oct 21, 2010

well i did as larry suggested. I ran my compressor tank pressure down to 100psi. However I did not bypass the regulator, I instead opened it up and allowed it to read 100psi, when I ran my die grinder the gauge on the regulator didn't move one bit.

Now does that mean the regulator is my problem? Since when the tank pressure is 165psi the regulator is dropping pressure 20-30psi while running a tool. Because there is a tank pressure gauge prior to the regulator and that gauge doesn't budge while running a tool which suggests the the pressure in the line is constant until it reaches the regulator.

Looks like a trip to grainger to pickup a 1/2 speedair regulator is in order here.

The other reason for a 2 stage compressor is the fact that it stores more air so to say, my other compressor would run ALL the time. I wouldn't even get one wheel off my truck and it kicked on.

nismomans13 · Oct 22, 2010

welp as everyone said the cheapo made in china craftsman regulator was the issue. I replaced it with a 1/2in speedaire unit today, opened it to 90psi ran my die grinder and the gauge didn't move 1 psi.

larry_g · Oct 22, 2010

Good to hear you got it sorted.

lg
no neat sig line

nismomans13 · Oct 23, 2010

well for anybody who needs to know in the future, I don't care how much CFM@90psi that cman unit was rated to, its not true because it coudln't even keep up with a blow gun at 90psi.

I cranked my speedaire up to 150psi and used my blow gun and it held strong at 150psi.

RalphL · Apr 20, 2012

Hi - this is an excellent post. I have a very similar setup as yours and experienced the EXACT same problem today in using a D/A sander (i.e., setting regulator to 100 psi and then sudden drop to 60 psi after running).

I am interested in the Speedaire.

nismomans13 - is the Speedaire model 4ZK91 similar to the one you purchased ---like this?
http://www.drillspot.com/products/35998/Speedaire_4ZK91_Air_Line_Filter_Regulator?s=1

Any help is appreciated.

Thanks!

Ralph

Air Compressor pressure drop...whats going on.

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